Atrial fibrillation, which can be brought on by heavy drinking, results in a fivefold increase in the chance of having a stroke.

Drinking 52 units of alcohol or more a week increased the risk of a type of arrhythmia that is a major cause of strokes by up to 45 percent among men, according to research to be published today.

The scientists behind the work said their research supported the idea of "holiday heart syndrome," named because doctors noticed a high number of patients were reporting heart problems after returning from a break.

Hazardous Rhythm

The researchers, from Beth Israel Deaconess Medical Center in Boston in the United States, looked at test results from more than 16,000 people who took part in a health study in Copenhagen.

The lead author of a report published today in the journal Circulation, Professor Kenneth Mukamal, said they found little difference in the risk of developing an irregular heartbeat between teetotallers and people consuming up to 21 units a week.

"But among men who typically drank 35 or more alcoholic beverages (equivalent to 52.5 units) per week, the risk of atrial fibrillation increased significantly, by 45 percent," he said.

"This was certainly the largest study of its type to examine this topic. And while it is reassuring that moderate drinkers did not seem to have an increased risk of this hazardous heart rhythm, our findings provide yet more evidence of the risks of heavy drinking to the heart."

Blood Clots Form

A pint of beer has two units of alcohol while a glass of wine, sherry or a spirit has one. There were too few women classed as "heavy drinkers" in the sample to come to a conclusion about them.

This type of arrhythmia, atrial fibrillation, develops when muscles in the heart's upper chambers contract too quickly, resulting in an irregular heartbeat. Blood is then not adequately pumped from the heart, and may pool and form clots. Blood clots that travel to the brain result in a stroke.

Statistics show that having atrial fibrillation results in a fivefold increase in the chance of having a stroke.

Scientists studied information from the Copenhagen City Heart Study in Denmark covering 16,415 people with an average age of 50. There were 1,071 cases of atrial fibrillation during the study period.

Heart Failure

Dr. Andrew Rankin, a consultant cardiologist at Glasgow University, said the health of a patient was a crucial factor in determining how dangerous atrial fibrillation was.

He said: "One of the major concerns about it (atrial fibrillation) is it is associated with the risk of having a stroke. It depends on who your patient is. If they have a structurally normal heart, then their risk of having problems like a stroke is actually quite low."

Dr. Rankin added: "Small clots can form [in the heart] and if they shoot off you can have a stroke, but it's not like a ventricular fibrillation, when you drop down dead.

"However, it can drive the heart faster, that can put a strain on it and you can have heart failure."

He said the research reinforced advice on alcohol: "All things in moderation -- that's always the general message."