You can be uber-fit and still suffer from this health threat that affects almost a quarter-million women


Jenny Fletcher should have been at the top of her game. In the fall of 2012, the triathlete and former model had scored her first victory in a half-Ironman, just three years after turning pro. But seven months later, in April 2013, she found herself struggling to cross the finish line at an all-woman half-marathon in New York City. "After the race, I was nauseous and had to sit down," Jenny, 37, says. "I ended up back in my hotel room, sleeping all day."

Things got worse when she went home to Los Angeles: Jenny awoke on the night of her return with a stabbing pain in her rib cage. Out cycling a few days later, her breathing was so labored that she lagged behind her training partners. And after a tough pool workout, she curled up on her couch with a massive headache, in tears, barely able to move. What's wrong with me? she wondered. Still, she convinced herself that she was just tired or stressed out. (BTW, these 11 foods can help lower your stress levels naturally.) "I got off my couch and did a hard bike ride," Jenny recalls. "As an athlete, I'm trained to push through pain."

When she coughed up blood the next morning, it scared her enough to finally see a doctor. A CT scan led to a shocking discovery: Jenny had blood clots from working out throughout her lungs, almost entirely blocking her right pulmonary artery. "The doctor told me that if I had waited one more day to come in, I might not be alive," Jenny says. (Related: I'm a Young, Fit Spin Instructor-and Nearly Died of a Heart Attack)

After shots of a powerful medicine to break up the clots and an overnight hospital stay, Jenny went home with the prognosis that she would be on blood thinners and unable to race for at least six months—and with a question that kept nagging at her: How could this have happened to me and why, if I’m so healthy, am I struggling with blood clots from working out?

The Hidden Risk of Blood Clots from Working Out

Most of us associate blood clots with having major surgery, smoking or being elderly or overweight. But the truth is, they can strike anyone, even fit women, says Stephan Moll, M.D., the medical director of the University of North Carolina at Chapel Hill's blood clot education outreach program, Clot Connect. In fact, about a quarter million women suffer from dangerous blood clots (from working out or otherwise) every year.

Typically, clotting is a good thing. It's the body's natural protective response when a blood vessel is injured during an accident or an operation. Think of it as patching a crack in drywall. "That's what our bodies do with damaged blood vessels," says Andra H. James, M.D., an ob-gyn and advisory board member of the nonprofit National Blood Clot Alliance.

Clots can also occur, however, when the blood circulates sluggishly during long stretches of inactivity, like sitting on a plane or in a car; when hormone levels are elevated; or because of a blood disorder. If the clot doesn't dissolve on its own, it may grow in a deep vein in the body—a condition known as deep vein thrombosis (DVT)—where it obstructs the circulation of blood from the extremity back to the heart. About 90 percent of the time, DVT forms in the legs. In more than 30 percent of cases, the clot (or a piece of it) breaks off and travels to the lungs, causing a blockage in the artery there. This is known as a pulmonary embolism (PE). When the lung clot is large or there are many small ones, the heart has to work especially hard to pump. Untreated, the pressure becomes too great and the heart stops. (Related: What’s Causing That Tightness in Your Chest?)

What Are the Symptoms of Blood Clots?

Both DVT and PE have warning signs. In DVT, the affected leg may become painful, swollen, red or blue, or feel warm to the touch. PE often causes chest pain, coughing or shortness of breath. Yet it's easy to dismiss these blood clot symptoms as everyday workout aches. "Fit women may think they have a charley horse or a twisted ankle or that their chest pain is due to a muscle strain," says Dr. Moll.

That can be a fatal mistake. As many as 100,000 people a year die from DVT/PE in the United States—more than the number of deaths from breast cancer, HIV, and car accidents combined—according to the Centers for Disease Control and Prevention. "Women need to be aware of the symptoms of DVT/PE and seek medical attention immediately if they have any of them," says John A. Heit, M.D., a professor of medicine at the Mayo Clinic College of Medicine in Rochester, Minnesota.

