Drinking even a small amount of alcohol may increase a person’s risk of atrial fibrillation, according to a new study.

After adjusting for multiple variables, researchers found that every 10 grams of alcohol consumed per day was associated with a 5 percent higher risk of developing new-onset atrial fibrillation. Ten grams of alcohol is just under one drink. They added that left atrial enlargement explained an estimated 24 percent of the association between alcohol and atrial fibrillation risk.

Lead researcher David D. McManus, MD, of the University of Massachusetts Medical School, and colleagues published their results online in the Journal of the American Heart Association Sept. 14.

“Our study provides the first human evidence of why daily, long-term alcohol consumption may lead to the development of this very common heart rhythm disturbance,” Gregory Marcus, MD, a senior study author, said in a news release. “We were somewhat surprised that a relatively small amount of alcohol was associated with a larger left atrium and subsequent atrial fibrillation.”

They analyzed 5,220 participants from the original and offspring cohorts of the Framingham Heart Study who were evaluated by a physician approximately every four to eight years. Physicians conducted a physical examination, gave participants a 12-lead electrocardiogram and obtained a thorough medical history at every visit. They also asked participants about their alcohol consumption via three questions asked as part of the medical history.

The mean age of participants was 56.3 years old, and more than half were women. Most of the participants did not have cardiovascular disease at baseline. The mean alcohol consumption was 13.3 grams per day, while the mean left atrial dimension (LAD) at baseline was 38.3 mm.

After a median of six years of follow-up, the incidence of atrial fibrillation was 8.4 per 1,000 person years. Alcohol intake and LAD at baseline were similar between the original and offspring cohorts, according to the researchers.

When the researchers adjusted for multiple variables, they found that every additional 10 grams of alcohol consumed per day was associated with a 0.16 mm higher LAD. They added that there was no significant association between alcohol and the change in LAD and that alcohol consumption was not associated with change in left atrial size for men or women.

“Our data suggest atrial fibrillation might be prevented by avoiding alcohol—however, just as alcohol likely has variable effects on individuals, there are almost certainly various mechanistic subtypes of atrial fibrillation,” Marcus said. “It’s not one size fits all when it comes to the effects of alcohol and heart health. … Our hope is that by understanding the mechanistic relationship between alcohol and atrial fibrillation we might learn something inherent to atrial fibrillation in general that could help identify new ways of understanding and treating the disease.”

The researchers mentioned a few limitations of the study, including that atrial fibrillation may be asymptomatic and not clinically detected and that the method they used may not have reflected the participants’ true atrial size. They also noted that most of the participants were middle-aged to older adults and white, so the results may not be generalizable to other age or racial groups.

“These data, although observational, are consistent with the notion that chronic alcohol consumption, even at moderate levels, can be cardiotoxic and lead to pathological atrial structural change that can, in turn, enhance vulnerability to [atrial fibrillation] later in life,” the researchers wrote.