Introduction
Methods
Search strategy
Inclusion criteria
Exclusion criteria
Study selection and data extraction
Primary and secondary outcome variables
Risk of bias assessment
Statistical analysis
Results
Characteristics of included studies
Author, year | Design | Participants, n | Diabetes Type | Age, yeara | Intervention | Duration (week) | Outcomes (changes)b | Adjust/matching3 | ||
---|---|---|---|---|---|---|---|---|---|---|
Treatment group | Control group | Treatment group | Control group | |||||||
Koay et al. 2021 [14] | RA/PC/DB / PA | M/F: 59: Int: 31, Con: 28 | Diabetic nephropathy | Int: 66 ± 13, Con:70 ± 13 | 400 mg/d tocotrienol-Rich Vitamin E | Placebo: NR | 52 | HbA1c: 0.16 ± 0.86% | HbA1c: 0.42 ± 0.74% | Gender, duration of diabetes, baseline HbA1c |
Tat-Ng et al. 2020 | RA/PC/DB / PA | M/F: 80: Int: 39, Con: 41 | Diabetic neuropathy | Int: 63 ± 12, Con:64 ± 15 | 400 mg/d tocotrienol-Rich Vitamin E | Placebo: NR | 8 | HbA1c: 0.23 ± 1.05% | HbA1c: 0.41 ± 1.12% | |
Dalan et al. 2020 [24] | RA/PC/DB / PA | M/F: 166: Int: 84, Con: 82 | T2DM | Int: 55 ± 10, Con: 57 ± 10 | 266 mg/d α-tocopherol | Placebo: NR | 24 | HbA1c: -0.08 ± 0.73% | HbA1c: -0.03 ± 0.82% | Baseline alpha-tocopherol, haptoglobin genotype |
Jie-Tan et al. 2019 | RA/PC/DB / PA | M/F: 54: Int: 27, Con: 27 | Diabetic nephropathy | Int: 59 ± 10, Con:62 ± 11 | 400 mg/d tocotrienol-Rich Vitamin E | Placebo: NR | 12 | HbA1c: -0.6 ± 0.95% | HbA1c: -0.38 ± 0.89% | Gender, duration of diabetes, baseline HbA1c |
Bril et al. 2019 [23] | RA/PC/DB / PA | M/F: 68: Int: 36, Con: 32 | T2DM | Int: 60 ± 9, Con:57 ± 11 | 720 mg/d vitamin E | Placebo: NR | 77 | Insulin: -3.0 ± 6.0 µIU/mL FBG: -3.0 ± 39.0 mg/dL HbA1c: -0.3 ± 1.2% | Insulin: 3.0 ± 12.0 µIU/mL FBG: 6.0 ± 53.0 mg/dL HbA1c: 0.3 ± 1.6% | |
El-Aal et al. 2018 [26] | RA/PC/SB/ PA | M: 20: Int: 10, Con: 10 | T2DM | Int: 51, Con: 51 | 400 mg/d α-tocopherol + metformin | Placebo: metformin | 12 | Insulin: -3.8 ± 3.4 µIU/mL FBG: -23.1 ± 13.6 mg/dL HbA1c: -0.9 ± 1.2% HOMA: -4.7 ± 1.1 | Insulin: 1.7 ± 5.0 µIU/mL FBG: 14.2 ± 23.6 mg/dL HbA1c: 0.06 ± 0.8% HOMA: 1.5 ± 2.7 | |
