Objectives: The association between coffee consumption, type 2 diabetes and impaired glucose tolerance was examined. In addition, indicators of insulin sensitivity and beta-cell function according to homeostasis model assessment were studied in relation to coffee consumption.
Design: Population-based cross-sectional study.
Setting and subjects: The study comprised 7949 healthy Swedish subjects aged 35-56 years residing within five municipalities of Stockholm. An oral glucose tolerance test identified 55 men and 52 women with previously undiagnosed type 2 diabetes and 172 men and 167 women with impaired glucose tolerance. Information about coffee consumption and other factors was obtained by questionnaire.
Results: The relative risks (adjusted for potential confounders) of type 2 diabetes and impaired glucose tolerance when drinking >/=5 cups of coffee per day compared with </=2 cups per day in men were 0.45 [95% confidence intervals (CI) 0.22-0.92] and 0.63 (CI: 0.41-0.97), respectively, and in women 0.27 (CI: 0.11-0.66) and 0.47 (CI: 0.29-0.76) respectively. In subjects with type 2 diabetes and impaired glucose tolerance, high coffee consumption (>/=5 cups day(-1)) was inversely associated with insulin resistance. In addition, in those with type 2 diabetes and in women (not in men) with impaired glucose tolerance high coffee consumption was inversely associated with low beta-cell function. In women, but not obviously in men, with normal glucose tolerance, coffee consumption was associated with a reduced risk of insulin resistance.
Conclusions: The results of this study indicated that high consumers of coffee have a reduced risk of type 2 diabetes and impaired glucose tolerance. The beneficial effects may involve both improved insulin sensitivity and enhanced insulin response.