Marathon runners who travel by air to the race may end up with higher blood levels of thrombotic risk markers, a new study shows.
That doesn't mean flying is likely to trigger a blood clot in endurance athletes, researchers say, or that air travel is a no-go. But it does suggest a possible explanation for the rare but mysterious reports of clots in otherwise healthy marathoners who flew to a race.
"It seems that the two activities could have a compounding effect when they are carried out back-to-back," said Dr Beth A. Parker at Hartford Hospital in Connecticut, who led the research.
In the new study, published online in the American Journal of Cardiology, Dr Parker and her colleagues took venous blood samples from 41 healthy non-smokers who ran in the 2010 Boston Marathon.
Old athletes have high inflammatory levels
Twenty-three of them lived more than a four-hour plane flight away; while 18 – the control group – lived within a two-hour drive of Boston. The researchers collected blood after the runners landed in Boston, immediately after the marathon, and again when the participants were back home the next day.
"Six travel subjects versus zero controls had d-dimer values >500 ng/mL after returning home the day after the marathon, the clinical threshold for excluding venous thrombosis (p=0.03)," the researchers wrote.
None of the athletes showed actual symptoms of deep vein thrombosis.
The researchers also found that older athletes had significantly higher levels of the inflammatory marker p-selectin (p = 0.01), a cell adhesion molecule that could be associated with heart attack risk, regardless of whether they flew to the marathon or not.
No need to worry for runners
One expert who wasn't part of the study cautioned that none of the molecules the researchers looked at has been shown to clearly identify individuals at increased risk of clots or heart disease.
"I wouldn't let these findings alarm runners travelling to marathons," Dr Kenneth Bauer of Beth Israel Deaconess Medical Centre in Boston said.
Dr Parker agrees that while the research suggests marathons and air travel to get to them could contribute to a slightly increased risk of blood clots or other cardiovascular events, the benefits of endurance running far outweigh the small risks for most people.
One of the researchers on Dr Parker's team consults for AstraZeneca, which makes the cholesterol-lowering drug Crestor, and a number of other major pharmaceutical companies that make heart drugs.
(Lindsey Konkel, Reuters Health, March 2012)