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Homocysteine‐lowering interventions for preventing cardiovascular events

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Abstract

Background

Cardiovascular disease, which includes coronary artery disease, stroke and peripheral vascular disease, is a leading cause of death worldwide. Homocysteine is an amino acid with biological functions in methionine metabolism. A postulated risk factor for cardiovascular disease is an elevated circulating total homocysteine level. The impact of homocysteine‐lowering interventions, given to patients in the form of vitamins B6, B9 or B12 supplements, on cardiovascular events has been investigated. This is an update of a review previously published in 2009, 2013, and 2015.

Objectives

To determine whether homocysteine‐lowering interventions, provided to patients with and without pre‐existing cardiovascular disease are effective in preventing cardiovascular events, as well as reducing all‐cause mortality, and to evaluate their safety.

Search methods

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2017, Issue 5), MEDLINE (1946 to 1 June 2017), Embase (1980 to 2017 week 22) and LILACS (1986 to 1 June 2017). We also searched Web of Science (1970 to 1 June 2017). We handsearched the reference lists of included papers. We also contacted researchers in the field. There was no language restriction in the search.

Selection criteria

We included randomised controlled trials assessing the effects of homocysteine‐lowering interventions for preventing cardiovascular events with a follow‐up period of one year or longer. We considered myocardial infarction and stroke as the primary outcomes. We excluded studies in patients with end‐stage renal disease.

Data collection and analysis

We performed study selection, 'Risk of bias' assessment and data extraction in duplicate. We estimated risk ratios (RR) for dichotomous outcomes. We calculated the number needed to treat for an additional beneficial outcome (NNTB). We measured statistical heterogeneity using the I2 statistic. We used a random‐effects model. We conducted trial sequential analyses, Bayes factor, and fragility indices where appropriate.

Main results

In this third update, we identified three new randomised controlled trials, for a total of 15 randomised controlled trials involving 71,422 participants. Nine trials (60%) had low risk of bias, length of follow‐up ranged from one to 7.3 years. Compared with placebo, there were no differences in effects of homocysteine‐lowering interventions on myocardial infarction (homocysteine‐lowering = 7.1% versus placebo = 6.0%; RR 1.02, 95% confidence interval (CI) 0.95 to 1.10, I2 = 0%, 12 trials; N = 46,699; Bayes factor 1.04, high‐quality evidence), death from any cause (homocysteine‐lowering = 11.7% versus placebo = 12.3%, RR 1.01, 95% CI 0.96 to 1.06, I2 = 0%, 11 trials, N = 44,817; Bayes factor = 1.05, high‐quality evidence), or serious adverse events (homocysteine‐lowering = 8.3% versus comparator = 8.5%, RR 1.07, 95% CI 1.00 to 1.14, I2 = 0%, eight trials, N = 35,788; high‐quality evidence). Compared with placebo, homocysteine‐lowering interventions were associated with reduced stroke outcome (homocysteine‐lowering = 4.3% versus comparator = 5.1%, RR 0.90, 95% CI 0.82 to 0.99, I2 = 8%, 10 trials, N = 44,224; high‐quality evidence). Compared with low doses, there were uncertain effects of high doses of homocysteine‐lowering interventions on stroke (high = 10.8% versus low = 11.2%, RR 0.90, 95% CI 0.66 to 1.22, I2 = 72%, two trials, N = 3929; very low‐quality evidence).

We found no evidence of publication bias.

Authors' conclusions

In this third update of the Cochrane review, there were no differences in effects of homocysteine‐lowering interventions in the form of supplements of vitamins B6, B9 or B12 given alone or in combination comparing with placebo on myocardial infarction, death from any cause or adverse events. In terms of stroke, this review found a small difference in effect favouring to homocysteine‐lowering interventions in the form of supplements of vitamins B6, B9 or B12 given alone or in combination comparing with placebo.

There were uncertain effects of enalapril plus folic acid compared with enalapril on stroke; approximately 143 (95% CI 85 to 428) people would need to be treated for 5.4 years to prevent 1 stroke, this evidence emerged from one mega‐trial.

Trial sequential analyses showed that additional trials are unlikely to increase the certainty about the findings of this issue regarding homocysteine‐lowering interventions versus placebo. There is a need for additional trials comparing homocysteine‐lowering interventions combined with antihypertensive medication versus antihypertensive medication, and homocysteine‐lowering interventions at high doses versus homocysteine‐lowering interventions at low doses. Potential trials should be large and co‐operative.

PICOs

Population
Intervention
Comparison
Outcome

The PICO model is widely used and taught in evidence-based health care as a strategy for formulating questions and search strategies and for characterizing clinical studies or meta-analyses. PICO stands for four different potential components of a clinical question: Patient, Population or Problem; Intervention; Comparison; Outcome.

See more on using PICO in the Cochrane Handbook.

Homocysteine‐lowering interventions (B‐complex vitamin therapy) for preventing cardiovascular events

Review question
We reviewed whether particular vitamins, which lower homocysteine, prevent cardiovascular events such as heart attack and stroke.

Background
Cardiovascular disease, which includes heart attacks and strokes, is the number one cause of death worldwide. Many people with cardiovascular disease may not have symptoms, but be at high risk. Diabetes mellitus, high blood pressure, smoking and a high cholesterol, as well as a family history of cardiovascular disease are well known risk factors. Elevated total homocysteine levels have recently been identified as a risk factor for cardiovascular disease. Homocysteine is an amino acid, its levels in the blood are influenced by blood levels of B vitamins: cyanocobalamin (B12), folic acid (B9) and pyridoxine (B6). This report is an update from a previous review published in 2015.

Study characteristics
The evidence is current to June 2017. We included 15 studies involving 71,422 participants living in countries with or without mandatory supplementation of foods with vitamins. These studies compared different regimens of B vitamins (cyanocobalamin (B12), folic acid (B9) and pyridoxine (B6)) with a control or any other comparison group. The studies were published between 2002 and 2015.

Key results
We found no evidence that homocysteine‐lowering interventions, in the form of supplements of vitamins B6, B9 or B12 given alone or in combination, at any dosage compared with placebo, or standard care, prevented heart attack or reduced death rates in participants at risk of, or living with cardiovascular disease. Homocysteine‐lowering interventions combined with antihypertensive medication had uncertain effects on stroke, approximately 143 people would need to be treated for 5.4 years to prevent 1 stroke. Homocysteine‐lowering interventions compared with placebo or any other comparison did not affect serious adverse events (cancer).

Quality of evidence
The quality of evidence from these studies was generally high.

Authors' conclusions

Implications for practice

In this third update of the review, there were no differences in effects of homocysteine‐lowering interventions in the form of supplements of vitamins B6, B9 or B12 given alone or in combination comparing with placebo on myocardial infarction, death from any cause or adverse events. In terms of stroke, this review found a small difference in effect favouring homocysteine‐lowering interventions in the form of supplements of vitamins B6, B9 or B12 given alone or in combination compared with placebo. There were uncertain effects of folic acid compared with enalapril plus folic acid on stroke; approximately 143 (95% CI 85 to 428) people would need to be treated for 5.4 years to prevent 1 stroke, this evidence emerged from one mega‐trial. Trial sequential analyses showed that additional trials are unlikely to increase the certainty about the findings of this issue regarding homocysteine‐lowering interventions versus placebo.

Implications for research

The association between both the lack of clinical effectiveness and harm of homocysteine‐lowering interventions might require further investigation into other homocysteine pathways. There is the need for additional trials comparing homocysteine‐lowering interventions combined with antihypertensive medication versus antihypertensive medication, and homocysteine‐lowering interventions at high doses versus homocysteine‐lowering interventions at low doses. Potential trials should be large and co‐operative.

Summary of findings

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Summary of findings 1. Homocysteine‐lowering interventions (Vitamin B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin) compared with placebo or standard care for preventing cardiovascular events

Homocysteine‐lowering interventions (vitamins B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin) compared with placebo or standard care for preventing cardiovascular events

Patient or population: adults at risk of or with established cardiovascular disease
Settings: outpatients
Intervention: homocysteine‐lowering interventions (vitamins B6 (pyridoxine; pyridoxal), B9 (folic acid) or B12 (cyanocobalamin).
Comparison: placebo or standard care

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants
(studies)

Quality of the evidence
(GRADE)

Comments

Assumed risk

Corresponding risk

Placebo or standard care

Homocysteine‐lowering interventions
(vitamins B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin)

Myocardial infarction
Follow‐up: 1 to 7.3 years

60 per 1000

61 per 1000
(57 to 66)

RR 1.02
(0.95 to 1.10)

46,699
(12 trials)

⊕⊕⊕⊕
high

Stroke
Follow‐up: 1 to 7.3 years

51 per 1000

46 per 1000
(42 to 50)

RR 0.90
(0.82 to 0.99)

44,224
(10 trials)

⊕⊕⊕⊕
high

Death by any cause
Follow‐up: 1 to 7.3 years

123 per 1000

124 per 1000
(118 to 130)

RR 1.01
(0.96 to 1.06)

44,817
(11 trials)

⊕⊕⊕⊕
high

Adverse events
Follow‐up: 3.4 to 7.3 years

85 per 1000

91 per 1000
(85 to 97)

RR 1.07
(1.00 to 1.14)

35,788
(8 trials)

⊕⊕⊕⊕
high

Cancer is the only reported adverse event.

*The basis for the assumed risk (e.g. the median control group risk across studies) is the outcomes of the study control arms. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

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Summary of findings 2. Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose) for preventing cardiovascular events

Homocysteine‐lowering interventions (high dose) compared with homocysteine lowering interventions (low dose) for preventing cardiovascular events

Patient or population: adults at risk of or with established cardiovascular disease
Settings: outpatients
Intervention: homocysteine‐lowering interventions (high dose) either (folic acid; vitamin B12 (cyanocobalamin) and vitamin B6 (pyridoxine; pyridoxal) or folic acid
Comparison: homocysteine‐lowering interventions (low dose) either (folic acid; vitamin B12; vitamin B6 per day) or folic acid

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants
(studies)

Quality of the evidence
(GRADE)

Comments

Assumed risk

Corresponding risk

Homocysteine‐lowering interventions (low‐dose)

Homocysteine‐lowering interventions (high‐dose)

Myocardial infarction
Follow‐up: 2 years

44 per 1000

40 per 1000
(29 to 54)

RR 0.90
(0.66 to 1.23)

3649
(1 trial)

⊕⊕⊕⊝
moderate1

VISP 2004:

  • High dose (2.5 mg folic acid; 0.4 mg vitamin B12 (cyanocobalamin) and 25 mg vitamin B6 (pyridoxine; pyridoxal)

  • Low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6 per day).

