[Coffee and cardiovascular disease risk: yin and yang]

Many epidemiological studies have addressed the effects of coffee on cardiovascular disease. Most case-control studies suggest an increased risk in high coffee consumers, whereas cohort studies indicate no clear association with cardiovascular risk. Several aspects could be considered to explain and/or reconcile these inconsistencies. Selection bias and recall bias may explain a positive association supported by case-control studies. An inadequate adjustment for many confounding factors (i.e., smoking, poor diet, sedentary lifestyle, etc.) could also affect the relationship between coffee consumption and cardiovascular risk. Moreover, coffee contains several biologically active substances that may have either beneficial or harmful effects on the cardiovascular system. The development of complete/partial tolerance to some caffeine effects in habitual drinkers adds to the complexity of coffee effects. Variation in cup size and methods of coffee preparation may also explain some conflicting results. As it is not reasonable to conduct randomized controlled trials, it is recommended that coffee consumption be moderate in healthy people and limited in individuals at high risk.