New research suggests that as the frequency of vigorous exercise increases, so does the risk of atrial fibrillation.

Although vigorous exercise has numerous health benefits, case reports and limited data suggest that elite athletic men engaging in endurance exercise...may be at higher risk for the development of atrial fibrillation, Dr. Anthony Aizer, from New York University Medical Center, and colleagues note in the American Journal of Cardiology.

Atrial fibrillation is a heart rhythm disorder, usually involving a rapid heart rate, in which the upper heart chambers (atria) contract in a disorganized and abnormal manner. This can cause an inefficient amount of blood to be pumped through the heart. Although the condition is usually well-controlled with treatment, atrial fibrillation can lead to fainting, heart failure and stroke.

To explore this topic further, the researchers analyzed data from 16,921 apparently healthy men who participated in the Physicians' Health Study, a prospective investigation started in 1982. During follow-up, 1661 men reported that they developed atrial fibrillation, according to the report.

The participants answered questionnaires that included questions on vigorous exercise, which was defined as exercise that makes the exerciser break a sweat. The analysis showed that compared with participants who participated in no vigorous exercise, vigorous exercise 5 to 7 days per week increased the odds of atrial fibrillation by 20 percent.

Upon further analysis of the subgroup of vigorous exercisers, the association was only apparent in men younger than 50 years of age and in joggers. Comparing 5 to 7 days of vigorous exercise with no vigorous exercise, the risk of atrial fibrillation was elevated by 74 percent among younger men and by 53 percent among joggers.

As with any observational study, this study does not prove that vigorous exercise is a direct cause of atrial fibrillation; plus it is possible that unknown confounding factors were not considered, the authors conclude. However, vigorous exercise was directly associated with several atrial fibrillation risk factors, and, therefore, it is also possible that more complete control for risk factors would have strengthened the... associations observed.

SOURCE: American Journal of Cardiology, June 1, 2009.