Stroke
Follow‐up: 2 to 5 years

112 per 1000

101 per 1000
(74 to 137)

RR 0.90
(0.66 to 1.22)

3929
(2 trials)

⊕⊝⊝⊝
very low1, 2, 3

1. Li 2015a was conducted including only Chinese elderly females.Trial used only folic acid as homocysteine‐lowering intervention.

  • High‐dose folic acid (0.8 mg/d)

  • Low‐dose folic acid (0.4 mg/d))

2. VISP 2004:

  • High dose (2.5 mg folic acid; 0.4 mg vitamin B12 (cyanocobalamin) and 25 mg vitamin B6 (pyridoxine; pyridoxal)

  • Low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6 per day).

Death by any cause
Follow‐up: 2 years

64 per 1000

55 per 1000
(42 to 71)

RR 0.86
(0.66 to 1.11)

3649
(1 trial)

⊕⊕⊕⊝
moderate1

VISP 2004:

  • High dose (2.5 mg folic acid; 0.4 mg vitamin B12 (cyanocobalamin) and 25 mg vitamin B6 (pyridoxine; pyridoxal)

  • Low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6 per day).

Cancer

Not estimable

Li 2015a and VISP 2004 reported no information on this outcome.

*The basis for the assumed risk (e.g. the median control group risk across studies) is the outcomes of the study control arms. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

1 Downgraded one level for imprecision due to low number of events
2 Dowgraded one level for risk of bias as one trial (Li 2015a) was rated as having unclear risk of selection, conduction and detection biases
3 Downgraded one level for heterogeneity (I‐squared: 72%).

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Summary of findings 3. Enalapril plus folic acid compared with enalapril for adults with hypertension

Enalapril plus folic acid compared with folic acid for adults with hypertension

Patient or population: adults with hypertension
Settings: Chinese outpatients
Intervention: enalapril (10 mg) plus folic acid (0.8 mg)
Comparison: enalapril (10 mg)

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants
(studies)

Quality of the evidence
(GRADE)

Comments

Assumed risk

Corresponding risk

Folic acid

Enalapril plus folic acid

Myocardial infarction
Follow‐up: median 4.5 years

2 per 1000

2 per 1000
(1 to 4)

RR 1.04
(0.60 to 1.82)

20,702
(1 trial)

⊕⊕⊕⊝
moderate1

Stroke
Follow‐up: median 4.5 years

34 per 1000

27 per 1000
(23 to 32)

RR 0.79
(0.68 to 0.93)

20,702
(1 trial)

⊕⊕⊕⊕
high

First unstable angina pectoris episode requiring hospitalisation

Not estimable

CSPPT 2015 did not assess this outcome.

Death from any cause
Follow‐up: median 4.5 years

31 per 1000

29 per 1000
(25 to 34)

RR 0.94
(0.81 to 1.10)

20,702
(1 trial)

⊕⊕⊕⊕
high

Serious adverse event (cancer)
Follow‐up: median 4.5 years

8 per 1000

8 per 1000
(6 to 11)

RR 0.96
(0.71 to 1.31)

20,243
(1 trial)

⊕⊕⊕⊝
moderate1

CSPPT 2015 included either neoplasms benign, malignant or unspecified

*The basis for the assumed risk (e.g. the median control group risk across studies) is the outcomes of the study control arms. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

1Downgraded one level for imprecision due to low number of events.

Background

Description of the condition

The burden of cardiovascular disease

Cardiovascular disease is the number one cause of death worldwide (Barquera 2015; Smith 2012). The term cardiovascular disease covers a wide array of disorders, including diseases of the cardiac muscle and of the vascular system supplying the heart, brain and other vital organs. The most common causes of cardiovascular disease‐related morbidity and mortality are ischaemic heart disease and stroke (Li 2016; Maredza 2015; Oliveira 2015; Prabhakaran 2016).

The burden of cardiovascular disease is significant and ischaemic heart disease is the single largest cause of death worldwide (Bansilal 2015; Kwan 2016). Global deaths from cardiovascular disease increased by 41% between 1990 and 2013 (Roth 2015a). It has been pointed out that cardiovascular diseases cause more than 4 million deaths/year in the 53 countries of the World Health Organization European Region and over 1.9 million deaths in the European Union (Bansilal 2015). It has been estimated that there will be 7.8 million premature cardiovascular deaths in 2025 (Roth 2015b).

Cardiovascular diseases account for about one‐half of non communicable diseases deaths (Benziger 2016). The majority of cardiovascular disease deaths occur in low‐ and middle‐income countries (Barquera 2015; Benziger 2016; Oliveira 2015; Prabhakaran 2016). The major risk factors for cardiovascular diseases include tobacco use, high blood pressure, high blood glucose, lipid abnormalities, high levels of body mass index and physical inactivity (Barquera 2015; Lackland 2015; Li 2016; Roth 2015b; Singh 2015; Tzoulaki 2016; Yeates 2015).

Homocysteine as a risk factor for cardiovascular disease

In 1962, it was hypothesised that increased levels of total homocysteine may cause vascular disease: the homocysteine theory of arteriosclerosis (McCully 2015a). The pathways through which total homocysteine levels may cause damage to endothelial cells and lead to atherosclerosis have been widely described (Ganguly 2015; McCully 2015bPushpakumar 2014). It has been pointed out that homocysteine reduces the bioavailability of the nitric oxide, a potent vasodilator (Lai 2015b). Another mechanism would be through an integration of the roles of homocysteine and folic acid in cardiovascular pathobiology, known as methoxistasis (Joseph 2013). The molecular and cellular effect of homocysteine metabolism imbalance yields oxidative stress which is cytotoxic (Skovierova 2016). The cellular status of homocysteine is not correlated with the homocysteine levels in plasma, which may explain the considerable differences that there are between epidemiological, intervention and basic research reports (Hannibal 2016).

Homocysteine is a non‐proteinogenic amino acid derived in methionine metabolism (Skovierova 2016). Several observational studies had shown that a raised blood homocysteine level was a risk factor for cardiovascular events (Casas 2005; Danesh 1998; Eikelboom 1999; Ford 2002; Guthikonda 2006; HSC 2002; Jacobsen 2005; Kardesoglu 2011; Refsum 1998; Splaver 2004; Stampfer 1992; Wald 2002; Wang 2005; Williams 2010; Wu 2013). The public significance of raised circulating blood homocysteine levels has been considered (Shelhub 2008). Currently, there is no evidence to support cardiovascular risk reduction by homocysteine‐lowering interventions (Cybulska 2015; Li 2015; Martí‐Carvajal 2009; Martí‐Carvajal 2013; Martí‐Carvajal 2015 (three previous versions of this review)). The American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Goff 2014) and The European Guidelines on cardiovascular disease prevention in clinical practice (Perk 2012) ratify that homocysteine is not a causal risk factor for cardiovascular disease.

Circulating total homocysteine levels are composed of protein (albumin)‐homocysteine mixed disulfide, sulfhydryl form and low molecular weight disulfides (Mudd 2000). The normal levels of total homocysteine are close to 10 µmol/L (Mudd 2000). Hyperhomocysteinaemia is defined as the presence of an abnormally elevated concentration of plasma or serum total homocysteine (Mudd 2000). However, there is some controversy about the definition of the degree of hyperhomocysteinaemia. Fasting total homocysteine level concentrations between 12 µmol/L and 30 µmol/L are termed mild or moderate, while intermediate hyperhomocysteinaemia includes levels between 31 µmol/L to 100 µmol/L, and severe hyperhomocysteinaemia reflects values above 100 µmol/L (Maron 2006; Maron 2009). In the general population, the prevalence of hyperhomocysteinaemia is between 5% and 10% (Refsum 1998). However, rates may be as high as 30% to 40% in the elderly population (Selhub 1993).

Description of the intervention

B‐complex vitamins, cyanocobalamin (B12) (Fedosov 2012; Herrmann 2012; Kräutler 2012), folic acid (B9) (Crider 2011; Molloy 2012; Ohrvik 2011; Yetley 2011), and pyridoxine (B6) (di Salvo 2011; di Salvo 2012; Friso 2012; Mukherjee 2011), given as a supplement.

How the intervention might work

The B‐complex vitamins are essential for homocysteine metabolism; they are involved in both the transformation and excretion pathways of homocysteine (McCully 2015a; McCully 2015b). Supplementation with B‐complex vitamins reduces total homocysteine levels (Clarke 2007; HLTC 2005). There is some ambiguity regarding the function of pyridoxine (vitamin B6). Vitamin B6 supplementation has been shown to lower total homocysteine levels after a methionine load, which occurs in experimental situations. However, at least two studies have shown the contrary (Gori 2007; Sofi 2008). It is, as a result, believed to be a weak determinant of circulating total homocysteine levels.

Why it is important to do this review

This is the third update of this Cochrane review and has been performed to identify and review the latest evidence.

Objectives

To determine whether homocysteine‐lowering interventions, provided to patients with and without pre‐existing cardiovascular disease:

  1. are effective in preventing cardiovascular events and/or all‐cause mortality;

  2. are safe;

  3. differ in efficacy or safety.

Methods

Criteria for considering studies for this review

Types of studies

Randomised controlled trials (RCTs) with a follow‐up period of one year or longer.

Types of participants

Adults (over 18 years) at risk of, or with established cardiovascular disease. We excluded studies in patients with end‐stage renal disease.

Types of interventions

The interventions considered were vitamins B6 (pyridoxine; pyridoxal), B9 (folic acid) or B12 (cyanocobalamin) given alone or in combination, at any dosage, and via any administration route.

We made comparisons with placebo, or with differing regimens of vitamins B6, B9 or B12. When the included population was at risk of cardiovascular disease, we considered combinations of homocysteine‐lowering interventions with standard treatment (such as antihypertensives and statins) versus standard treatment alone.

