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 as likely to have a heart attack than slow metabolizers in their age group who drank little or no coffee.
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The findings, though preliminary, might explain why there have been such mixed results in previous studies investigating caffeine's effects on the cardiovascular system, said University of Toronto researcher Ahmed El-Sohemy, a study co-author.
Caffeine is thought to block the effects of a certain chemical that is believed to help protect against tissue damage, he said.
Some previous research has linked coffee-drinking to a higher risk of heart disease, but other studies have suggested the opposite. While there's evidence to suggest caffeine can cause short-term blood-pressure increases, a study last year said coffee-drinking didn't appear to cause long-term high blood pressure, at least in women.
There's no easy way to know if you're a fast or slow caffeine metabolizer. Staying awake all night if you drink coffee in the afternoon doesn't mean you're a slow metabolizer, and a genetic test that could answer the question is used in research but is not commercially available, El-Sohemy said.
His study, conducted with researchers from Harvard's School of Public Health and the University of Costa Rica, appears in today's Journal of the American Medical Association.
