Coffee drinkers get a jolt in study

By Denise Gellene and Jia-Rui Chong

The findings of a new medical study may be enough to make you spit out your morning coffee.

And that could be a good thing — at least for half of you.

A study of 4,000 coffee drinkers has found that two or more cups each day can increase the risk of heart disease — but only for those with a genetic mutation that slows the breakdown of caffeine in the body.

In diverse urban areas, the mutation is found in roughly half of all people. People without the mutation can drink as much coffee as they wish with no added risk of a heart attack, scientists said.

Unfortunately for coffee drinkers, there's no commercial test for the mutation, and staying awake all night if you drink coffee during midday doesn't mean you're a slow metabolizer.

"I don't know what to think," Donna Carmichael, 50, said as she waited for a train in Los Angeles. "How do you know if you've got the gene?" she asked, explaining that she usually drinks about three cups of coffee a day. "If it's genetic, though, who's going to go out and get tested?"

The findings, conducted by researchers from the University of Toronto, Harvard's School of Public Health and the University of Costa Rica, are published today in the Journal of the American Medical Association. They could explain why previous investigations into caffeine's effect on the heart have produced conflicting results.