Types of outcome measures

Primary outcomes

  1. Non‐fatal or fatal myocardial infarction.

  2. Non‐fatal or fatal stroke (ischaemic or haemorrhagic stroke).

Secondary outcomes

  1. First unstable angina pectoris episode requiring hospitalisation.

  2. Hospitalisation for heart failure.

  3. Death from any cause.

  4. Serious or non‐serious adverse events.

We defined serious adverse events according to the International Conference on Harmonisation (ICH) Guidelines (ICH‐GCP 1997), as any event that leads to death, is life‐threatening, requires hospitalisation or prolongation of existing hospitalisation and/or results in persistent or significant disability. We considered all other adverse events non‐serious.

Search methods for identification of studies

Electronic searches

We reran the searches previously run in 2008 (Appendix 1), 2012 (Appendix 2), and 2014 (Appendix 3). Search strategies for 2017 are shown in Appendix 4.

We updated the searches of the Cochrane Central Register of Controlled Trials (CENTRAL 2017, Issue 5), MEDLINE OVID (1946 to 1 June 2017), Embase OVID (1980 to 2017 week 22) and Web of Science (Thomson Reuters, 1970 to 1 June 2017). The search of LILACS was last run on 1 June 2017. In a previous version (Martí‐Carvajal 2009), we searched Allied and Complementary Medicine ‐ AMED (accessed through Ovid) and the Cochrane Stroke Group Specialised Register.

We used the Cochrane sensitive‐maximising RCT filters to search MEDLINE and Embase (Lefebvre 2011).

We imposed no language restrictions.

Searching other resources

We also checked the reference lists of all trials identified.

We also searched the World Health Organization International Clinical Trials Platform search portal (http://apps.who.int./trialsearch) and ClinicalTrials.gov (https://clinicaltrials.gov/).

We also searched websites of U.S. Food and Drug Administration (www.fda.gov) and European Medicines Agency (www.ema.europa.eu) for unpublished information on homocysteine‐lowering interventions.

We contacted authors and researchers to obtain further details for published studies.

Data collection and analysis

We conducted data collection and analysis according to the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

Selection of studies

Two authors (AMC and IS) independently screened the results of the search strategy for potentially relevant trials and independently assessed them for inclusion based on the inclusion criteria.

Data extraction and management

Two review authors (AMC and IS) carried out data extraction using a pre‐designed data extraction form that included publication details, patient population, randomisation, allocation concealment, details of blinding measures, description of interventions and results. We resolved discrepancies through discussion. We involved a third review author (DL) to check the data entered into the Review Manager software. Two review authors (AMC and IS) assessed the included studies and entered the information into tables; see Characteristics of included studies.

Assessment of risk of bias in included studies

All review authors independently assessed the risk of bias of the trials according to the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

We assessed the following domains.

  1. Generation of the allocation sequence

  2. Allocation concealment

  3. Blinding (or masking)

  4. Incomplete outcome data

  5. Selective outcome reporting

  6. Other bias

See Appendix 5 for details of domains.

Measures of treatment effect

We pooled the risk ratios (RR) with 95% confidence interval (CI) for the following binary outcomes: non‐fatal or fatal myocardial infarction, non‐fatal or fatal stroke (ischaemic or haemorrhagic), first unstable angina pectoris episode requiring hospitalisation, hospitalisation for heart failure, death from any cause and serious or non‐serious adverse events as recommended by Higgins 2011. We calculated the number needed to treat for an additional beneficial outcome (NNTB) if the RR was significant (P value = < 0.05). NNTB is a measure of assessment of clinical useful of the consequences of treatment (Laupacis 1988). We estimated NNTB with GraphPad software.

Dealing with missing data

For all included trials, we noted the levels of attrition. We contacted the first author of the paper if data were missing. We extracted data on the number of participants by allocated treatment group, irrespective of compliance and whether or not the participant was later thought to be ineligible or otherwise excluded from treatment or follow‐up. If we were not able to do so, we recorded for each study whether the results pertained to an intention‐to‐treat analysis or to available‐case analysis.

Assessment of heterogeneity

We quantified statistical heterogeneity using the I2 statistic, which describes the percentage of total variation across studies that is due to heterogeneity rather than sampling error (Higgins 2003). We considered statistical heterogeneity to be present if the I2 value was greater than 50% (Higgins 2011). When significant heterogeneity was detected (I2 > 50%), we attempted to identify the possible causes.

Assessment of reporting biases

We assessed asymmetry in funnel plots for myocardial infarction, stroke and death from any cause, and devoted to detect potential publication bias and other causes of asymmetry (Sterne 2001). We used the contour‐enhanced funnel plot for differentiating asymmetry due to publication bias from that due to other factors (Peters 2008). We assessed likelihood of publication bias with Harbord and Peters tests (Sterne 2011a; Sterne 2011b). We used STATA statistical software V.14.0 (StataCorp LP) to perform conventional and contour funnel plots.

Data synthesis

We pooled the results from the trials using the Review Manager software (RevMan 2014). We summarised the findings using a random‐effects model.

Trial Sequential Analysis

Meta‐analysis of cumulative data may run the risk of random errors ('play of chance') due to sparse data and repetitive analyses of the same data (Brok 2008; Brok 2009; Thorlund 2010; Thorlund 2011; Wetterslev 2008; Wetterslev 2009; Wetterslev 2017). In order to assess the risks of random errors in our cumulative meta‐analyses, we conducted diversity‐adjusted trial sequential analyses based upon the proportion with the outcome in the control group, an a priori set relative risk reduction of 20%, an alpha of 5%, a beta of 20% and the diversity in the meta‐analysis (CTU 2011; Thorlund 2009; Thorlund 2011). We conducted sensitivity analysis of the trial sequential analysis to estimate the potential need for further trials.

Subgroup analysis and investigation of heterogeneity

We performed subgroup analysis according to the type of intervention, and by trials including participants without cardiovascular disease versus trials including participants with cardiovascular disease.

Sensitivity analysis

We conducted a sensitivity analysis comparing the results using all studies and using only those with a low risk of bias.

'Summary of findings' tables

We used The Grading of Recommendations Assessment, Development and Evaluation (GRADE) proposals to assess the quality of the body of evidence associated with the following outcomes: myocardial infarction, stroke, death from any cause and cancer (Guyatt 2011). One review author constructed summary of findings Table 1; summary of findings Table 2; summary of findings Table 3 using the GRADEpro software (GRADEpro 2008). We involved a second review author to check the data.

GRADE classifies the quality of a body of evidence based on the extent to which one can be confident that an estimate of effect or association reflects the outcome being assessed (Guyatt 2008; Guyatt 2013).

Fragility Index

We calculated the fragility index (FI) if the RR was significant (P value = < 0.05). FI is a measure to identify the number of events required to change statistically significant results to non‐significant results (Walsh 2014). The FI was only applied to RCTs where the allocation 1:1 and to binary data. We estimated the FI with the Fragility Index Calculator.

Bayes Factors

We estimated the threshold for clinical relevance using a Bayes factor (Jakobsen 2014). This is a likelihood ratio indicate the relative strength of evidence for two theories (Dienes 2014; Goodman 1999; Goodman 2005). A Bayes factor is a comparison of how well two hypotheses (the null hypothesis ‐H0‐ and the alternative hypothesis ‐H1‐) predict the data (Goodman 1999). A Bayes factor provides a continuous measure of evidence for H1 over H0. When a Bayes factor is 1, the evidence does not favour either model over the other. As a Bayes factor increase above 1 (towards infinity) the evidence favours H1 over H0. As a Bayes factor decreases below 1 (towards 0) the evidence favours H0 over H1 (Dienes 2008; Dienes 2014; Dienes 2017). We used Dienes' Calculator for estimating Bayes factors.

Results

Description of studies

The search in June 2017 identified 1464 records, which resulted in 1073 unique references after duplicates were removed. After examining the titles and abstracts we excluded 1036 references. We obtained full reprints of the remaining 37 references for more detailed examination, of which 22 reports were excluded. The remaining 15 references identified were for three new randomised clinical trials (B‐PROOF 2015; CSPPT 2015; Li 2015a), 11 of which related to one of the new trials (CSPPT 2015).

In total, this updated review includes 15 randomised clinical trials, published between 2002 and 2015, involving 71,422 participants (B‐PROOF 2015; BVAIT 2009; CHAOS 2002; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; Li 2015a; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). See Figure 1 for details.


Study flow diagram.

Study flow diagram.

These trials are described in the section Characteristics of included studies. The length of follow‐up ranged from one to 7.3 years. The trials varied in size, characteristics of participant populations, duration, drug dosage and experimental design.

Included studies

Thirteen trials were conducted in participants with known cardiovascular disease, such as coronary artery disease, myocardial infarction, stable angina, unstable angina, stroke or intermittent claudication (B‐PROOF 2015; BVAIT 2009; CHAOS 2002; FOLARDA 2004; GOES 2003; HOPE‐2 2006; Li 2015a; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008), one trial included participants without any history of cardiovascular disease (CSPPT 2015); a further trial explicitly included participants with a history of non‐disabling cerebral infarction (VISP 2004).

Fourteen trials included participants with at least one of the following known cardiovascular risk factors: diabetes mellitus, hypertension, elevated total cholesterol, current smoking, or low high‐density lipoprotein (HDL) cholesterol (B‐PROOF 2015; BVAIT 2009; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; Li 2015a; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). This aspect was unclear for CHAOS 2002. One trial (WAFACS 2008) included participants with three or more coronary risk factors. One trial explicitly excluded participants with previously known hyperhomocysteinaemia (total plasma homocysteine > 18 μmol/L) (FOLARDA 2004).

BVAIT 2009 included participants with hyperhomocysteinaemia without diabetes and cardiovascular disease. HOPE‐2 2006 included participants without a history of coronary heart disease (CHD). WAFACS 2008 only included female participants. Li 2015a included hypertensive females with hyperhomocysteinaemia.

Eleven trials included more than 1000 participants (B‐PROOF 2015; CSPPT 2015; CHAOS 2002; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Two trials only included elderly participants (B‐PROOF 2015; Li 2015a).

