Outrun Danger: Why Fit Women Get Blood Clots
The XX Factor
Younger women should be especially vigilant -- those under 45 are about 30 percent more likely to have blood clots than men of the same age. The main reason: hormonal birth control, which can increase the odds of clots by two to eight times. Researchers suspect that elevated levels of estrogen and progesterone in these contraceptives may be to blame.
Jenny used a vaginal ring, as did Kara King, 38, who was diagnosed with blood clots in her left leg and lungs in 2010. Kara's first clue was a cramp deep in her calf that wouldn't go away. As someone who did aerobics regularly and walked a couple of miles a day, though, she blew it off as a pulled muscle. A week later her leg ballooned so much that she could barely see her kneecap. "My leg was turning purple and felt as if it were going to burst," says Kara, who lives in Bee Cave, Texas. She spent five terrifying days in an intensive care unit undergoing treatment. Now she can't make it through an aerobics class because her leg starts to ache, and she will be taking blood thinners indefinitely. "I'll live with the scars of this forever," she says.
Pregnant and postpartum women are at increased risk of blood clots; estrogen is probably a factor. The threat is 100 times greater in the first week after delivery and 20 to 80 times higher during the first six weeks, as the body works to patch and repair the vessels affected by the delivery.
Surgery can also lead to blood clots. People who are operated on -- particularly if they have pelvic, abdominal, hip, or knee surgery -- are 22 times more likely to get a clot, because veins can be damaged during the procedure and patients spend so much time lying in bed afterward. That was the case for Samantha Shelton, the FITNESS assistant Web editor. At age 18, she was recovering from knee surgery to repair a soccer injury when ER docs discovered seven blood clots in her left leg. Samantha learned she had another, more under-the-radar risk factor for clots: a genetic blood disorder called factor V Leiden. Such disorders affect an estimated 5 to 8 percent of people in the United States, many of whom are unaware of them. "After my diagnosis, my family got tested, and we found out it comes from my father's side," Samantha, now 23, says. "I was on the Pill because I had bad acne, and my doctor later told me that if I had been a smoker, I would have developed a clot within a month. Now I can't take anything hormonal."
In many cases, several risk factors stack up, creating the perfect storm for a clot. Jenny had two strikes against her. In addition to using birth control, she spent hours in the air, traveling to and from races. Flights lasting four hours or longer more than triple the risk of blood clots; the longer the flight, the greater the risk. Several flights in a short period up the odds as well. Back-to-back exercise and air travel may also put athletes in danger: Runners who flew more than four hours to the 2010 Boston Marathon had higher levels of an enzyme that can cause clotting compared with those who drove less than two hours, one study found.
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