Research on more than 4,000 people in Costa Rica found that about half had the trait and were considered "slow caffeine metabolizers." The other half had the opposite trait, which caused their bodies to rapidly break down or metabolize caffeine, and coffee-drinking in this group appeared to reduce heart attack risks.
Among slow-metabolizers, those who drank two or more cups of coffee daily were at least 36 percent more likely to have a nonfatal heart attack than those who drank little or no coffee. Even higher risks were found for younger slow metabolizers - those under 50. They were up to four times more likely to have a heart attack than slow metabolizers in their age group who drank little or no coffee. . . .
Still, even if future research confirms the findings, it's likely that caffeine plays a much smaller role in heart attacks than conventional risk factors like high blood pressure, cholesterol and smoking, . . . The study "doesn't say you can't have caffeine," but drinking several cups of coffee daily is probably excessive for some people[.]