Ten trials were compared with placebo (B‐PROOF 2015; BVAIT 2009; CHAOS 2002; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008), and two with standard care (FOLARDA 2004; GOES 2003), while two trials were randomised controlled trials (Li 2015a; VISP 2004), which compared doses of homocysteine‐lowering interventions. One trial compared antihypertensive medication plus a homocysteine‐lowering intervention versus antihypertensive medication alone (CSPPT 2015).

The intervention assessed by most of the trials was a combination of vitamins B6, B9 and B12 (B‐PROOF 2015; BVAIT 2009; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Five trials only included vitamin B9 as intervention (CSPPT 2015; CHAOS 2002; FOLARDA 2004; GOES 2003; Li 2015a). SU.FOL.OM3 2010 used 5‐methyltetrahydrofolate instead of folic acid.

FOLARDA 2004, GOES 2003, HOPE‐2 2006, NORVIT 2006, SEARCH 2010, WAFACS 2008 and WENBIT 2008 described lipid‐lowering drugs used as concomitant medications. SU.FOL.OM3 2010 reported omega 3 polyunsaturated fatty acids used as concomitant medications. B‐PROOF 2015 reported vitamin D3 use as a concomitant medication. Li 2015a reported restriction of salt intake and administration of vitamin B12 as a concomitant medication. CSPPT 2015 described the use of antihypertensive medications, angiotensin‐converting enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers, diuretics, β‐Blockers, lipid‐lowering medications, glucose‐lowering medications and antiplatelet medications concomitantly.

Three trials were conducted in a "fortified" population (BVAIT 2009; VISP 2004; WAFACS 2008). The programme was described as a "...nutritional intervention programme with a specifically defined target, and fortified food products are expected to become a main source of the specific added nutrient" (Wirakartakusumah 1998). Two trials were performed in a mixed population (HOPE‐2 2006; VITATOPS 2010), and 10 were carried out in non‐fortified populations (B‐PROOF 2015; CSPPT 2015; CHAOS 2002; FOLARDA 2004; GOES 2003; Li 2015a; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; WENBIT 2008).

Twelve trials used composite outcomes in their analyses (B‐PROOF 2015; CSPPT 2015; CHAOS 2002; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Four trials included revascularisation or other vascular procedures (CHAOS 2002; GOES 2003; WAFACS 2008; WENBIT 2008). Fourteen trials had stroke as the endpoint (B‐PROOF 2015; BVAIT 2009; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; Li 2015a; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Fourteen trials assessed the impact of the intervention on myocardial infarction rates (B‐PROOF 2015; BVAIT 2009; CHAOS 2002; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). One trial included angina pectoris as a component of composite outcomes (B‐PROOF 2015).

Thirteen studies reported the sample size calculation (B‐PROOF 2015; BVAIT 2009; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). The trials used 80% or 90% power to detect between a 20% and 50% reduction in endpoints.

Concentrations of total homocysteine blood levels at baseline were reported in 13 trials (B‐PROOF 2015; BVAIT 2009; CSPPT 2015; CHAOS 2002; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008WENBIT 2008). Six trials reported the total homocysteine blood levels at the end of follow‐up (B‐PROOF 2015; CHAOS 2002; HOPE‐2 2006; NORVIT 2006; VISP 2004; WAFACS 2008). WENBIT 2008 described total homocysteine blood levels after one year of the intervention. CHAOS 2002 did not report total homocysteine blood levels at baseline or at the end of follow‐up in the control arm. GOES 2003 reported total homocysteine blood levels at baseline and at the end follow‐up, but only for the intervention arm and not for the control arm. FOLARDA 2004 and Li 2015a did not report the circulating total homocysteine blood levels in either group.

Definitions used for defining myocardial infarction, stroke, unstable angina and death (all‐cause) are described in Appendix 6.

Excluded studies

This review has 66 references excluded (44 in the prior versions and 22 in this update), which are described in the table of Characteristics of excluded studies. These studies were mainly systematic reviews, RCTs with a follow‐up of less of one year, and non‐RCTs.

Risk of bias in included studies

The risk of bias in the included trials is summarised in Figure 2 and Figure 3, and detailed in the Characteristics of included studies tables. See Appendix 5 for details.


Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.


Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Allocation

Random sequence generation

The risk of bias arising from the method of generation of the allocation sequence was low in 10 trials (B‐PROOF 2015; BVAIT 2009; CSPPT 2015; GOES 2003; HOPE‐2 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008). Five trials had an unclear risk for this domain (CHAOS 2002; FOLARDA 2004; Li 2015a; NORVIT 2006; WENBIT 2008).

Allocation concealment

We rated the risk of bias arising from the method of allocation concealment as low in 10 trials (B‐PROOF 2015; BVAIT 2009; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Five trials showed an unclear risk for this domain (CHAOS 2002; CSPPT 2015; FOLARDA 2004; GOES 2003; Li 2015a).

Blinding

We rated the risk of bias arising from lack of blinding of participants and personnel as low in 11 trials (B‐PROOF 2015; BVAIT 2009; CSPPT 2015; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). The risk of bias from blinding was unclear in two trials (CHAOS 2002; Li 2015a). We rated the risk of bias arising from lack of blinding as high in two trials (FOLARDA 2004; GOES 2003).

Blinding of outcome assessment (detection bias)

We rated the risk of bias arising from lack of blinding of outcome assessment as low in 12 trials (BVAIT 2009; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). The risk of bias from unblinding was unclear in three trials (B‐PROOF 2015; CHAOS 2002; Li 2015a).

Incomplete outcome data

We rated the risk of attrition bias as low in eight trials (BVAIT 2009; CSPPT 2015; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010). We rated the risk of attrition bias as high in three trials (B‐PROOF 2015; FOLARDA 2004; WENBIT 2008). We rated the risk of bias as unclear in four trials (CHAOS 2002; Li 2015a; VISP 2004; WAFACS 2008).

Selective reporting

Fourteen trials had a low risk of bias in this domain. One trial was rated as having high risk of bias for selective reporting (Li 2015a) due to lack of information on adverse events.

Other potential sources of bias

Ten trials had a low risk of bias due to other sources of bias not identified (B‐PROOF 2015; BVAIT 2009; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Four trials had an unclear risk of bias (CHAOS 2002; FOLARDA 2004; GOES 2003; Li 2015a). One trial was rated as having high risk of bias (CSPPT 2015).

Overall risk of bias

Nine trials were rated as having low risk of bias (BVAIT 2009; CSPPT 2015; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008).

Effects of interventions

See: Summary of findings 1 Homocysteine‐lowering interventions (Vitamin B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin) compared with placebo or standard care for preventing cardiovascular events; Summary of findings 2 Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose) for preventing cardiovascular events; Summary of findings 3 Enalapril plus folic acid compared with enalapril for adults with hypertension

The results are based on 71,422 participants in 15 randomised clinical trials (B‐PROOF 2015; BVAIT 2009; CHAOS 2002; CSPPT 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; Li 2015a; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VISP 2004; VITATOPS 2010; WAFACS 2008; WENBIT 2008).

See summary of findings Table 1; summary of findings Table 2 and summary of findings Table 3 for details.

Primary outcomes

Non‐fatal or fatal myocardial infarction
Homocysteine‐lowering interventions compared with placebo or conventional care

A meta‐analysis of 12 randomised clinical trials (46,699 participants) showed uncertainty in the effect on non‐fatal or fatal myocardial infarction between homocysteine‐lowering interventions and placebo or conventional care (1788/25,051 (7.14%) versus 1290/21,648 (5.96%); risk ratio (RR) 1.02, 95% confidence interval (CI) 0.95 to 1.10; P value = 0.56, I2 = 0%; high‐quality evidence) (B‐PROOF 2015; BVAIT 2009; CHAOS 2002; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008) (Analysis 1.1). The Bayes factor was 1.04, which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other. Trial sequential analysis for myocardial infarction suggested that no more trials are needed to disprove a 10% relative risk reduction with the intervention. Smaller risk reductions might still require further trials (Figure 4). There was a low risk of publication bias (P value = 0.88, Harbord test; P value = 0.86, Peters test). Figure 5 and Figure 6 show funnel and contour‐enhanced funnel plots, respectively.


Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on myocardial infarction. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5.95% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on myocardial infarction. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5.95% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.


Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.


Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

Subgroup trials with a low risk of bias

A meta‐analysis of six trials (37,442 participants) found uncertainty over the effect of intervention in non‐fatal or fatal myocardial infarction rates (1517/19,649 (7.72%) versus 1161/17,793 (6.53%); RR 1.01, 95% CI 0.94 to 1.09, P value = 0.79, I2 = 0%) (HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008). (Analysis 2.1).

Subgroup analysis comparing trials including participants without or with history of cardiovascular disease

One trial (490 participants) including participants without cardiovascular disease found uncertainty between intervention and placebo groups regarding non‐fatal or fatal myocardial infarction (2/248 (0.81%) versus 2/242 (0.83%); RR 0.98, 95% 0.14 to 6.87, P value = 0.98) (BVAIT 2009). A meta‐analysis of 11 trials (46,209 participants) including participants with a history of cardiovascular disease showed that there was no difference in non‐fatal or fatal myocardial infarction between intervention and placebo groups (1786/24,803 (7.20%) versus 1288/21,406 (6.02%); RR 1.02, 95% CI 0.95 to 1.10, I2 = 9%) (B‐PROOF 2015; FOLARDA 2004; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Testing for subgroup differences found no significant difference (P value = 0.96 and I2 = 0%). Analysis 3.1.

Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose)

One trial (3649 participants) found a lower proportion had non‐fatal or fatal myocardial infarctions in participants assigned to a high dose of homocysteine‐lowering interventions compared with those receiving a low dose of homocysteine‐lowering interventions (72/1814 (3.97%) versus 81/1835 (4.41%); RR 0.90, 95% CI 0.66 to 1.23, P value = 0.50; moderate‐quality evidence) (VISP 2004) (Analysis 1.1). The Bayes factor was 1.06, which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other.

Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

One trial (20,702 participants) found uncertainty in the rates of non‐fatal or fatal myocardial infarction between intervention and control groups (25/10,348) (0.24%) versus 24/10,354 (0.23%); RR 1.04, 95% CI 0.60 to 1.82, P value = 0.88; moderate‐quality evidence) (Analysis 1.1). The Bayes factor was 0.97 which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other.

Subgroup analysis for missing data

One trial (20,635 participants) comparing the combination of folic acid plus enalapril with enalapril alone showed inconsistent results in terms of non‐fatal or fatal myocardial infarction, according to per protocol analysis (25/10,316 (0.24%) versus 24/10,319 (0.23%); RR 1.04, 95% CI 0.60 to 1.82, P value = 0.89), best‐worst case scenario (25/10,348 (0.24%) versus 59/10,354 (0.57%); RR 0.42, 95% CI 0.27 to 0.68, P value = 0.0003) and worst‐best case scenario (57/10,348 (0.55%) versus 24/10,354 (0.23%); RR 2.38, 95% CI 1.48 to 3.83, P value = 0.0004). Testing for subgroup differences found a significant difference (P value <0.0001 and I2 = 92%) (CSPPT 2015). Analysis 4.1.

Non‐fatal or fatal stroke
Homocysteine‐lowering interventions compared with placebo

A meta‐analysis of ten trials (44,224 participants) showed a risk reduction in non‐fatal or fatal stroke in participants assigned to homocysteine‐lowering interventions compared with placebo (1014/23,809 (4.26%) versus 1034/20,415 (5.06%); RR 0.90, 95% CI 0.82 to 0.99, P value = 0.03, I2 = 8%, high‐quality evidence) (B‐PROOF 2015; BVAIT 2009; FOLARDA 2004; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008) (Analysis 1.2). The Bayes factor was 5.84 which means that it is 5.84 times more likely that homocysteine‐lowering interventions reduce non‐fatal or fatal stroke compared with placebo. Trial sequential analysis for stroke suggested that no more trials are needed to disprove a 10% relative risk reduction with intervention. Smaller risk reductions might still require further trials (Figure 7). There was a low risk of publication bias (P value = 0.368, Harbord test; P value = 0.393, Peters test). Figure 8 and Figure 9 show funnel and contour‐enhanced funnel plots, respectively.


Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on stroke. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5% with an alpha of 5% and beta of 20%.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on stroke. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5% with an alpha of 5% and beta of 20%.


Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.


Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Subgroup trials with a low risk of bias

A meta‐analysis of six trials (37,442 participants) found uncertainty in differences between non‐fatal or fatal stroke rates between intervention and placebo groups (919/19,649 (4.68%) versus 953/17,793 (5.36%); RR 0.90, 95% CI 0.80 to 1.02, P value = 0.10, I2 = 32%) (HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008). (Analysis 2.2).

Subgroup analysis comparing trials including participants without or with history of cardiovascular disease

One trial (490 participants) including participants without cardiovascular disease found uncertainty between intervention and placebo groups regarding the rates of non‐fatal or fatal stroke (0/248 (0%) versus 2/242 (0.83%); RR 0.20, 95% 0.01 to 4.04, P value = 0.29) (BVAIT 2009). A meta‐analysis of nine trials (43,734 participants) including participants with history of cardiovascular disease showed evidence of effect favouring intervention group versus placebo group in terms of non‐fatal or fatal stroke rates (1014/23,561 (4.30%) versus 1032/20,173 (5.12%); RR 0.90, 95% CI 0.82 to 0.99, I2 = 9%) (B‐PROOF 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Testing for subgroup differences found no significant difference (P 0.32 and I2 = 0%). Analysis 3.2.

Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose)

A meta‐analysis of two trials (3929 participants) showed uncertainty between the effects of high dose versus low dose of homocysteine‐lowering interventions with regards to non‐fatal or fatal stroke (211/1958 (10.78%) versus 221/1971 (11.21%); RR 0.90, 95% CI 0.66 to 1.22; I2 = 72%; very low‐quality evidence) (Li 2015a; VISP 2004) (Analysis 1.2). The Bayes factor was 1.06, which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other.

We detected high statistical heterogeneity, as conveyed by the I2 value (72%), and therefore we further explored by type of planned intervention.

One trial (3649 participants) comparing a combination of homocysteine‐lowering interventions (folic acid, vitamin B6 and vitamin B12), either at high dose (2.5 mg folic acid; 0.4 mg vitamin B12; 25 mg vitamin B6), or low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6) found uncertainty over the effects on non‐fatal or fatal stroke rates (152/1814 (8.38%) versus 148/1835 (8.07%); RR 1.04, 95% CI 0.84 to 1.29; P value = 0.73) (VISP 2004). Analysis 5.1

One trial (280 participants) conducted only with elderly female participants, compared folic acid at high dose (0.8 mg) plus vitamin B12 (500 μg) versus folic acid at low dose (0.4 mg) plus vitamin B12 (500 μg). It found a lower proportion of non‐fatal or fatal strokes in participants assigned to high‐dose folic acid than those receiving a low‐dose folic acid (59/144 (40.97%) versus 73/136 (53.68%); RR 0.76, 95% CI 0.59 to 0.98; P value = 0.03) (Li 2015a). Analysis 5.1

Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

One trial (20,702 participants) found a reduced risk of non‐fatal or fatal stroke in participants receiving enalapril plus folic acid compared with participants receiving enalapril as monotherapy (281/10348 (2.72%) versus 354/10354 (3.42%); RR 0.79, 95% CI 0.68 to 0.93, P value = 0.003; NNTB 143, 95% CI 85 to 428, high‐quality evidence) (Analysis 1.2). The Bayes factor was 31.9 which means that it is 31.9 times more likely that homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) alone reduces non‐fatal or fatal stroke. The fragility Index was 23.

Subgroup analysis for missing data

The overall incidence of non‐fatal or fatal stroke seemed to be reduced in people assigned to a combination of folic acid plus enalapril versus those allocated to enalapril alone: per protocol analysis (281/10,316 (2.72%) versus 354/10,319 (3.43%); RR 0.79, 95% CI 0.68 to 0.93; P value = 0.003), best‐worst case scenario (281/10,348 (2.72%) versus 389/10,354 (3.76%); RR 0.72, 95% CI 0.62 to 0.84; P value = 0.0001) and worst‐best case scenario (313/10,348 (3.02%) versus 354/10,354 (3.42%); RR 0.88, 95% CI 0.76 to 1.03; P value = 0.11). Test for subgroup differences: P = 0.18, I² = 42.5%. (CSPPT 2015). Analysis 4.2.

Secondary outcomes

First unstable angina pectoris episode requiring hospitalisation

Homocysteine‐lowering interventions compared with placebo

A meta‐analysis of four trials (12,644 participants) showed uncertainty between the effects intervention compared with placebo on the rate of unstable angina requiring hospitalisation (910/8015 (11.35%) versus 468/4629 (10.11%); RR 0.98, 95% CI 0.80 to 1.21, P value = 0.87, I2 = 66%) (FOLARDA 2004; HOPE‐2 2006; NORVIT 2006; WENBIT 2008) (Analysis 1.3.

Hospitalisation for heart failure

One trial found an uncertain effect in the hospitalisation for heart failure rates between intervention and placebo groups (202/2758 (7.32%) versus 174/2764 (6.30%); RR 1.16, 95% CI 0.96 to 1.41, P value = 0.13) (HOPE‐2 2006).

Death from any cause
Homocysteine‐lowering interventions compared with placebo

A meta‐analysis of 11 trials (44,817 participants) found uncertainty between the effects of intervention versus placebo on the rates of death from any cause (2821/24,109 (11.70%) versus 2544/20,708 (12.29%); RR 1.01, 95% CI 0.96 to 1.06, P value = 0.68, I2 = 0%, high‐quality evidence) (B‐PROOF 2015; BVAIT 2009; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008) (Analysis 1.4). The Bayes factor was 1.05, which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other. Trial sequential analysis for stroke suggested that no more trials are needed to disprove a 10% relative risk reduction with intervention. Smaller risk reductions might still require further trials (Figure 10). There was a low risk of publication bias (P value = 0.95, Harbord test; P value = 0.82, Peters test). Figure 11 and Figure 12 show funnel and contour‐enhanced funnel plots, respectively.


Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on death from any cause. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 12% from proportion event in control (Pc) group of 11.7% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on death from any cause. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 12% from proportion event in control (Pc) group of 11.7% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.


Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.


Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Subgroup trials with a low risk of bias

A meta‐analysis of seven trials (37,932 participants) found uncertainty between the effects of intervention versus placebo in rates of death from any cause (2145/19,897 (10.78%) versus 1923/18,035 (10.66%); RR 1.03, 95% CI 0.95 to 1.12; P value = 0.48; I2 = 41%) (BVAIT 2009; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008). (Analysis 2.3).

Subgroup analysis comparing trials including participants without or with history of cardiovascular disease

One trial (490 participants) including participants without cardiovascular disease found uncertainty between the effects of intervention versus placebo in rates of death from any cause (0/248 (0%) versus 2/242 (0.83%); RR 0.20, 95% 0.01 to 4.04, P value = 0.29) (BVAIT 2009). A meta‐analysis of 10 trials (44,327 participants) including participants with history of cardiovascular disease showed conclusive evidence that there was no difference in rates of death from any cause between intervention and placebo groups (2821/23,861 (11.82%) versus 2542/20,466 (12.42%); RR 1.01, 95% CI 0.96 to 1.06, I2 = 0%) (B‐PROOF 2015; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008). Testing for subgroup differences found no significant difference (P 0.32 and I2 = 0%). Analysis 3.3.

Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose)

One trial (3649 participants) found uncertainty in mortality from any cause between intervention and control groups (99/1814 (5.46%) versus 117/1835 (6.38%); RR 0.86; 95% CI 0.66 to 1.11; P value = 0.24; moderate‐quality evidence) (VISP 2004) (Analysis 1.4). The Bayes factor was 1.07 which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other.

Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

One trial (20,702 participants) found uncertainty between the effects of enalapril plus folic acid compared with participants receiving enalapril as monotherapy on mortality from any cause (302/10,348 (2.92%) versus 320/10,354 (3.09%); RR 0.94, 95% CI 0.81 to 1.10; P value = 0.47; high‐quality evidence) (Analysis 1.4). The Bayes factor was 1.08 which means that evidence is insensitive, the data are equally well predicted by both models and the evidence does not favour either model over the other.

