Smith B et al. (2006) Does coffee consumption reduce the risk of type 2 diabetes in individuals with impaired glucose? Diabetes Care 29: 2385–2390

Coffee consumption has been suggested to reduce the risk of developing type 2 diabetes. Previous studies, however, mostly relied on self-reported diabetes. Smith and colleagues examined a white Californian community to assess the association between coffee drinking and incident diabetes—defined as no history of diabetes at baseline with subsequent onset of diabetes confirmed by oral glucose tolerance tests.

In total, 910 adults (mean age 65.9 years) were followed for 8 years on average after assessment of coffee intake. Data from 593 participants with normal baseline glucose levels and 317 participants with impaired baseline glucose levels were analyzed separately. Of the 910 participants, 97 never drank coffee, 153 were past coffee drinkers and 660 were current coffee drinkers (who consumed 2.8 cups per day on average). The risk of type 2 diabetes was approximately 60% lower in current and past coffee drinkers (odds ratios 0.36 and 0.38, 95% CI 0.19–0.68 and 0.17–0.87, respectively) than in individuals who never drank coffee. This effect was similar in participants with normal or impaired baseline glucose levels and was independent of age, sex, exercise, BMI, smoking, alcohol consumption and hypertension.

The authors discuss the possible physiological mechanisms of the protective effect of coffee and the geographical differences in terms of the contents of the coffee consumed. The component of coffee responsible for its favorable effect on the risk of diabetes, however, remains to be investigated.