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Lung Disease & Respiratory Health Center

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Sitting for Long Time Linked to Pulmonary Embolism

Study Suggests Excessive Sitting May Increase the Risk for Blood Clots in the Lungs


In contrast, excessive sitting -- in this case, for nearly six hours each day on average -- increased the annual risk of having a pulmonary embolism from one or two out of every 1,000 adults to one or two in 500 adults.

Douketis points out that the risk from sitting appears to be slightly higher than the risk of blood clots associated with taking birth control pills and about half the risk of getting blood clots that a woman faces during pregnancy.

The study is published in BMJ.

"It's a nice study," says Jack E. Ansell, MD, chairman of medicine at Lenox Hill Hospital in New York City and an expert on thrombosis, or the formation of blood clots.

"There are always limitations to a retrospective review of this nature, but the findings look fairly definite," Ansell tells WebMD. "It provides further, additional evidence that inactivity can be harmful."

Sitting and the Risk of Pulmonary Embolism

For the study, researchers combed through data collected by the Nurses' Health Study, a long-running investigation that's collecting information about the health of thousands of registered female nurses in the U.S.

The study collects information about lifestyle habits as well as any newly diagnosed diseases every two years by questionnaire.

Nearly 70,000 women were included in the current research. Their average age in 1990 was 56.

Researchers split them into groups based on how much time they said they spent sitting down each day.

About 43% of women reported sitting less than 10 hours each week in their leisure time, 52% reported sitting between 11 and 40 hours each week, and 5% reported sitting for at least 41 hours each week.

Over 18 years, there were 268 cases of pulmonary embolism that didn't have a known cause.

Even after controlling for variables known to be associated with the risk of lung blood clots, researchers found that women who were the most physically inactive had a rate of pulmonary embolism that was 2.34 times higher than women who reported sitting the least.

In a separate analysis that looked at how much exercise the women reported, researchers found no association between physical activity and the risk for pulmonary embolism, suggesting that it was the hours they spent sitting, rather than the hours they spent exercising that counted more -- a phenomenon that's been noted in other studies.

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