NEW YORK (Reuters Health) - Cross-country skiers who have completed more races at faster speeds have a higher risk of developing a heart rhythm disorder than their slower, less-seasoned peers, a new study from Sweden suggests.
Researchers found athletes who completed at least five races over ten years were 30 percent more likely to be diagnosed with an irregular heartbeat, known as an arrhythmia, than those who only finished one race.
"It supports the notion that's been around forever that athletes are not immune to heart disease," said Dr. Aaron Baggish, who studies athletes' heart health but wasn't involved in the new research.
Still, the new findings don't prove athletes' extra exertion caused heart problems.
Previous studies suggested that endurance athletes were at an increased risk of atrial fibrillation (AF), a type of rhythm disorder affecting the heart's upper chambers, but few looked at large numbers of athletes. AF raises the risk of blood clots and stroke.
For the new study, Dr. Kasper Andersen from Uppsala University and his colleagues tracked about 53,000 cross-country skiers who completed the annual 56-mile Vasaloppet race in Sweden between 1989 and 1998.
Overall, 919 of the skiers developed an irregular heartbeat during the study, which ran through 2005.
About 2.7 percent of skiers who completed the race at least five times during the decade developed an irregular rhythm, compared to about 1.4 percent of those who completed one race.
What's more, those who finished the race in the shortest amount of time were about 30 percent more likely to develop an arrhythmia than slower skiers.
The most common type of arrhythmia in the study was AF. But the researchers also found an increased risk of a slow heartbeat, known as bradyarrhythmia, with greater racing experience.
Andersen said he was surprised to see a higher risk of slow heart rhythms among intense athletes, because that had not been reported in past studies.
"It hasn't really been suggested before," he told Reuters Health.
Baggish, associate director of the Cardiovascular Performance Program at the Massachusetts General Hospital Heart Center in Boston, said it's hard to know what to do with the finding about slow heart rhythms.
But he said the study does support what's known about athletes and AF - and there are probably multiple reasons for their extra risk.
The researchers write in the European Heart Journal that training or competing may trigger arrhythmias as the heart adjusts to increased or decreased activity.
But both Baggish and Andersen cautioned that these findings shouldn't keep people from playing sports.
"I think it would be a mistake for people to interpret this as a reason to avoid this type of lifestyle," Baggish told Reuters Health. It's still unknown, he said, whether athletes have more or fewer arrhythmias than those in the general population.
"There are a lot of positive effects of physical activities and exercise, which I think will outweigh the increased risk of rhythm disturbance," Andersen said, adding that athletes should still listen to their bodies.
SOURCE: bit.ly/11vngDg European Heart Journal, online June 12, 2013.