M: 20: Int: 10, Con: 10 | T2DM | Int: 51, Con: 51 | 400 mg/d α-tocopherol + metformin + vitamin C | Placebo: metformin + vitamin C | 12 | Insulin: -5.0 ± 5.3 µIU/mL FBG: -29.2 ± 33.0 mg/dL HbA1c: -1.0 ± 0.8% HOMA: -4.5 ± 1.2 | Insulin: -4.3 ± 2.9 µIU/mL FBG: -24.5 ± 23.1 mg/dL HbA1c: -0.7 ± 0.6% HOMA: -2.3 ± 1.2 | |||
Tan et al. 2018 | RA/PC/DB / PA | M/F: 45: Int: 22, Con: 23 | T2DM | Int: 59 ± 10, Con:63 ± 10 | 400 mg/d tocotrienol-rich vitamin E | Placebo: NR | 8 | HbA1c: -0.55 ± 1.8% | HbA1c: -0.09 ± 1.3% | Age, baseline values |
Dass et al. 2018 [25] | RA/PA | M/F: 60: Int: 31, Con: 29 | T2DM | Int: 51 ± 9, Con:51 ± 7 | 400 mg/d vitamin E | Placebo: NR | 12 | FBG: -16.8 ± 18.3 mg/dL HbA1c: -0.19 ± 0.40% | FBG: -11.5 ± .19.2 mg/dL HbA1c: -0.31 ± 0.49% | |
Rafraf et al. 2016 [28] | RA/PC/DB / PA | M/F: 83: Int: 42, Con: 41 | T2DM | Int: 53 ± 6, Con:53 ± 8 | 360 mg/d α-tocopherol | Placebo: NR | 8 | Insulin: -1.3 ± 2.4 µIU/mL FBG: -9.1 ± 20.8 mg/dL HbA1c: -0.31 ± 0.67% HOMA: -0.66 ± 0.85 | Insulin: -0.91 ± 2.90 µIU/mL FBG: 4.5 ± 19.1 mg/dL HbA1c: -0.19 ± 0.77% HOMA: -0.19 ± 1.13 | Gender, Age, BMI, medication,FBS level |
Stonehouse et al. 2016 [18] | RA/PC/DB / PA | M/F: 57: Int: 28, Con: 29 | T2DM | Int: 60 ± 6, Con:61 ± 5 | 1020 mg/d α-tocopherol | Placebo: Palm olein | 8 | Insulin: -1.6 ± 0.7 µIU/mL FBG: -5.4 ± 13.8 mg/dL HbA1c: 0.02 ± 0.35% HOMA: -0.21 ± 0.57 | Insulin: -0.78 ± 0.99 µIU/mL FBG: -1.9 ± 13.6 mg/dL HbA1c: 0.04 ± 0.34% HOMA: -0.11 ± 0.54 | |
Keihan et al. 2016 [44] | RA/PC/DB / PA | M/F: 68: Int: 32, Con: 36 | DM | Int: 57 ± 6, Con:61 ± 6 | 150 mg/d α-tocopherol | Placebo: NR | 12 | FBG: -7.1 ± 12.3 mg/dL HbA1c: 0.54 ± 0.25% | FBG: -21.0 ± .7.1 mg/dL HbA1c: 0.4 ± 0.18% | |
Khatami et al. 2016 [17] | RA/PC/DB / PA | M/F: 60: Int: 30, Con: 30 | Diabetic nephropathy | Int: 61 ± 10, Con:62 ± 13 | 804 mg/d vitamin E | Placebo: NR | 12 | Insulin: -0.50 ± 2.19 µIU/mL FBG: 11.7 ± 31.2 mg/dL HOMA: 0.10 ± 1.64 | Insulin: 0.70 ± 2.19 µIU/mL FBG: 1.7 ± 31.2 mg/dL HOMA: 0.30 ± 1.64 | Gender, Age, medications, duration of diabetes, baseline BMI |
Hejazi et al. 2015 [27] | RA/PC/SB / PA | M/F: 27: Int: 14, Con: 13 | T2DM | Int: 48 ± 6, Con:46 ± 7 | 360 mg/d vitamin E | Placebo: NR | 6 | Insulin: 0.2 ± 3.3 µIU/mL FBG: -8.5 ± 42.5 mg/dL HOMA: 0.01 ± 1.22 | Insulin: 2.7 ± 4.6 µIU/mL FBG: -16.0 ± 26.7 mg/dL HOMA: 0.06 ± 1.69 | |
