running / Women

Estrogen, Blood Clots and Marathon Running

Picture taken from http://www.runningusa.org/boston-elites-2015?returnTo=mainMarathon running is getting popular! It has increased 40% over the past decade, with 2013 yielding 1100 marathons and 541,000 finishers (57% men, 43% women). I’ve written before in several blog posts about our research at both the Boston Marathon and NU Hartford Marathon. We’ve been pursuing a line of research looking at whether the combination of air travel and marathon running increase the risk of blood clot formation, since there are growing numbers of otherwise healthy athletes who report getting a deep vein thrombosis (DVT) after the combination of travel and running. For example, in the 2010 Boston Marathon, we examined the effect of travel and marathon running on exercise-induced coagulation (clot formation) and fibrinolysis (clot breakdown) markers  in runners who flew across country vs. drove locally to the marathon. We observed that markers of clot formation (but NOT clot breakdown) were greater in runners who flew vs. drove to the marathon. This indicates that the combination of air travel and marathon running may upset the hemostatic balance, or the balance between clot formation and breakdown, such that flying to a marathon increases blood clot risk.  However, since none of the runners in our Boston study actually reported a DVT, we’ve speculated that in most healthy runners, air travel and running alone don’t cause a DVT.

Figure illustrates the hypothetical effect of endurance exercise on the balance between coagulation and fibrinolysis.  In the top figure, a bout of exercise augments activation of both coagulation and fibrinolytic factors such that hemostatic balance is maintained.  In the bottom figure, the superimposition of additional risk factors for DVT in conjunction with a bout of exercise augments coagulatory activation such that the balance between coagulation and fibrinolysis becomes prothrombotic and a DVT occurs.

Figure illustrates the hypothetical effect of endurance exercise on the balance between coagulation and fibrinolysis. In the top figure, a bout of exercise augments activation of both coagulation and fibrinolytic factors such that hemostatic balance is maintained. In the bottom figure, the superimposition of additional risk factors for DVT in conjunction with a bout of exercise augments coagulatory activation such that the balance between coagulation and fibrinolysis becomes prothrombotic and a DVT occurs.

Rather, it’s a “perfect storm” of additional blood clot risk factors that combined may cause runners to experience a DVT.  One good example is the publicized case of Serena Williams, who experienced a pulmonary embolism (a blood clot lodged in the lung, typically originating from a DVT) after the combination of a foot injury, surgery, and cross-country flight.

This year, we’re investigating this “perfect storm hypothesis” further at the 2015 Boston Marathon by looking at women who fly to and from the marathon and also use estrogen-based oral contraceptives. Oral contraceptive use alone increases the risk of venous thrombosis five-fold and is commonly used by female athletes. Since 75% of female marathon finishers are of child-bearing age, increasing numbers of female runners will be exposed to this potential combination of risk factors. Funded by a NASA CT Space Grant Consortium Fellowship Program grant, we have enrolled 15 women who are on oral contraceptives and also flying from California to run the 2015 Boston Marathon. We’ll also study a travel only group (women on oral contraceptives flying cross-country but not running a marathon) and a control group (women on oral contraceptives neither flying nor running), looking at markers of clot formation and breakdown after air travel, marathon running, and/or control conditions. Sounds complicated, right? It is…but the great thing about doing research in a population of runners is how willing they are to invest in research related to health and wellness. For example, the initial e-blast that went out to registered runners to help us recruit yielded 146 replies from women interested in participating! Stay tuned for results and updates…

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