In an analysis of 14 past studies, researchers found that the heaviest drinkers were more likely to be diagnosed with atrial fibrillation than people who drank little to no alcohol.
The studies differed in how they defined "heavy" drinking. At a minimum it meant two or more drinks per day for men, and one or more per day for women; in some studies, heavy drinkers downed at least six drinks per day.
When all the study results were combined, heavy drinkers were 51% more likely to suffer atrial fibrillation (AF) than either non-drinkers or occasional drinkers.
Doctors have long known that a drinking binge can trigger an episode of AF.
But the new findings suggest that people's habitual drinking habits may also matter, according to the researchers, led by Dr Satoru Kodama of the University of Tsukuba Institute of Clinical Medicine in Ibaraki, Japan.
"What we revealed in the current (study) is that not only episodic but habitual heavy drinking is associated with higher risk of AF," co-researcher Dr Hirohito Sone told.
Moderate drinking linked to a higher AF risk
But the study, reported in the Journal of the American College of Cardiology online 17 January, also found evidence linking fairly moderate drinking to a higher AF risk, compared with abstinence.
Overall, the risk of AF crept up 8% for every increase of 10 grams (about a third of an ounce) in study participants' daily alcohol intake.
That might sound surprising, Dr Sone said, since moderate drinking - up to one or two drinks per day - is thought to be protective against coronary heart disease.
But moderate drinking has never been linked to a decreased risk of AF.
People with AF history should be careful
The condition becomes more common with age and additional risk factors include high blood pressure, diabetes, obesity and hyperthyroidism. The current findings do not mean that cutting out alcohol altogether is a good way to lower one's risk for AF.
Since coronary heart disease is a much more common cause of death than AF, Dr Sone said, moderate drinking is still probably a heart-healthy habit for most people. But, he added, people who have ever had an episode of paroxysmal AF might benefit from not drinking.
Studies are still needed to show whether that is indeed the case, the researcher added.
No protection from AF
It's not surprising that moderate drinking appears to offer no protection from AF, said Dr Kenneth J. Mukamal of Harvard University and Beth Israel Deaconess Medical Center in Boston.
"The ways in which alcohol might prevent coronary heart disease - like better HDL cholesterol and less clotting - are irrelevant for risk of AF," Dr Mukamal said.
He expressed doubts, however, that moderate drinking would increase the risk of AF.
Two studies on AF
Dr Mukamal led two of the studies included in the current analysis. One found a connection only between heavy drinking and AF: men who had five or more drinks per day had a higher risk of developing AF over time than occasional drinkers.
Dr Mukamal also pointed out that of the studies in the current analysis, it was case-control studies that showed the strongest link between drinking and AF, which are not well-designed for showing cause-and-effect.
A better way to show that is with studies that measure people's drinking habits, then follow them over time to see who develops AF.
Based on those types of studies, Dr Mukamal said, "there's little risk from chronic drinking in moderation, but heavier drinking - even rarely - acutely increases risk." (Reuters Health/ January 2011)