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Critique 182: A major meta-analysis on the association of alcohol consumption with the risk of diabetes mellitus — 8 March 2016

Most previous studies have shown that consumers of light-to-moderate amounts of alcoholic beverages tend to have a significant reduction in their subsequent risk of developing Type II diabetes mellitus (DM). The purpose of the present study was to explore and summarize the evidence on the strength of the association between alcohol consumption and the subsequent risk of DM by using a dose-response meta-analytic approach. The authors identified 26 prospective cohort studies providing data appropriate for a meta-analysis; their analyses were based on 706,716 individuals (275,711 men and 431,005 women) with 31,621 cases of DM.

This meta-analysis reports that light and moderate drinkers have a significantly reduced risk of developing DM. For “light” drinkers (defined as an average of ≤ 12 g/day of alcohol), in comparison with non-drinkers, the overall risk ratio for DM was 0.83, with 95% CIs of 0.73, 0.95 (P = 0.005). For “moderate” drinkers (>12- <24 g/day), the RR was 0.74, with 95% CIs of 0.67, 0.82 (P = 0.001). Thus, data from this meta-analysis indicate a 17% and 26% reduction in the risk of DM, respectively, for these two drinking categories.

For subjects classified as “heavy” users of alcohol (reported intake averaging ≥ 24 g/day), the RR was 0.98, with 95% CIs of 0.83, 1.09, P = 0.480), interpreted as no effect. In a figure in the paper showing the separate results for each individual study included, the point estimates for the risk of DM were 1.0 or less than 1.0 for light and moderate drinkers in essentially all studies. Thus, data from the individual studies support the overall finding of a decrease in risk of DM for light or moderate drinkers.

Sub-group analyses showed that when subjects were stratified by sex, age, BMI, smoking, physical activity, and family history of DM, the point estimates of the risk ratios associated with light or moderate alcohol consumption were less than 1.0 in all groups, adding further to the robustness of the overall conclusions of a reduction in risk of DM from alcohol intake. Similarly, for all subjects, as well as for men and women separately, there was a clear U-shaped curve for the association. The nadir of the effect was just over 20 grams of alcohol per day (about 2 typical drinks), and even the risk of heavy drinkers did not reach the estimated risk of non-drinkers.

Forum members considered this to be a well-done analysis that confirms most previous results from prospective studies indicating a reduction in the risk of developing DM associated with moderate drinking. Further, an increasing number of randomized clinical trials are supporting such beneficial effects on the development and clinical treatment of DM. The Forum thought it unfortunate that beverage-specific results were not available in this study, as increasingly it is being shown that, beyond alcohol effects, there are polyphenols and other substances in wine and beer that provide additional protection against diabetes. Further, the Forum felt it important to also emphasize the protective effects against cardiovascular disease among subjects who already have DM, who are especially vulnerable to coronary heart disease and other effects of atherosclerosis.

Overall, this meta-analysis based on a large number of subjects indicates that the risk of DM is considerable lower among light and moderate drinkers than among abstainers. This finding supports the contention that, for most middle-aged and older adults (with the exception of individuals with specific prohibitions against alcohol such as former drug or alcohol abuse, certain types of neurological or severe hepatic disease, etc.), moderate alcohol consumption should be considered as a component of a “healthy lifestyle” that reduces the risk of diabetes and most of the chronic diseases of ageing.

Reference: Li X-H, Yu F-F, Zhou Y-H, He J. Association between alcohol consumption and the risk of incident type 2 diabetes: a systematic review and dose-response meta-analysis. Pre-publication: Am J Clin Nutr 2016; doi: 10.3945/ajcn.115.114389.

For the full critique of this paper by members of the International Scientific Forum on Alcohol Research, please click here.
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