Hashemi et al. 2014 [21] | RA/PC/DB / PA | M/F: 66: Int: 32, Con: 36 | T2DM | Int: 44 ± 4, Con:45 ± 4 | 360 mg/d α-tocopherol acetate | Placebo: NR | 12 | Insulin: 0.3 ± 2.5 µIU/mL FBG: 36.1 ± 39.6 mg/dL HbA1c: 0.20 ± 0.85% HOMA: 0.50 ± 1.02 | Insulin: 1.5 ± 2.8 µIU/mL FBG: 4.7 ± 35.1 mg/dL HbA1c: 0.2 ± 1.11% HOMA: 0.70 ± 1.15 | |
M/F: 68: Int: 34, Con: 34 | T2DM | Int: 45 ± 4, Con:44 ± 5 | 360 mg/d α-tocopherol acetate + EPA | Placebo + EPA | 12 | Insulin: -1.6 ± 2.4 µIU/mL FBG: -10.1 ± 31.7 mg/dL HbA1c: -0.6 ± 0.85% HOMA: -0.7 ± 1.08 | Insulin: -0.6 ± 3.6 µIU/mL FBG: -19.5 ± 23.2 mg/dL HbA1c: -0.8 ± 0.79% HOMA: -0.6 ± 1.26 | |||
Shadman et al. 2013 [12] | RA/PC/DB / PA | M/F: 46: Int: 17, Con: 29 | Overweight T2DM | Int: 47 ± 4, Con:45 ± 6 | 90 mg/d vitamin E + CLA | Placebo: CLA | 8 | Insulin: -0.30 ± 4.15 µIU/mL FBG: -4.2 ± 10.7 mg/dL HbA1c: -0.50 ± 1.00% HOMA: -0.27 ± 1.94 | Insulin: 0.50 ± 2.09 µIU/mL FBG: 2.7 ± 12.5 mg/dL HbA1c: -1.01 ± 1.04% HOMA: -0.7 ± 1.70 | Body composition |
Rafraf et al. 2012 [11] | RA/PC/DB / PA | M/F: 83: Int: 42, Con: 41 | T2DM | Int: 35 ± 6, Con:35 ± 8 | 400 mg/d α-tocopherol acetate | Placebo: NR | 8 | FBG: -9.1 ± 21.3 mg/dL | FBG: 4.5 ± 19.4 mg/dL | Gender, Age, BMI, duration of diabetes, baseline values |
Udupa et al. 2012 [13] | RA/PC/DB / PA | M/F: 50: Int: 25, Con: 25 | T2DM | Int: 53 ± 2, Con:53 ± 2 | 400 mg/d vitamin E | Placebo: NR | 12 | FBG: -6.2 ± 14.4 mg/dL HbA1c: -1.54 ± 1.14% | FBG: 4.9 ± 14.6 mg/dL HbA1c: -0.41 ± 1.16% | |
Vijayakumar et al. 2011 | RA/ PA | M/F: 74 Int: 38, Con: 36 | T2DM | Int: 54 ± 8, Con:56 ± 8 | 600 mg/d vitamin E | Placebo: NR | 13 | HbA1c: -1.16 ± 0.77% | HbA1c: -0.99 ± 0.77% | |
Oliveira et al. 2011 [45] | RA/PC/DB / PA | M/F: 51 Int: 25, Con: 26 | T2DM | 30–79 | 800 mg/d α-tocopherol | Placebo: NR | 17 | Insulin: 0.80 ± 5.69 µIU/mL FBG: -1.0 ± 34.94 mg/dL HOMA: 0.40 ± 1.98 | Insulin: 0.00 ± 4.84 µIU/mL FBG: -0.30 ± 46.49 mg/dL HOMA: -0.20 ± 2.32 | |