The combination of folic acid and enalapril seemed not to affect the incidence of death from any cause compared with enalapril alone. Per protocol analysis (302/10,316 (2.93%) versus 320/10,319 (3.10%); RR 0.94, 95% CI 0.81 to 1.10; P value = 0.47), best‐worst case scenario (302/10,348 (2.92%) versus 355/10,354 (3.43%); RR 0.85, 95% CI 0.73 to 0.99; P value = 0.04) and (334/10,348 (3.23%) versus 320/10,354 (3.09%); RR 1.04, 95% CI 0.90 to 1.21; P value = 0.57). Test for subgroup differences: P = 0.17, I² = 43.3%. (CSPPT 2015). Analysis 4.3.

Serious or non‐serious adverse events

Homocysteine‐lowering interventions compared with placebo

A meta‐analysis of eight trials (35,788 participants) assessing cancer incidence found uncertainty in the incidence of cancer in intervention and placebo groups (1621/19,591 (8.27%) versus 1376/16,197 (8.50%); RR 1.07, 95% CI 1.00 to 1.14, P value = 0.07, I2 = 0%, high‐quality evidence) (B‐PROOF 2015; BVAIT 2009; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; WAFACS 2008; WENBIT 2008) (Analysis 1.5). Trial sequential analysis for adverse events suggested that no more trials are needed to disprove a 10% relative risk reduction (Figure 13).


Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on adverse events (cancer). The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 8.49% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on adverse events (cancer). The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 8.49% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

A meta‐analysis of three trials (13,802 participants) found uncertainty in terms of serious or non‐serious adverse events rather than cancer between intervention and placebo groups (322/6903 (4.66%) versus 312/6899 (4.52%); RR 1.02, 95% 0.88 to 1.19; P value = 0.77, I2 = 0%, high‐quality evidence) (BVAIT 2009; SEARCH 2010; SU.FOL.OM3 2010). Analysis 1.6.

Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

One trial (20,243 participants) found uncertainty in terms of cancer incidence between participants receiving enalapril plus folic acid compared with participants receiving enalapril as monotherapy (79/10,119 (0.78%) versus 82/10,124 (0.81%); RR 0.96, 95% CI 0.71 to 1.31; P value = 0.81; moderate‐quality evidence) (Analysis 1.5).

Discussion

Summary of main results

This updated Cochrane review of homocysteine‐lowering interventions (B vitamins) for preventing cardiovascular events identified 15 randomised controlled trials incorporating 71,422 participants. Trials reported different combinations of homocysteine‐lowering interventions compared with different control interventions (placebo: B‐PROOF 2015; BVAIT 2009; CHAOS 2002; FOLARDA 2004; GOES 2003; HOPE‐2 2006; NORVIT 2006; SEARCH 2010; SU.FOL.OM3 2010; VITATOPS 2010; WAFACS 2008; WENBIT 2008, homocysteine‐lowering interventions at low dose: Li 2015a; VISP 2004, and antihypertensive medication (enalapril): (CSPPT 2015)). Overall, the trials had a low risk of bias and were adequately powered. Participants differed somewhat in cardiovascular risk levels (some with established cardiovascular disease (CVD), others at high risk of CVD), baseline total homocysteine blood levels, access to foods fortified with folic acid or not, different dosages of vitamins and different control groups, with treatment periods varying from two to seven years.

1. This review found no reduction of the incidence of either myocardial infarction (fatal or non‐fatal) and death from any cause or an increasing risk of adverse events (cancer).

2. With regard to stroke (fatal or non‐fatal), a meta‐analysis of homocysteine‐lowering interventions compared with placebo, and one mega‐trial comparing folic acid plus enalapril with enalapril alone found a reduction of risk stroke in those treated. A meta‐analysis of two trials comparing high dose versus low dose of homocysteine‐lowering interventions did not find a difference in the rates of fatal or non‐fatal strokes.

Overall completeness and applicability of evidence

This updated review found evidence suggesting that homocysteine‐lowering interventions (vitamins B6, B12 and folic acid (B9)) are not useful for preventing myocardial infarction (fatal or non‐fatal) or death from any cause. We conducted a sensitivity analysis restricted to trials with low risk of bias for myocardial infarction and death from any cause. These results show consistency and are based on data from trials that included a broad range of participants with different co‐morbidities who received different treatment approaches. Although these aspects could be considered as a threat to applicability, the consistency in the results derived from our analyses showed that the included trials may represent a broad picture of participants with a high risk of cardiovascular events.

With reference to stroke (non‐fatal or fatal stroke), this update found that homocysteine‐lowering interventions reduce the incidence of stroke compared with placebo or enalapril alone (Analysis 1.2). However, this result should be viewed with caution. In the trial sequential analysis graph called 'Trial sequential analysis on stroke in 10 trials investigating homocysteine‐lowering interventions versus placebo' (Figure 7), it was observed that after 44,224 participants the Z curve crossed the upper conventional alpha of 5%, but also the cumulative Z‐curve crossed no the trial sequential alpha‐spending monitoring boundaries also called as monitoring efficacy boundary (Roshanov 2017). This positive result appears to be weak, due to the 95% confidence interval reduction of risk of any stroke ranging between 1% and 18% and the very low basal risk. As is shown into summary of findings Table 1, in the control group 51 people out of 1000 had a stroke (non‐fatal or fatal) over 1 to 7.3 years, compared with 46 (95% CI 42 to 50) out of 1000 for the active treatment group.

CSPPT 2015 also found a positive result of enalapril plus folic acid compared with enalapril on incidence of any stroke. The trial had a duration of follow‐up of five years. The absolute risk reduction in this trial was very low (0.7%), which explains the high number needed to treat for an additional beneficial outcome in this trial of 143 (95% CI 85 to 428). During five years between 85 and 428 hypertensive participants would need to take enalapril plus folic acid for to prevent one stroke. According to the summary of findings Table 3, in the control group 34 people out of 1000 had a stroke (non‐fatal or fatal) over five years, compared to 27 (95% CI 23 to 32) out of 1000 in the active treatment group. Therefore, the clinical difference is small between the groups, which is reflected in the sensitivity analysis shown into Analysis 4.2. We estimated the fragility index of CSPPT 2015 as 23, which denotes that if 23 patients in the experimental group were converted from not having the primary endpoint to having the primary endpoint, the study would lose statistical significance (P > 0.05). Furthermore, it is unknown whether such treatment would benefit a non‐Chinese population. In both cases (meta‐analysis with more than 40,000 and a trial with 20,000 participants) shows a highly significant statistical result, but it "may not represent a clinically important effect when treating patients in our daily lives." (Fuster 2015).

In conclusion, this updated version showed the same findings as the previous version (Martí‐Carvajal 2015). It showed that supplementary vitamin B6, B12 and folic acid administration did not prevent cardiovascular events in participants with or without pre‐existing cardiovascular disease. The trial sequential analysis for the same outcomes suggested that no further randomised trials were needed to assess the benefits and harms of homocysteine‐lowering interventions to preventing cardiovascular events (Figure 4; Figure 7; Figure 10). Martí‐Carvajal 2013and Martí‐Carvajal 2015 found no effect of vitamin B‐complex supplementation on rates of cancer (Figure 13). Bayes factors give prominence to these findings. There is a likelihood for reducing the stroke rate.

Quality of the evidence

We conducted GRADE assessments on outcomes using the meta‐analysed trials.

summary of findings Table 1 shows the quality of evidence for homocysteine‐lowering interventions compared with placebo or standard care for preventing cardiovascular events. The evidence available in this setting can be considered high quality due to the consistency of the results of the 12 trials for the main outcomes assessed (myocardial infarction, stroke and death from any cause), the precision in the pooled estimates, and the design and execution of these trials, which can be judged to be free of major threats to their validity.

summary of findings Table 2 shows the quality of evidence for homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose) for preventing cardiovascular events. The evidence was rated as moderate or very low due to imprecision i.e. low number of events, for risk of bias as one trial (Li 2015a) for having unclear risk of selection, conduction and detection biases, and for inconsistency (I2 = 72%).

summary of findings Table 3 shows the quality of evidence for enalapril plus folic acid compared with enalapril for adults with hypertension. The evidence for stroke was rated as high.

Potential biases in the review process

In a systematic review process, there are a group of biases called significance‐chasing biases, such as publication bias and selective outcome reporting bias (Ioannidis 2010). Selective outcome reporting bias operates through suppression of information on specific outcomes and has similarities to study publication bias in that 'negative' results remain unpublished (Ioannidis 2010). This Cochrane review found that overall, the included randomised trials had a low risk of attrition bias and a low risk of selective outcome reporting bias (Figure 2; Figure 3). This review might have a limitation due to paucity of data in terms of trials comparing 'head‐to‐head' homocysteine‐lowering interventions. A strength of this new updated Cochrane review is to have shown an absence of asymmetry in almost all funnel plots and to discard publication bias using appropriate statistical methodology i.e. Harbord and Peters tests.

Agreements and disagreements with other studies or reviews

Our results are similar to other non‐Cochrane reviews (Clarke 2010; Huang 2012; Huo 2012; Ji 2013). These four reviews differed in their eligibility criteria, i) resulting in the inclusion by Clarke 2010, Huang 2012, Huo 2012 and Ji 2013 of the HOST trial (Jamison 2007), designed to assess the effects of homocysteine in participants with kidney or renal disease, which is beyond our scope; ii) Clarke 2010 and Huo 2012 included all the trials in their pooled analysis (whereas we preferred to present the results from trials controlled with placebo separately from the results of the trials that compared different doses of homocysteine‐lowering drugs (VISP 2004)); iii) it can be concluded from the Clarke 2010 publication that the authors had access to some additional data from CHAOS 2002, which we had to extract from an abstract; and finally iv) our systematic review included five additional trials not considered in Clarke 2010, with 12,031 more participants, that allowed us to obtain more accurate estimates for our outcomes of interest (BVAIT 2009; FOLARDA 2004; GOES 2003; SU.FOL.OM3 2010; VITATOPS 2010). Lai 2015b and colleagues reported any affect on the risk of cardiovascular disease such as suggested this Cochrane review.

