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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

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.

The study also showed that women who were more physically inactive had more heart disease and hypertension than those who reported being more active at home.

The study has some important limitations.

Because the Nurses' Health Study only asked about sitting in a couple of the questionnaires, the researchers had to assume that the women in the study kept the same habits they reported in 1990 over the 18-year period of observation.

Douketis points out that personal habits like sitting aren't steady exposures. People can decide to be more active, or they may become more inactive over time in response to worsening health.

And even though the study took into account a number of important variables, epidemiologists know that it's impossible to take into account all the factors that may be at work.

For example, women who reported being most inactive in the study showed associations with heart disease even in the early years of the study, raising the question of whether physical inactivity was a trigger or a consequence of an already present disease.

Even with all those caveats, experts say it would be wise for people who find themselves sitting on the sofa, or really sitting in any setting for hours at a time -- a car, a plane, a desk -- to get moving.

"It's the same thing that I would recommend for people who fly on airplanes where you're in somewhat cramped conditions for long periods of time," Ansell says. "Get up and move about, if you can. At least do some leg and foot exercises to keep the blood flowing."

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