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% 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.
Listen to your body
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% of skiers who completed the race at least
five times during the decade developed an irregular rhythm, compared to about
1.4% of those who completed one race.
What's more, those who finished the race in the shortest amount of time were
about 30% 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
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 said.
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 said. It's still unknown, he said,
whether athletes have more or fewer arrhythmias than those in the general
"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.