Two randomised controlled trials (Jamison 2007; Vianna 2007), and two systematic reviews, (Jardine 2012; Pan 2012) involving participants with end‐stage renal disease, found no effect of homocysteine‐lowering interventions in preventing cardiovascular events.

Regarding cancer, this Cochrane review showed similar results to a recent meta‐analysis involving data on 50,000 individuals (Vollset 2013). Both meta‐analyses found no increased risk of cancer associated with homocysteine‐lowering interventions.

Study flow diagram.

Figures and Tables -
Figure 1

Study flow diagram.

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

Figures and Tables -
Figure 2

Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

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Figure 3

Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on myocardial infarction. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5.95% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Figures and Tables -
Figure 4

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on myocardial infarction. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5.95% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

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Figure 5

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

Figures and Tables -
Figure 6

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.1 Myocardial infarction.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on stroke. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5% with an alpha of 5% and beta of 20%.

Figures and Tables -
Figure 7

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on stroke. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 5% with an alpha of 5% and beta of 20%.

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Figures and Tables -
Figure 8

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Figures and Tables -
Figure 9

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.2 Stroke.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on death from any cause. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 12% from proportion event in control (Pc) group of 11.7% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

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Figure 10

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on death from any cause. The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 12% from proportion event in control (Pc) group of 11.7% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Figures and Tables -
Figure 11

Funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Figures and Tables -
Figure 12

Contour‐enhanced funnel plot of comparison: 1 Homocysteine‐lowering interventions versus placebo, outcome: 1.4 Death from any cause.

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on adverse events (cancer). The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 8.49% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Figures and Tables -
Figure 13

Trial Sequential Analysis for homocysteine‐lowering interventions versus placebo on adverse events (cancer). The diversity‐adjusted required information size (DARIS) was calculated based on an expected relative risk reduction (RRR) of 10% from proportion event in control (Pc) group of 8.49% with an alpha of 5% and beta of 20%. Cumulative Z‐curve (blue line) reached futility area which means that no more trials are needed.

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 1: Myocardial infarction

Figures and Tables -
Analysis 1.1

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 1: Myocardial infarction

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 2: Stroke

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Analysis 1.2

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 2: Stroke

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 3: First unstable angina pectoris episode requiring hospitalisation

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Analysis 1.3

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 3: First unstable angina pectoris episode requiring hospitalisation

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 4: Death from any cause

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Analysis 1.4

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 4: Death from any cause

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 5: Serious adverse events (cancer)

Figures and Tables -
Analysis 1.5

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 5: Serious adverse events (cancer)

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 6: Adverse events (serious and non‐serious) excluding cancer

Figures and Tables -
Analysis 1.6

Comparison 1: Homocysteine‐lowering treatment versus other (any comparisons), Outcome 6: Adverse events (serious and non‐serious) excluding cancer

Comparison 2: Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis), Outcome 1: Myocardial infarction

Figures and Tables -
Analysis 2.1

Comparison 2: Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis), Outcome 1: Myocardial infarction

Comparison 2: Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis), Outcome 2: Stroke

Figures and Tables -
Analysis 2.2

Comparison 2: Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis), Outcome 2: Stroke

Comparison 2: Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis), Outcome 3: Death from any cause

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Analysis 2.3

Comparison 2: Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis), Outcome 3: Death from any cause

Comparison 3: Homocysteine‐lowering treatment versus placebo (Subgoup analysis), Outcome 1: Myocardial Infarction

Figures and Tables -
Analysis 3.1

Comparison 3: Homocysteine‐lowering treatment versus placebo (Subgoup analysis), Outcome 1: Myocardial Infarction

Comparison 3: Homocysteine‐lowering treatment versus placebo (Subgoup analysis), Outcome 2: Stroke

Figures and Tables -
Analysis 3.2

Comparison 3: Homocysteine‐lowering treatment versus placebo (Subgoup analysis), Outcome 2: Stroke

Comparison 3: Homocysteine‐lowering treatment versus placebo (Subgoup analysis), Outcome 3: Death

Figures and Tables -
Analysis 3.3

Comparison 3: Homocysteine‐lowering treatment versus placebo (Subgoup analysis), Outcome 3: Death

Comparison 4: Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis), Outcome 1: Myocardial infarction

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Analysis 4.1

Comparison 4: Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis), Outcome 1: Myocardial infarction

Comparison 4: Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis), Outcome 2: Stroke

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Analysis 4.2

Comparison 4: Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis), Outcome 2: Stroke

Comparison 4: Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis), Outcome 3: Death from any cause

Figures and Tables -
Analysis 4.3

Comparison 4: Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis), Outcome 3: Death from any cause

Comparison 5: Homocysteine‐lowering treatment at high dose versus low dose (Subgoup analysis), Outcome 1: Stroke

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Analysis 5.1

Comparison 5: Homocysteine‐lowering treatment at high dose versus low dose (Subgoup analysis), Outcome 1: Stroke

Comparison 6: Homocysteine‐lowering treatment (high dose) versus Homocysteine‐lowering treatment (low dose) (Sensitivity analysis), Outcome 1: Stroke

Figures and Tables -
Analysis 6.1

Comparison 6: Homocysteine‐lowering treatment (high dose) versus Homocysteine‐lowering treatment (low dose) (Sensitivity analysis), Outcome 1: Stroke

Summary of findings 1. Homocysteine‐lowering interventions (Vitamin B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin) compared with placebo or standard care for preventing cardiovascular events

Homocysteine‐lowering interventions (vitamins B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin) compared with placebo or standard care for preventing cardiovascular events

Patient or population: adults at risk of or with established cardiovascular disease
Settings: outpatients
Intervention: homocysteine‐lowering interventions (vitamins B6 (pyridoxine; pyridoxal), B9 (folic acid) or B12 (cyanocobalamin).
Comparison: placebo or standard care

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants
(studies)

Quality of the evidence
(GRADE)

Comments

Assumed risk

Corresponding risk

Placebo or standard care

Homocysteine‐lowering interventions
(vitamins B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin)

Myocardial infarction
Follow‐up: 1 to 7.3 years

60 per 1000

61 per 1000
(57 to 66)

RR 1.02
(0.95 to 1.10)

46,699
(12 trials)

⊕⊕⊕⊕
high

Stroke
Follow‐up: 1 to 7.3 years

51 per 1000

46 per 1000
(42 to 50)

RR 0.90
(0.82 to 0.99)

44,224
(10 trials)

⊕⊕⊕⊕
high

Death by any cause
Follow‐up: 1 to 7.3 years

123 per 1000

124 per 1000
(118 to 130)

RR 1.01
(0.96 to 1.06)

44,817
(11 trials)

⊕⊕⊕⊕
high

Adverse events
Follow‐up: 3.4 to 7.3 years

85 per 1000

91 per 1000
(85 to 97)

RR 1.07
(1.00 to 1.14)

35,788
(8 trials)

⊕⊕⊕⊕
high

Cancer is the only reported adverse event.

*The basis for the assumed risk (e.g. the median control group risk across studies) is the outcomes of the study control arms. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Figures and Tables -
Summary of findings 1. Homocysteine‐lowering interventions (Vitamin B6 (pyridoxine; pyridoxal); B9 (folic acid) or B12 (cyanocobalamin) compared with placebo or standard care for preventing cardiovascular events
Summary of findings 2. Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose) for preventing cardiovascular events

Homocysteine‐lowering interventions (high dose) compared with homocysteine lowering interventions (low dose) for preventing cardiovascular events

Patient or population: adults at risk of or with established cardiovascular disease
Settings: outpatients
Intervention: homocysteine‐lowering interventions (high dose) either (folic acid; vitamin B12 (cyanocobalamin) and vitamin B6 (pyridoxine; pyridoxal) or folic acid
Comparison: homocysteine‐lowering interventions (low dose) either (folic acid; vitamin B12; vitamin B6 per day) or folic acid

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants
(studies)

Quality of the evidence
(GRADE)

Comments

Assumed risk

Corresponding risk

Homocysteine‐lowering interventions (low‐dose)

Homocysteine‐lowering interventions (high‐dose)

Myocardial infarction
Follow‐up: 2 years

44 per 1000

40 per 1000
(29 to 54)

RR 0.90
(0.66 to 1.23)

3649
(1 trial)

⊕⊕⊕⊝
moderate1

VISP 2004:

  • High dose (2.5 mg folic acid; 0.4 mg vitamin B12 (cyanocobalamin) and 25 mg vitamin B6 (pyridoxine; pyridoxal)

  • Low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6 per day).

Stroke
Follow‐up: 2 to 5 years

112 per 1000

101 per 1000
(74 to 137)

RR 0.90
(0.66 to 1.22)

3929
(2 trials)

⊕⊝⊝⊝
very low1, 2, 3

1. Li 2015a was conducted including only Chinese elderly females.Trial used only folic acid as homocysteine‐lowering intervention.

  • High‐dose folic acid (0.8 mg/d)

  • Low‐dose folic acid (0.4 mg/d))

2. VISP 2004:

  • High dose (2.5 mg folic acid; 0.4 mg vitamin B12 (cyanocobalamin) and 25 mg vitamin B6 (pyridoxine; pyridoxal)

  • Low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6 per day).

Death by any cause
Follow‐up: 2 years

64 per 1000

55 per 1000
(42 to 71)

RR 0.86
(0.66 to 1.11)

3649
(1 trial)

⊕⊕⊕⊝
moderate1

VISP 2004:

  • High dose (2.5 mg folic acid; 0.4 mg vitamin B12 (cyanocobalamin) and 25 mg vitamin B6 (pyridoxine; pyridoxal)

  • Low dose (20 micrograms folic acid; 6 micrograms vitamin B12; 200 micrograms vitamin B6 per day).

Cancer

Not estimable

Li 2015a and VISP 2004 reported no information on this outcome.

*The basis for the assumed risk (e.g. the median control group risk across studies) is the outcomes of the study control arms. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

1 Downgraded one level for imprecision due to low number of events
2 Dowgraded one level for risk of bias as one trial (Li 2015a) was rated as having unclear risk of selection, conduction and detection biases
3 Downgraded one level for heterogeneity (I‐squared: 72%).

