Salazar-Martinez E, Willet WC, Ascherio A, et al: Coffee consumption and risk for type 2 diabetes mellitus. Ann Intern Med 2004;140(1):1-8.
In the short term, caffeine reduces insulin sensitivity and impairs glucose tolerance, but it also increases energy expenditure and contains potassium, niacin, magnesium, and antioxidant substances that may have beneficial effects on the development of diabetes. This study followed 41,394 men and 84,276 women for 12 to 18 years in the Health Professionals' and Nurses' Health studies. In both groups, higher coffee consumption was strongly associated with reduced risk for type 2 diabetes even after adjustments were made for age, body mass index, and other risk factors.
The multivariate relative risks for diabetes according to regular coffee consumption groups (0, <1, 1 to 3, 4 to 5, or >=6 cups per day) in men were 1.0, 0.98, 0.93, 0.71, and 0.46 respectively (P = 0.007 for trend). The corresponding relative risks in women were 1.0, 1.16, 0.99, 0.7, and 0.71 respectively (P <0.001 for trend). Persons who drank 4 cups or more daily of decaffeinated coffee also had a lower relative risk of developing diabetes (0.74 for men and 0.85 for women) compared with nondrinkers. These data suggest that long-term coffee consumption is associated with a statistically significant lower risk for type 2 diabetes, although the data do not prove a cause and effect relationship. It is premature to advise increased coffee drinking as a means to prevent diabetes.