M/F: 51 Int: 25, Con: 26 | T2DM | 30–79 | 800 mg/d α-tocopherol + lipoic acid | Placebo + lipoic acid | 17 | Insulin: 2.1 ± 4.7 µIU/mL FBG: -17.7 ± 42.5 mg/dL HOMA: 0.10 ± 1.26 | Insulin: -0.9 ± 6.69 µIU/mL FBG: -13.2 ± 57.9 mg/dL HOMA: -0.6 ± 3.51 | |||
Giannini et al. 2007 [46] | RA/PC/DB/ CO | M/F: 10 Int: 10, Con: 10 | T1DM | Int: 18 ± 3, Con: 18 ± 3 | 1200 mg/d α-tocopherol | Placebo: NR | 24 | HbA1c: -0.04 ± 0.37% | HbA1c: -0.02 ± 0.78% | |
Winterbone et al. 2007 [47] | RA/PC/ PA | M/F: 19 Int: 10, Con: 9 | T2DM | Int: 62 ± 5, Con: 61 ± 5 | 1080 mg/d α-tocopherol | Placebo: NR | 4 | Insulin: 6.6 ± 19.2 µIU/mL FBG: -9.0 ± 32.6 mg/dL | Insulin: -1.0 ± 14.1 µIU/mL FBG: 1.8 ± 13.5 mg/dL | |
Ward et al. 2007 [19] | RA/PC/DB / PA | M/F: 36 Int: 18, Con: 18 | T2DM | Int: 64 ± 29, Con: 62 ± 29 | 500 mg/d α-tocopherol | Placebo: NR | 6 | Insulin: 1.1 ± 3.3 µIU/mL FBG: -3.6 ± 26.0 mg/dL | Insulin: -1.3 ± 6.2 µIU/mL FBG: -1.7 ± 28.1 mg/dL | Blood pressure |
M/F: 37 Int: 19, Con: 18 | Int: 58 ± 17, Con: 62 ± 29 | 500 mg/d mixed tocopherols | Placebo: NR | Insulin: -0.10 ± 4.56 µIU/mL FBG: 7.2 ± 33.2 mg/dL | Insulin: -1.30 ± 6.20 µIU/mL FBG: -1.7 ± 28.1 mg/dL | |||||
Baliarsingh et al. 2005 [48] | RA/PC/DB/ CO | M/F: 19 Int: 19, Con: 19 | T2DM | Int: 48 ± 6, Con: 52 ± 6 | 180 mg/d α-tocopherol | Placebo: NR | 8 | FBG: 1.4 ± 10.1 mg/dL HbA1c: 0.00 ± 0.25% | FBG: 5.9 ± 13.0 mg/dL HbA1c: 0.00 ± 0.25% | |
Boshtam et al. 2005 [49] | RA/PC/TB / PA | M/F: 100 Int: 50, Con: 50 | T2DM | Int: 52 ± 9, Con: 54 ± 7 | 134 mg/d α-tocopherol | Placebo: NR | 27 | Insulin: 2.5 ± 6.9 µIU/mL FBG: -8.5 ± 36.9 mg/dL HbA1c: -0.40 ± 0.96% | Insulin: 2.1 ± 5.5 µIU/mL FBG: -27.0 ± 59.3 mg/dL HbA1c: 0.10 ± 1.01% | Gender, age, education, occupation |
Ble-Castillo et al. 2005 [20] | RA/PC/PA | F: 34:: Int: 13, Con: 21 | T2DM | Int: 51 ± 14, Con: 55 ± 11 | 800 mg/d α-tocopherol | Placebo: NR | 6 | FBG: 17.1 ± 14.5 mg/dL | FBG: -32.9 ± 53.8 mg/dL | |
Economides et al. 2005 [50] | RA/PC/ DB/ PA | M/F: 66: Int: 34, Con: 32 | T2DM | Int: 53 ± 14, Con: 53 ± 14 | 1080 mg/d vitamin E | Placebo: NR | 52 | HbA1c: 0.00 ± 0.74% | HbA1c: 0.00 ± 0.66% | |