Figures and Tables -
Summary of findings 2. Homocysteine‐lowering interventions (high dose) compared with homocysteine‐lowering interventions (low dose) for preventing cardiovascular events
Summary of findings 3. Enalapril plus folic acid compared with enalapril for adults with hypertension

Enalapril plus folic acid compared with folic acid for adults with hypertension

Patient or population: adults with hypertension
Settings: Chinese outpatients
Intervention: enalapril (10 mg) plus folic acid (0.8 mg)
Comparison: enalapril (10 mg)

Outcomes

Illustrative comparative risks* (95% CI)

Relative effect
(95% CI)

No of Participants
(studies)

Quality of the evidence
(GRADE)

Comments

Assumed risk

Corresponding risk

Folic acid

Enalapril plus folic acid

Myocardial infarction
Follow‐up: median 4.5 years

2 per 1000

2 per 1000
(1 to 4)

RR 1.04
(0.60 to 1.82)

20,702
(1 trial)

⊕⊕⊕⊝
moderate1

Stroke
Follow‐up: median 4.5 years

34 per 1000

27 per 1000
(23 to 32)

RR 0.79
(0.68 to 0.93)

20,702
(1 trial)

⊕⊕⊕⊕
high

First unstable angina pectoris episode requiring hospitalisation

Not estimable

CSPPT 2015 did not assess this outcome.

Death from any cause
Follow‐up: median 4.5 years

31 per 1000

29 per 1000
(25 to 34)

RR 0.94
(0.81 to 1.10)

20,702
(1 trial)

⊕⊕⊕⊕
high

Serious adverse event (cancer)
Follow‐up: median 4.5 years

8 per 1000

8 per 1000
(6 to 11)

RR 0.96
(0.71 to 1.31)

20,243
(1 trial)

⊕⊕⊕⊝
moderate1

CSPPT 2015 included either neoplasms benign, malignant or unspecified

*The basis for the assumed risk (e.g. the median control group risk across studies) is the outcomes of the study control arms. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: Confidence interval; RR: Risk ratio;

GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

1Downgraded one level for imprecision due to low number of events.

Figures and Tables -
Summary of findings 3. Enalapril plus folic acid compared with enalapril for adults with hypertension
Comparison 1. Homocysteine‐lowering treatment versus other (any comparisons)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

1.1 Myocardial infarction Show forest plot

14

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

1.1.1 Homocysteine‐lowering versus placebo

12

46699

Risk Ratio (M‐H, Random, 95% CI)

1.02 [0.95, 1.10]

1.1.2 Homocysteine‐lowering treatment at high dose versus low dose

1

3649

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.66, 1.23]

1.1.3 Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

1

20702

Risk Ratio (M‐H, Random, 95% CI)

1.04 [0.60, 1.82]

1.2 Stroke Show forest plot

13

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

1.2.1 Homocysteine‐lowering treatment versus placebo

10

44224

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.82, 0.99]

1.2.2 Homocysteine‐lowering treatment at high dose versus low dose

2

3929

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.66, 1.22]

1.2.3 Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

1

20702

Risk Ratio (M‐H, Random, 95% CI)

0.79 [0.68, 0.93]

1.3 First unstable angina pectoris episode requiring hospitalisation Show forest plot

4

12644

Risk Ratio (M‐H, Random, 95% CI)

0.98 [0.80, 1.21]

1.4 Death from any cause Show forest plot

13

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

1.4.1 Homocysteine‐lowering treatment versus placebo

11

44817

Risk Ratio (M‐H, Random, 95% CI)

1.01 [0.96, 1.06]

1.4.2 Homocysteine‐lowering treatments at high dose versus low dose

1

3649

Risk Ratio (M‐H, Random, 95% CI)

0.86 [0.66, 1.11]

1.4.3 Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

1

20702

Risk Ratio (M‐H, Random, 95% CI)

0.94 [0.81, 1.10]

1.5 Serious adverse events (cancer) Show forest plot

9

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

1.5.1 Homocysteine‐lowering versus placebo

8

35788

Risk Ratio (M‐H, Random, 95% CI)

1.07 [1.00, 1.14]

1.5.2 Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril)

1

20243

Risk Ratio (M‐H, Random, 95% CI)

0.96 [0.71, 1.31]

1.6 Adverse events (serious and non‐serious) excluding cancer Show forest plot

3

13802

Risk Ratio (M‐H, Random, 95% CI)

1.02 [0.88, 1.19]

1.6.1 Homocysteine‐lowering versus placebo

3

13802

Risk Ratio (M‐H, Random, 95% CI)

1.02 [0.88, 1.19]

Figures and Tables -
Comparison 1. Homocysteine‐lowering treatment versus other (any comparisons)
Comparison 2. Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

2.1 Myocardial infarction Show forest plot

6

37442

Risk Ratio (M‐H, Random, 95% CI)

1.01 [0.94, 1.09]

2.1.1 Trials with low risk of bias

6

37442

Risk Ratio (M‐H, Random, 95% CI)

1.01 [0.94, 1.09]

2.2 Stroke Show forest plot

6

37442

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.80, 1.02]

2.2.1 Trials with low risk of bias

6

37442

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.80, 1.02]

2.3 Death from any cause Show forest plot

7

37932

Risk Ratio (M‐H, Random, 95% CI)

1.03 [0.95, 1.12]

2.3.1 Trials with low risk of bias

7

37932

Risk Ratio (M‐H, Random, 95% CI)

1.03 [0.95, 1.12]

Figures and Tables -
Comparison 2. Homocysteine‐lowering treatment versus placebo or standard care (Sensitivity analysis)
Comparison 3. Homocysteine‐lowering treatment versus placebo (Subgoup analysis)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

3.1 Myocardial Infarction Show forest plot

12

46699

Risk Ratio (M‐H, Random, 95% CI)

1.02 [0.95, 1.10]

3.1.1 Without history of cardiovascular disease

1

490

Risk Ratio (M‐H, Random, 95% CI)

0.98 [0.14, 6.87]

3.1.2 With history of cardiovascular disease

11

46209

Risk Ratio (M‐H, Random, 95% CI)

1.02 [0.95, 1.10]

3.2 Stroke Show forest plot

10

44224

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.82, 0.99]

3.2.1 Without history of cardiovascular disease

1

490

Risk Ratio (M‐H, Random, 95% CI)

0.20 [0.01, 4.04]

3.2.2 With history of cardiovascular disease

9

43734

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.82, 0.99]

3.3 Death Show forest plot

11

44817

Risk Ratio (M‐H, Random, 95% CI)

1.01 [0.96, 1.06]

3.3.1 Without history of cardiovascular disease

1

490

Risk Ratio (M‐H, Random, 95% CI)

0.20 [0.01, 4.04]

3.3.2 With history of cardiovascular disease

10

44327

Risk Ratio (M‐H, Random, 95% CI)

1.01 [0.96, 1.06]

Figures and Tables -
Comparison 3. Homocysteine‐lowering treatment versus placebo (Subgoup analysis)
Comparison 4. Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

4.1 Myocardial infarction Show forest plot

1

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

4.1.1 Per protocol analysis

1

20635

Risk Ratio (M‐H, Random, 95% CI)

1.04 [0.60, 1.82]

4.1.2 Best‐worst scenario

1

20702

Risk Ratio (M‐H, Random, 95% CI)

0.42 [0.27, 0.68]

4.1.3 Worst‐best scenario

1

20702

Risk Ratio (M‐H, Random, 95% CI)

2.38 [1.48, 3.83]

4.2 Stroke Show forest plot

1

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

4.2.1 Per protocol analysis

1

20635

Risk Ratio (M‐H, Random, 95% CI)

0.79 [0.68, 0.93]

4.2.2 Best‐worst scenario

1

20702

Risk Ratio (M‐H, Random, 95% CI)

0.72 [0.62, 0.84]

4.2.3 Worst‐best scenario

1

20702

Risk Ratio (M‐H, Random, 95% CI)

0.88 [0.76, 1.03]

4.3 Death from any cause Show forest plot

1

Risk Ratio (M‐H, Random, 95% CI)

Subtotals only

4.3.1 Per protocol analysis

1

20635

Risk Ratio (M‐H, Random, 95% CI)

0.94 [0.81, 1.10]

4.3.2 Best‐worst scenario

1

20702

Risk Ratio (M‐H, Random, 95% CI)

0.85 [0.73, 0.99]

4.3.3 Worst‐best scenario

1

20702

Risk Ratio (M‐H, Random, 95% CI)

1.04 [0.90, 1.21]

Figures and Tables -
Comparison 4. Homocysteine‐lowering treatment (folic acid) plus antihypertensive therapy (enalapril) versus antihypertensive therapy (enalapril) (Sensitivity analysis)
Comparison 5. Homocysteine‐lowering treatment at high dose versus low dose (Subgoup analysis)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

5.1 Stroke Show forest plot

2

3929

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.66, 1.22]

5.1.1 Combined (folic acid, vitamin B6 and vitamin B12)

1

3649

Risk Ratio (M‐H, Random, 95% CI)

1.04 [0.84, 1.29]

5.1.2 Folic acid alone

1

280

Risk Ratio (M‐H, Random, 95% CI)

0.76 [0.59, 0.98]

Figures and Tables -
Comparison 5. Homocysteine‐lowering treatment at high dose versus low dose (Subgoup analysis)
Comparison 6. Homocysteine‐lowering treatment (high dose) versus Homocysteine‐lowering treatment (low dose) (Sensitivity analysis)

Outcome or subgroup title

No. of studies

No. of participants

Statistical method

Effect size

6.1 Stroke Show forest plot

2

3929

Risk Ratio (M‐H, Random, 95% CI)

0.90 [0.66, 1.22]

6.1.1 Trials with low risk of bias

1

3649

Risk Ratio (M‐H, Random, 95% CI)

1.04 [0.84, 1.29]

6.1.2 Trials with high risk of bias

1

280

Risk Ratio (M‐H, Random, 95% CI)

0.76 [0.59, 0.98]

Figures and Tables -
Comparison 6. Homocysteine‐lowering treatment (high dose) versus Homocysteine‐lowering treatment (low dose) (Sensitivity analysis)