Extensive sitting increases women’s risk of  pulmonary embolism, finds a new study  in the current issue of the British Medical Journal. Women who reported the most inactivity were about twice as likely to experience pulmonary embolism as women reporting the least amount of inactivity. A generally inactive lifestyle increases the risk of a pulmonary embolism, which  occurs when a substance, usually a blood clot, travels through the bloodstream and lodges in the main artery leading to the lungs. About one-third of those untreated for their pulmonary embolism die from the condition, according to the Mayo Clinic.

Dr. James Douketis, director of Vascular Medicine at McMaster University, points out that the increased risk of pulmonary embolism for any one individual from extensive sitting is relatively small – only slightly higher than the risks of using oral contraceptives – and that the findings fit into a “common sense” recommendation that people spend less time in sedentary positions.

The authors join other researchers in recommending that public health campaigns target physical inactivity, not just promote physical activity.

The most at-risk group was composed of women sitting for more than 41 hours a week outside of work, while the least at-risk group sat for less than 10 hours a week. Time spent sitting at work was not factored into the study.

Physical activity did reduce the risk for some women when compared with their peers who sat for similar amounts of time, but exercised less.

Researchers used 18 years of data from a longitudinal study of 69,950 female nurses which began in 1976, and was subsequently updated in 1988 to include questions about inactivity at home.

About 90% of the participating women were white, which reflects the demographics of women in nursing when the study began, notes the study authors.