Blood Clot Hazard—Don’t Sleep Like This

It took an earthquake to reveal that your car might put you at a higher risk for blood clots than a long trip by plane.    

In April 2016, after a Richer 7 earthquake hit Kumamoto, Japan, thousands fled the area. A dam was at risk of failing, aftershock tremors made it too dangerous to return home for days afterward. Shelters quickly filled.   

Some people, with nowhere else to go, slept in their cars. Everyone waited for the situation to safe enough for the all clear to return home.

Over the next few days after the quake hit, local hospitals admitted 51 patients with blood clots. The number was so much higher than usual doctors wanted to know why—was it the quake, the fears, something else? Those questions led to KEEP—the Kumamoto Earthquake Thrombosis and Embolism Protection study.

When the KEEP team asked patients what they had been doing in the days before they came to the hospital with new blood clots, they discovered that 82% (42 out of 51 patients) had spent a night in their car.

More surprising, and definitely more worrisome, in 35 of these car-sleepers, the embolism moved into their lungs as a venous thromboembolism (VTE).

VTE’s are life-threatening. But the most scary thing about them is that they often have no symptoms and cause no pain, so they go untreated. As Tampa Cardiovascular Associates, a specialty practice, puts it—“the first visible symptom is often sudden death.”

Sleeping Anywhere Else Is Better

The link between sleeping in a cramped car and a VTE was doubly confirmed in the KEEP study by the nine people who got clots but had not slept in their cars. Among these, only three (33%) developed a VTE compared to 83% of the people who got clots after sleeping in their cars.

What Is the Blood Clot-Travel Risk to You?

You may never need to sleep in your car after running from an earthquake. We hope not. But you probably do fly sometimes. And like sleeping in a car overnight, long flights are clot breeders because they keep you in a cramped position with little or no movement. That causes blood to pool in the veins, inviting clots to form.

But this risk is one you can mitigate.

Here's what doctors at the Centers for Disease Control in the US and the National Health Service in Britain say:

You might be at risk for a DVT or VTE even if you've never had a clot before. Immobility has a damaging effect on everyone’s circulation. But if you are subject to clots for some additional reason, your risk becomes very high.

Your risk is higher than average if


  • you smoke
  • have cancer
  • have had recent surgery in the pelvic area or legs
  • have varicose veins
  • are obese
  • have any history of heart disease.

For women your risk is also higher if


  • you are pregnant
  • you are using hormone replacement therapy
  • you are using estrogen-containing birth control.

If your parents or close family members have a history of blood clots, there’s also a possibility of genetic clotting disorder. Your own doctor can talk to you about that. A family history is an important clue, and special medical tests can reveal certain genetic profiles including the most common gene sequences implicated in deep vein thrombosis (DVT’s) and VTE’s.

Good Practices to Beat Bad Clots

Deaths by VTE’s are the third leading cause of deaths due to vascular problems, right behind heart attacks and strokes.

Fortunately, there’s a lot you can do to manage your risk, even if you have a genetic propensity for clotting.

Dress comfortably in loose clothing.

Avoid alcohol or sleeping pills (yeah, we know), and drink plenty of water.

Also, consider compression stockings if your legs tend to swell or feel extra tired after inactivity and travel. NHS recommends a 14-17 mmHg pressure at the ankle. That's a low to moderate amount of compression. NHS also notes that these stockings need to be measured and fitted correctly or you could increase your risk of a deep vein thrombosis.

Your second line of defense on the plane, train, or in your car, if you really must sleep there, is to get some movement.

When possible, stand for a while once per hour, and walk around a bit if you can. On a plane, an aisle seat is best if you can snag one.

But no matter what, do some leg exercises. The simplest one is ankle circles. Also, stretch your legs and flex your ankles (pull them toward you).

The reason for comfy clothes, and pants, in particular, is that you might want to do this one more exercise sometimes recommended by the airlines. Grab one knee with both hands and pull it up toward your chest. Hold for a count of 15. Repeat 10 times. Then do the other leg.

That's not something we recommend in a dress or a kilt. Bon voyage!

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