People who drink regularly, especially heavy drinkers, may be more likely than teetotalers to suffer the common heart-rhythm disturbance atrial fibrillation, a new research review suggests.
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 per cent more likely to suffer atrial fibrillation, or AF, than either non-drinkers or occasional drinkers.
Doctors have long known that a drinking binge can trigger an episode of AF, in which the heart's upper chambers begin to quiver chaotically instead of contracting normally.
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 Reuters Health in an e-mail.
But the study, reported in the Journal of the American College of Cardiology, also found evidence linking fairly moderate drinking to a higher AF risk, compared with abstinence.
Overall, the risk of AF crept up eight per cent for every increase of 10 grams (about a third of an ounce) in study participants' daily alcohol intake.
That might sound surprising, Sone said, since moderate drinking - up to one or two drinks per day - is thought to be protective against coronary heart disease, in which plaque builds up in the arteries.
But moderate drinking has never been linked to a decreased risk of AF.
Atrial fibrillation arises from a problem in the heart muscle's electrical activity. Unlike ventricular fibrillation, which affects the heart's lower pumping chamber, AF is not immediately life-threatening. In some cases, an AF episode is short-lived and goes away on its own - in what's called paroxysmal AF.
But in some people, AF becomes recurrent or permanent, raising their risk of heart failure and of blood clots that can travel to the brain and cause a stroke. So lowering the risk of developing AF in the first place is important.
More than 2.6 million Americans will suffer AF this year, according to the US Centers for Disease Control and Prevention. 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, 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.
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," Mukamal said in an e-mail.
He expressed doubts, however, that moderate drinking would increase the risk of AF.
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.
Mukamal also pointed out that of the studies in the current analysis, it was the so-called "case-control" studies that showed the strongest link between drinking and AF. Those kinds of studies - which compare AF patients with healthy individuals - 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, Mukamal said, "there's little risk from chronic drinking in moderation, but heavier drinking - even rarely - acutely increases risk."
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