Manzella et al. 2001 [51] | RA/PC/DB / PA | M/F: 50: Int: 25, Con: 25 | T2DM | Int: 63 ± 5, Con: 65 ± 4 | 600 mg/d α-tocopherol | Placebo: NR | 17 | Insulin: -11.1 ± 0.1 µIU/mL FBG: -1.8 ± 3.1 mg/dL HbA1c: -0.70 ± 0.18% HOMA: -0.53 ± 0.23 | Insulin: -0.4 ± 0.1 µIU/mL FBG: -1.8 ± 2.4 mg/dL HbA1c: -0.10 ± 0.36% HOMA: -0.01 ± 0.13 | |
Park et al. 2001 | RA/PC/PA | M/F: 98 Int: 58, Con: 40 | T2DM | Int: 49 ± 9, Con: 49 ± 10 | 200 mg/d α-tocopherol + CSII | Placebo: CSII | 8 | Insulin: 6.1 ± 3.5 µIU/mL FBG: -91.8 ± 80.1 mg/dL HbA1c: -3.5 ± 1.3% | Insulin: 7.9 ± 1.3 µIU/mL FBG: -88.2 ± .65.3 mg/dL HbA1c: -3.3 ± 1.3% | |
Feng et al. 2000 [52] | RA/PC/DB/ CO | M/F: 20 Int: 20, Con: 20 | T2DM | Int: 32 ± 8, Con: 32 ± 8 | 1620 mg/d vitamin E | Placebo: NR | 17 | HbA1c: 0.33 ± 0.80% | HbA1c: 0.18 ± 0.87% | |
Bursell et al. 1999 [53] | RA/PC/DB/ CO | M/F: 36 Int: 36, Con: 36 | DM1 | Int: 31 ± 7, Con: 31 ± 7 | 1206 mg/d vitamin E | Placebo: NR | 36 | FBG: -17.2 ± 65.1 mg/dL HbA1c: 0.20 ± 1.02% | FBG: -31.7 ± 62.3 mg/dL HbA1c: 0.20 ± 1.27% | |
Gazis et al. 1999 [54] | RA/PC/DB / PA | M/F: 48 Int: 23, Con: 25 | T2DM | Int: 56 ± 11, Con: 57 ± 11 | 1440 mg/d α-tocopherol | Placebo: NR | 8 | FBG: 2.3 ± 33.7 mg/dL HbA1c: 0.20 ± 0.98% | FBG: 5.4 ± 36.7 mg/dL HbA1c: 0.00 ± 0.67% | |
Tutuncu et al. 1998 | RA/PC/DB / PA | M/F: 48 Int: 23, Con: 25 | T2DM | Int: 56 ± 11, Con: 57 ± 11 | 900 mg/d vitamin E | Placebo: NR | 24 | FBG: 9.0 ± 24.1 mg/dL HbA1c: -1.80 ± 1.07% | FBG: 7.2 ± 11.7 mg/dL HbA1c: 1.10 ± 2.02% | Age, duration of disease, metabolic control |
Colette et al. 1998 | RA/PC/DB/ CO | M/F: 9 Int: 9, Con: 9 | T1DM | Int: 51 ± 11, Con: 51 ± 11 | 1000 mg/d vitamin E | Placebo: NR | 5 | HbA1c: 0.00 ± 0.94% | HbA1c: 0.70 ± 1.36% | Age, gender, weight |
Duntas et al. 1996 [55] | RA/PC/PA | M/F: 24: Int: 12, Con: 12 | T1DM | Int: 41 ± 12, Con:39 ± 12 | 360 mg/d α-tocopherol | Placebo: NR | 26 | FBG: -1.8 ± 19.7 mg/dL HbA1c: -0.12 ± 0.51% | FBG: 0.0 ± 19.7 mg/dL HbA1c: 0.7 ± 0.80% | Duration of disease, weight, glycemic control, insulin dose |
M/F: 24: Int: 12, Con: 12 | 720 mg/d α-tocopherol | Placebo: NR | FBG: -3.6 ± 18.7 mg/dL HbA1c: -0.56 ± 0.46% | FBG: 0.0 ± 19.7 mg/dL HbA1c: 0.7 ± 0.80% | ||||||
