MONDAY, Sept. 12, 2005 (HealthDay News) -- Men who down seven or more drinks a day have a significantly increased risk of atrial fibrillation, the irregular heartbeat that can lead to stroke, a study finds.
Men who had 35 or more drinks a week were up to 63 percent more likely to develop atrial fibrillation than those who had less than one drink a week, according to a report in the Sept. 13 issue of Circulation. The study tracked the drinking habits and health of more than 16,000 residents of Copenhagen, Denmark, for 18 years.
Atrial fibrillation can cause blood clots to form in the heart. They can travel to the brain and block an artery there, resulting in a stroke. From 15 percent to 20 percent of strokes are due to atrial fibrillation, said lead researcher Dr. Kenneth J. Mukamal, an internist at Beth Israel Deaconness Medical Center in Boston.
The crucial point of the study was that the risk of atrial fibrillation was largely confined to the heaviest drinkers, Mukamal said. "There was a very dramatic gradient where risk seems to be low among people who don't drink or drink moderately, but when men got to five drinks a day there was a substantial increase in risk."
In the study, the low level of risk was the same for people who never drank and those who had up to 14 drinks a week. There was only a slight increase in risk for men who had up to 34 drinks a week, with the 45 percent increase in risk seen only in men who had 35 or more drinks a week. That risk rose to 63 percent after researchers adjusted for other conditions such as high blood pressure, coronary heart disease and heart failure.
Women reported a lower level of alcohol consumption, with only 3.5 percent of them saying they had more than 21 drinks a week. No increased incidence of atrial fibrillation was found in those women, but it would be safe to assume that heavy drinking increases the risk of atrial fibrillation in both sexes, Mukamal said.
"We looked at a variety of features that might differentiate the people in the study," he said. "We looked at older men vs. younger men, heavier men versus leaner men, and basically we saw similar findings in all of them. I think that means the results broadly apply to all adults."
There is some evidence that light drinking may even have a protective effect in warding off stroke, said Dr. Ralph Sacco, a professor of neurology at Columbia University. "In the AHA guidelines, we have stated that small amounts of alcohol, up to two drinks a day, reduce the risk of stroke."
The current recommendation for stroke prevention is "no more than two drinks a day for men and one a day for non-pregnant women," Sacco said. Pregnant women are advised to abstain completely, to protect the developing fetus.
While Sacco said his expertise is confined to stroke, the heart association guidelines "are also helpful for heart disease," he said. The same rule -- two drinks a day for men, one a day for non-pregnant women -- apply to heart disease, Sacco said.
Another study in the same issue of the journal concerned the use of warfarin, a clot- preventing drug, to reduce the risk of dangerous blood clots in people with atrial fibrillation.
Researchers at the University of California in San Francisco reported that their study of more than 13,000 adults with atrial fibrillation found that women were more likely than men to form such blood clots, but that taking warfarin reduces the risk for both sexes.
Some doctors have been reluctant to prescribe warfarin for women for fear of excess bleeding, but the study shows that the benefit greatly outweighs the risk, the researchers said.
Find out more about drinking and the heart at the American Heart Association.