In this prospective study in diabetic men, higher habitual coffee consumption was not associated with a higher risk of CVD or all-cause mortality. We did not find significant associations for decaffeinated coffee or total caffeine intake either.
Coffee is a major source of caffeine. Several studies showed that caffeine acutely impaired postprandial glucose metabolism in diabetic patients (8
). In addition, concerns have been raised in short-term trials that caffeine increases blood pressure (10
) and homocysteine levels (11
). However, findings from short-term caffeine intervention studies cannot be extrapolated to the effects of chronic coffee consumption on risk of CVD. First, physiological effects of coffee can be different from those of caffeine. It has been shown that caffeine results in a larger increase in epinephrine concentrations than intake of the same amount of caffeine in coffee (12
). Moreover, coffee contains various substances such as antioxidants (i.e., chlorogenic acid) that may improve glucose metabolism and insulin sensitivity (13
). Second, the acute effects of caffeine could be transient because partial tolerance to the humoral and hemodynamic effects of caffeine among habitual drinkers might develop after several days of use (14
In this study, the availability of updated measures of coffee and covariates during the follow-up enabled us to incorporate changes in coffee consumption into the analysis. Because coffee drinking is often thought to be an unhealthy habit, people may quit or reduce the consumption of coffee to improve their health after developing hypertension or hypercholesterolemia. These changes would dilute a possible positive association between coffee and CHD or stroke. To reduce this bias, we excluded subjects with hypertension or hypercholesterolemia at baseline. We also conducted a sensitivity analysis where we used short-term caffeinated coffee consumption in relation to CVD and mortality, which yielded very similar results. As illustrated by the upper limits of 95% CIs of our RR estimates, we cannot exclude the possibility that we missed an association between coffee consumption and a modestly higher risk of CVD due to chance. However, results from a previous study in Finnish individuals with diabetes support the lack of a direct association and even suggest an inverse association between coffee and CVD mortality (5
In conclusion, in this large prospective study of U.S. men, our findings do not support the hypothesis that habitual caffeinated coffee consumption increases risk of cardiovascular events or mortality among individuals with type 2 diabetes.