Fuller et al. 1996 [56] | RA/PC/PA | M/F: 30 Int: 15, Con: 15 | T1DM | Int: 47 ± 14, Con: 47 ± 12 | 1080 mg/d α-tocopherol | Placebo: NR | 8 | FBG: 27.0 ± 68.0 mg/dL HbA1c: -0.30 ± 1.14% | FBG: 27.0 ± 46.5 mg/dL HbA1c: 0.40 ± 1.59% | |
Reaven et al. 1995 [57] | RA/PC/DB / PA | M: 21: Int: 10, Con: 11 | T2DM | Int: 60 ± 6, Con:61 ± 8 | 1440 mg/d α-tocopherol | Placebo: NR | 10 | FBG: -0.72 ± 22.76 mg/dL HbA1c: 0.20 ± 0.67% | FBG: -2.1 ± 21.3 mg/dL HbA1c: 0.00 ± 0.66% | |
Paolisso et al. 1993 [10] | RA/PC/DB/ CO | NR: 25: Int: 25, Con: 25 | T2DM | Int: 71, Con:71 | 900 mg/d d-a-tocopherol Ephynal | Placebo: NR | 12 | FBG: -12.6 ± 24.1 mg/dL HbA1c: -0.60 ± 1.58% | FBG: 1.8 ± 21.6 mg/dL HbA1c: 0.10 ± 1.58% | |
Ceriello et al. 1991 [7] | RA/PC/PA | M/F: 20: Int: 10, Con: 10 | T2DM | Int: 41 ± 4, Con:40 ± 4 | 1200 mg/d vitamin E | Placebo: NR | 8 | FBG: 9.0 ± 43.1 mg/dL HbA1c: -4.3 ± 1.3% | FBG: -1.8 ± 41.9 mg/dL HbA1c: -0.10 ± 1.39% | Age, duration of disease, metabolic control |
T2DM | Int: 42 ± 3, Con:40 ± 4 | 600 mg/d vitamin E | Placebo: NR | FBG: 10.8 ± 45.3 mg/dL HbA1c: -2.9 ± 1.9% | FBG: -1.8 ± 41.99 mg/dL HbA1c: -0.10 ± 1.39% |
Findings from the systematic review
Findings from the meta-analysis
Vitamin E and fasting blood glucose
Effect size, n | WMD (95% CI)a | P-within2 | Ib (%)c | P-heterogeneityd | |
---|---|---|---|---|---|
Vitamin E intake on fasting blood glucose | |||||
Overall | 34 | -3.35 (-8.10, 1.40) | 0.16 | 82.2 | < 0.001 |
Intervention duration (week) | |||||
< 10 | 15 | -6.04 (-9.88, -2.21) | 0.002 | 19.1 | 0.24 |
≥ 10 | 19 | -2.86 (-10.39, 4.66) | 0.45 | 89 | < 0.001 |
Type of vitamin E | |||||
α-tocopherol | 21 | -3.75 (-11.21, 3.71) | 0.32 | 88.4 | < 0.001 |
Tocoterienol | 2 | -4.44 (-8.91, 0.03) | 0.05 | 0.0 | 0.62 |
Mixed-tocopherols | 1 | 9.00 (-14.72, 32.71) | 0.45 | 0.0 | - |
Unclear | 10 | -5.24 (-9.59, -0.88) | 0.01 | 3.3 | 0.40 |
Dosage of vitamin E (mg/day) | |||||
< 500 | 15 | -7.13 (-14.99, 0.73) | 0.07 | 87.3 | < 0.001 |
≥ 500 | 19 | -0.22 (-1.73, 1.29) | 0.77 | 0.0 | 0.55 |
Study location | |||||
Western countries | 16 | -0.33 (-1.85, 1.19) | 0.67 | 0.0 | 0.52 |
Non-Western countries | 18 | -4.53 (-11.59, 2.53) | 0.20 | 85.1 | < 0.001 |
Study design | |||||
Crossover | 3 | -7.07 (-15.46, 1.32) | 0.09 | 30.1 | 0.23 |
