Review
Annual incidence and relative risk of diabetes in people with various categories of dysglycemia: A systematic overview and meta-analysis of prospective studies

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Abstract

Background

Several estimates of the risk of progression to diabetes in people with impaired fasting glucose (IFG) or impaired glucose tolerance (IGT) have been reported.

Objective

To provide an estimate of the risk of progression to diabetes and regression to normoglycemia in these populations.

Design

Systematic overview and meta-analysis of prospective cohort studies published from 1979 until 2004.

Setting

Global cohort studies.

Patients

People with IFG or IGT detected by a screening oral glucose tolerance test.

Measurements

Fasting and post-load plasma glucose levels.

Results

The absolute annual incidence of diabetes in individuals with various categories of IFG or IGT varied from 5 to 10%. Compared to normoglycemic people the meta-analyzed relative risk and 95% confidence interval for diabetes was: 6.35 (4.87–7.82) in people with IGT; 5.52 (3.13–7.91) in people with isolated IGT; 4.66 (2.47–6.85) in people with IFG; 7.54 (4.63–10.45) in people with isolated IFG; and 12.13 (4.27–20.00) in people with both IFG and IGT. People with IGT were 0.33 times as likely to be normoglycemic after 1 year compared to people with normal glucose tolerance (95% CI 0.23–0.43).

Limitations

Studies that used differing criteria for IFG and IGT were included, and participants were classified on the basis of only one test.

Conclusion

IFG and IGT are associated with similar, high relative risk for incident diabetes. The combined abnormality of IFG plus IGT is associated with the highest relative risk.

Introduction

Diabetes is a common chronic disease that is rapidly increasing in prevalence and that now affects more than 5% of the global adult population [1]. It is diagnosed when fasting plasma glucose levels are persistently ≥7 mmol/l and/or when 2 h glucose levels following a 75 g oral glucose load are persistently ≥11.1 mmol/l. People whose glucose levels are elevated but are still below these thresholds are at higher risk for progressing to diabetes than people with normal values [2]. They are typically classified as having impaired fasting glucose (i.e. IFG—a fasting plasma glucose ≥6.1 mmol/l and <7 mmol/l in the absence of diabetes) and/or impaired glucose tolerance (i.e. IGT—a 2 h plasma glucose ≥7.8 mmol/l and <11.1 mmol/l)—dysglycemic categories that currently affect approximately 8% of adults worldwide (Table 1) [1].

Several epidemiologic studies have reported estimates of the absolute and relative risks of progression to diabetes in people with IFG or IGT. These studies were conducted in a variety of different populations, measured diabetes in different ways, used different statistics to report the results, and reported different estimates of risk. They also did not consistently report the likelihood of regression to normoglycemia.

This systematic review and meta-analysis therefore summarizes the current literature and provide an estimate of the risk of progression to diabetes and regression to normoglycemia in people with IFG or IGT. It is particularly relevant in light of the growing diabetes epidemic, and emerging evidence that diet, lifestyle and a growing list of pharmacologic interventions can reduce the incidence of diabetes in these people.

Section snippets

Methods

Primary articles that were published in English from 1979 until February 2004 that reported data from prospectively followed cohorts of individuals with IFG or IGT were sought from either epidemiologic cohort studies or the control group of randomized controlled trials. Studies were included for analysis if they: (a) prospectively followed ambulatory participants for at least 1 year within an epidemiologic study or randomized trial; (b) reported data from people with IFG, IGT or both metabolic

Retrieved studies

A total of 25,521 citations were identified and screened [8]. Review of the titles and abstracts of these citations yielded 1243 articles for full-text screening. Of the articles that met the inclusion and exclusion criteria; 35 articles reported data from 21 cohort studies [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41] and 9 reported data from

Discussion

This meta-analysis of carefully selected prospective cohort studies found that every category of dysglycemia was associated with a high relative risk for future diabetes. Thus individuals with IGT, IFG, IIGT, IIFG, and both IGT and IFG had annualized relative risks that ranged from 4.7 to 12 with absolute annual risks generally varying from 5 to 10%. Comparisons within the same study that spanned the dysglycemic classification groups were limited to three studies [31], [37], [38]. Nevertheless

Acknowledgments

This systematic review more fully describes findings listed in the report prepared for the Agency for Healthcare Research and Quality (contract no. 290-02-0020) Evidence Report (Publication No. 05-E026-2).

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    Dr. Gerstein holds the McMaster University Population Health Institute Chair in Diabetes Research (sponsored by Aventis) and Dr. Raina holds Canadian Institute of Health Research Investigator award and a holder of Ontario Premier's Research Excellence award. This systematic review was funded by the Agency for Healthcare Research and Quality, United States Department of Health and Human Services (contract no. 290-02-0020). The authors are solely responsible for the content of the review. The opinions expressed herein do not necessarily reflect the opinions of the Agency for Healthcare Research and Quality.

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