The latest finding may be the reason why past studies have conflicting results that coffee may be bad for your heart. The underlying factor is a genetic link in some people that may cause over 2 cups per day to increase their risk of a heart attack. Here is one of several articles that hit the news wires today based on a report in the Journal of the American Medical Association.

Here’s a real caffeine jolt—heart attacks might be a risk for coffee drinkers with a common genetic trait that makes caffeine linger in their bodies, a study suggests.

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.