Parallel | 31 | -2.82 (-8.08, 2.44) | 0.29 | 83.4 | < 0.001 |
Blinded | 25 | -3.96 (-9.39, 1.47) | 0.15 | 86.5 | < 0.001 |
Non-blinded | 9 | -2.81 (-9.62, 3.99) | 0.41 | 0 | 0.49 |
Type of diabetes | |||||
T2DM | 27 | -4.42 (-9.63, 0.76) | 0.09 | 85 | < 0.001 |
T1DM | 6 | 0.87 (-10.53, 12.27) | 0.88 | 0.0 | 0.94 |
Diabetic nephropathy | 1 | 10.00 (-5.80, 25.80) | 0.21 | 0.0 | |
Risk of bias e | |||||
High | 28 | -4.10 (-9.81, 1.61) | 0.16 | 83.2 | < 0.001 |
Low | 6 | 0.04 (-9.71, 9.78) | 0.994 | 79.7 | < 0.001 |
Vitamin E intake on HbA1c | |||||
Overall | 36 | -0.21 (-0.33, -0.09) | 0.001 | 76.6 | < 0.001 |
Intervention duration (week) | |||||
< 10 | 13 | -0.24 (-0.48, 0.00) | 0.05 | 75.3 | < 0.001 |
≥ 10 | 23 | -0.24 (-0.48, 0.00) | 0.01 | 78.2 | < 0.001 |
Type of vitamin E | |||||
α-tocopherol | 19 | -0.18 (-0.36, 0.01) | 0.06 | 76.3 | < 0.001 |
Tocoterienol | 6 | -0.09 (-0.15, -0.04) | < 0.001 | 0.0 | 0.81 |
unclear | 11 | -0.71 (-1.21, -0.21) | 0.005 | 86 | < 0.001 |
Dosage of Vitamin E (mg/day) | |||||
≥ 500 | 18 | -0.41 (-0.68, -0.14) | 0.003 | 80.2 | < 0.001 |
< 500 | 18 | -0.10 (-0.22, 0.02) | 0.09 | 62.2 | < 0.001 |
Study location | |||||
Western countries | 16 | -0.40 (-0.69, -0.11) | 0.007 | 79.5 | < 0.001 |
Non-Western countries | 20 | -0.12 (-0.24, 0.00) | 0.05 | 66.5 | < 0.001 |
Study design | |||||
Crossover | 6 | -0.09 (-0.15, -0.04) | 0.001 | 0 | 0.54 |
Parallel | 30 | -0.26 (-0.43, -0.10) | 0.002 | 80.1 | < 0.001 |
Blinded | 27 | -0.16 (-0.29, -0.04) | 0.01 | 74.8 | < 0.001 |
Non-blinded | 9 | -0.68 (-1.20, -0.17) | 0.01 | 82.8 | < 0.001 |
Type of diabetes | |||||
T2DM | 23 | -0.16 (-0.30, -0.02) | 0.02 | 78.7 | < 0.001 |
T1DM | 9 | -0.76 (-1.37, -0.15) | 0.01 | 80.8 | < 0.001 |
Diabetic nephropathy | 2 | -0.24 (-0.56, 0.07) | 0.12 | 0 | 0.90 |
T2DM & T1DM | 1 | 0.00 (-0.34, 0.34) | 1.00 | 0 | - |
Diabetic neuropathy | 1 | -0.18 (-0.66, 0.30) | 0.45 | 0 | - |
Risk of bias e | |||||
High | 30 | -0.28 (-0.42, -0.13) | < 0.001 | 79.4 | < 0.001 |
Low | 6 | 0.01 (-0.17, 0.18) | 0.95 | 25.3 | 0.24 |
Vitamin E intake on fasting Insulin concentrations | |||||
Overall | 18 | -1.05 (-1.53, -0.58) | < 0.001 | 52.7 | 0.005 |
Intervention duration (week) | |||||
