RESULTS: After adjustment for potential confounders, the relativerisk of type 2 diabetes was 0.87 (95% CI 0.73-1.03) for one cup per day, 0.58 (0.49-0.68) for two to three cups per day, and 0.53 (0.41-0.68) for four or more cups per day compared with nondrinkers (P for trend <0.0001). Associations were similar for caffeinated (0.87 [0.83-0.91] for a one-cup increment per day) and decaffeinated (0.81 [0.73-0.90]) coffee and for filtered (0.86 [0.82-0.90]) and instant (0.83 [0.74-0.93]) coffee. Tea consumption was not substantially associated with risk of type 2 diabetes (0.88 [0.64-1.23] for four or more versus no cups per day; P for trend = 0.81).
CONCLUSIONS: These results suggest that moderate consumption of both caffeinated and decaffeinated coffeemay lowerrisk of type 2 diabetes in younger and middle-agewomen. Coffee constituents other than caffeine may affect the development of type 2 diabetes.