Objective: This meta-analysis was undertaken to obtain insight regarding the shape and strength of the relationship between alcohol consumption and the risk of type 2 diabetes, the effects of adjustment for confounders, and the effect of modification by type 2 diabetes definition, sex, and BMI.
Research design and methods: The 15 original prospective cohort studies that were included comprise 11,959 incident cases of type 2 diabetes in 369,862 individuals who, on average, were followed for 12 years.
Results: After pooling the data, a U-shaped relationship was found. Compared with nonconsumers, the relative risk (RR) for type 2 diabetes in those who consumed </=6 g/day alcohol was 0.87 (95% CI 0.79-0.95). For the moderate consumption ranges of 6-12, 12-24, and 24-48 g/day, RRs of 0.70 (0.61-0.79), 0.69 (0.58-0.81), and 0.72 (0.62-0.84) were found, respectively. The risk of type 2 diabetes in heavy drinkers (>/=48 g/day) was equal to that in nonconsumers (1.04 [0.84-1.29]). In general, nonsignificant trends for larger RR reduction associated with moderate alcohol consumption were observed for women compared with men, for crude compared with multivariate-adjusted analyses, and for studies that used self-reports instead of testing for type 2 diabetes definition. No differences in RR reductions were found between individuals with low or high BMI.
Conclusions: The present evidence from observational studies suggests an approximately 30% reduced risk of type 2 diabetes in moderate alcohol consumers, whereas no risk reduction is observed in consumers of >/=48 g/day.