< 10 | 8 | -0.88 (-1.27, -0.49) | < 0.001 | 0.0 | 0.80 |
≥ 10 | 10 | -1.06 (-1.86, -0.26) | 0.009 | 57.8 | 0.01 |
Type of vitamin E | |||||
α-tocopherol | 12 | -0.87 (-1.60, -0.14) | 0.01 | 53.5 | 0.01 |
Tocoterienol | 1 | -0.88 (-1.33, -0.43) | < 0.001 | 100 | - |
Mixed-tocopherols | 1 | -1.40 (-5.94, 3.14) | 0.54 | 100 | - |
Unclear | 4 | -1.54 (-2.79, -0.29) | 0.01 | 23.1 | 0.27 |
Dosage of Vitamin E (mg/day) | |||||
< 500 | 9 | -1.06 (-1.73, -0.39) | 0.002 | 15.1 | 0.30 |
≥ 500 | 9 | -1.00 (-1.68, -0.32) | 0.004 | 66.1 | 0.003 |
Study location | |||||
Western countries | 6 | -1.28 (-1.92, -0.64) | < 0.001 | 61.1 | 0.02 |
Non-Western countries | 12 | -0.87 (-1.56, -0.19) | 0.01 | 35.3 | 0.10 |
Study design | |||||
Blinded | 16 | -1.02 (-1.53, -0.52) | < 0.001 | 56.6 | 0.003 |
Non-blinded | 2 | -0.18 (-6.53, 6.18) | 0.05 | 28.1 | 0.23 |
Type of diabetes | |||||
T2DM | 17 | -1.03 (-1.55, -0.51) | < 0.001 | 55.1 | 0.003 |
Diabetic nephropathy | 1 | -1.20 (-2.31, -0.09) | 0.03 | 0 | - |
Risk of bias e | |||||
High | 12 | -1.05 (-1.85, -0.24) | 0.011 | 44.6 | 0.047 |
Low | 6 | -0.89 (-1.27, -0.51) | < 0.001 | 0 | 0.46 |
Vitamin E intake on HOMA-IR | |||||
Overall | 12 | -0.44 (-0.82, -0.05) | 0.02 | 83.4 | < 0.001 |
Intervention duration (week) | |||||
< 10 | 4 | -0.18 (-0.43, 0.07) | 0.15 | 6.5 | 0.36 |
≥ 10 | 8 | -0.73 (-1.36, -0.08) | 0.02 | 87.6 | < 0.001 |
Type of vitamin E | |||||
α-tocopherol | 8 | -0.72 (-1.29, -0.15) | 0.01 | 87.5 | < 0.001 |
Tocoterienol | 1 | -0.10 (-0.39, 0.19) | 0.49 | 0 | - |
Unclear | 3 | 0.0 (-0.57, 0.58) | 0.98 | 0 | 0.67 |
Dosage of Vitamin E (mg/day) | |||||
< 500 | 7 | -0.98 (-1.83, -0.13) | 0.02 | 88.7 | < 0.001 |
≥ 500 | 5 | -0.17 (-0.55, 0.20) | 0.36 | 69.5 | 0.01 |
Study location | |||||
Western countries | 2 | -0.33 (-0.74, 0.08) | 0.11 | 86.0 | 0.007 |
Non-Western countries | 10 | -0.59 (-1.26, 0.08) | 0.08 | 84.6 | < 0.001 |
Type of diabetes | |||||
T2DM | 11 | -0.47 (-0.88, -0.05) | 0.02 | 84.8 | < 0.001 |
Diabetic nephropathy | 1 | -0.20 (-1.03, 0.63) | 0.63 | 0 | - |
Risk of bias e | |||||
High | 7 | -0.95 (-1.93, 0.02) | 0.054 | 88.8 | < 0.001 |
Low | 5 | -0.18 (-0.38, 0.02) | 0.084 | 0 | 0.518 |