Why Women are More Likely to Get Blood Clots from Working Out

Hormonal Birth Control

Hormonal birth control plays a big role. 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. (See one woman's experience here: My Birth Control Almost Killed Me)

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. (More on this, here: What's the Deal with Birth Control and Blood Clots?)


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, a former Shape 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." (Migraines with aura can be sign you're at risk, too.)

In many cases, several risk factors stack up.

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.

Kara now realizes that it should have been a red flag three years ago when her leg pain didn't improve with rest and ibuprofen. "My biggest mission now is to tell people that the pain in your leg can kill you," she says. "You need to pay attention to it and get help."

How to Protect Yourself from Blood Clots

Fortunately, you don't need to ditch birth control or swear off flying to prevent blood clots. Instead, follow these simple steps.

  • Stay active. The longer you sit still, the more sluggish your blood flow and the greater the chance of a clot. If you have a desk job, tapping your toes or bouncing your knee at least every hour will contract your calf muscles and kick-start circulation, says Christopher Kabrhel, M.D., a professor of emergency medicine at Harvard Medical School. Exercise lowers the risk of clots even if you're mostly sedentary, he adds, so hit the gym after a long workday.
  • Choose the aisle seat on planes. You'll be more apt to stand up and stretch your legs, which will get your blood pumping. Also, take catnaps instead of conking out for the entire flight; your lungs are more efficient at taking in oxygen—and therefore your circulation is better—when you're awake. If you're flying before or after a hard workout or race, wear compression socks and loose clothing and stay hydrated.
  • Check out your birth control. Does it contain drospirenone, a synthetic version of progesterone? Newer pills that do, such as Yaz and Yasmin, pose two to three times the risk of DVT/PE than older oral contraceptives with levonorgestrel, a different synthetic progestin, two recent studies found. Vaginal rings and skin patches double the odds of getting a blood clot compared with the lower-risk pills, according to a Danish study, possibly because the amount of estrogen absorbed from patches is 60 percent higher than the amount delivered by oral contraceptives. While the absolute risk of a blood clot is still small for the average woman on birth control, it pays to take precautions, says ob-gyn Dr. James. When choosing a contraceptive, discuss with your doctor any other blood clot risk factors you have—such as being over age 35, a smoker, overweight, or having a family history of DVT/PE—and then consider the odds. Readdress birth control with your doc if your risk factors change in the future, especially if you're immobilized or have an injury, Dr. James says. And in that case, consider switching to a progestin-only IUD, like Mirena or Skyla, or a mini-Pill, neither of which raises blood clot risk. (Don’t fall for these common birth control myths.)
  • Speak up. If you will be undergoing surgery, ask your doctor what precautions he is going to take to protect you from blood clots. And if you're on hormonal birth control, tell the surgeon. She may suggest that you go off it temporarily.
  • Watch your left leg when you're pregnant. Researchers at the University of Toronto found that of the 124 cases of pregnant women with DVT that they studied, nearly 90 percent had the condition in their left leg. During pregnancy, more blood clots occur in the left leg because an artery overlying a vein there obstructs blood flow. If your left leg hurts, swells, or turns red suddenly, all signs point to a clot. See your physician immediately or go to the ER. To prevent clots after delivery, walk around as much as possible as soon as your doctor says it's OK.
  • Interview your family. Have your grandparents, parents, or siblings had DVT/PE? A family history of the condition puts you at a somewhat increased risk, so inform your M.D.
  • Treat varicose veins. Blood flows more slowly through an enlarged vein, increasing clot risk sixfold. Talk to a vascular surgeon about removing any bulging veins, or ask your doctor for a prescription for medical support hose to help prevent clots. (Related: Does Weight Lifting Cause Varicose Veins?)
  • Listen to your body. "If something feels wrong, have it checked out," Dr. Moll says.