Chicago, Illinois (AHN)-A new study suggests heart attacks might be a risk for coffee drinkers with a common genetic trait that makes caffeine linger in their bodies.

According to the Associated Press, research on more than 4,000 people in Costa Rica found that about half had the trait and were considered "slow caffeine metabolizers." Conversely, 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.

University of Toronto researcher and study co-author, Ahmed El-Sohemy, says the findings, though preliminary, might explain why there have been such mixed results in previous studies investigating caffeine's effects on the cardiovascular system.

While some previous research has linked coffee-drinking to a higher risk of heart disease, other studies have suggested the opposite. While there's evidence to suggest caffeine can cause short-term blood pressure increases, a study last year revealed coffee-drinking didn't appear to cause long-term high blood pressure, at least in women.

El-Sohemy says the new study "clearly illustrates that one size does not fit all...Perhaps in the future we'll be making different (dietary) recommendations based on people's genetic makeup."

The study, conducted with researchers from Harvard's School of Public Health and the University of Costa Rica, appears in Wednesday's Journal of the American Medical Association.