People with heart disease who drink, even moderately, may have a slightly increased risk of a common heart rhythm problem, new Canadian research suggests.

The study is not the first to link moderate drinking to the heart arrhythmia, known as atrial fibrillation (AF). But it is still not clear that the habit itself is the problem.

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.

Things get murky, though, when it comes to moderate drinking, the report in the Canadian Medical Association Journal says.

In general, it is thought that having one or two drinks a day is protective against coronary heart disease – where cholesterol-containing “plaque” builds up in the arteries.

But modest drinking has not been linked to a decreased risk of AF and the new findings suggest that when people already have heart issues moderate drinking is actually tied to more AF cases.

The study included more than 30,000 older adults who either had clogged arteries, a history of stroke or diabetes complications such as kidney disease. Most had coronary heart disease.

Over about five years, people who drank occasionally or not at all developed AF at a rate of about 1.5% each year. For moderate drinkers, the rate was 1.7%, and for heavy drinkers it was 2.1%.

The researchers looked at other factors, too – like age, weight and smoking habits. But moderate drinking was still linked to a 14% increase in the risk of AF.