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