Physical Inactivity Doubles Pulmonary Embolism Risk in Women

Laurie Barclay, MD

July 05, 2011

July 5, 2011 — Women who sat for long periods of time every day were 2 to 3 times more likely to develop idiopathic pulmonary embolism than more active women, according to the results of a prospective cohort study published online July 4 in the British Medical Journal.

"Associations between physical inactivity, physical activity, and pulmonary embolism remain uncertain," write Christopher Kabrhel, MD, attending physician and assistant professor of surgery, Department of Emergency Medicine, Massachusetts General Hospital, Boston, and colleagues.

"Some published case-control studies found that exercising on a regular basis decreases the risk of venous thrombosis by 30-50% compared with not exercising. Other studies, however, including prospective cohort studies, have found that physical activity is associated with an increased risk of venous thromboembolism."

Using the Nurses' Health Study cohort of 69,950 female nurses who completed biennial questionnaires from 1990 to 2008, the investigators aimed to examine the association between sedentary lifestyle and incident idiopathic pulmonary embolism. The main study endpoint was idiopathic pulmonary embolism documented by medical records review.

Using multivariable Cox proportional hazards models, the investigators controlled for age, body mass index, energy intake, smoking status, pack-years, race, spouse's educational level, parity, menopause, nonaspirin nonsteroidal anti-inflammatory drugs, warfarin, multivitamin supplements, hypertension, coronary heart disease, rheumatological disease, and dietary patterns. The main exposure evaluated was physical inactivity (hours of sitting per day), and the secondary exposure was physical activity (metabolic equivalents per day).

There were 268 episodes of incident idiopathic pulmonary embolism during the 18-year study period. Time spent sitting each day was directly associated with risk for idiopathic pulmonary embolism (in combined data, 41/104,720 for the most inactive women compared with 16/14,565 for the least inactive women; P < .001 for trend).

Compared with women who spent the least time sitting, women who spent the most time sitting had more than double the risk for pulmonary embolism (multivariable hazard ratio, 2.34; 95% confidence interval, 1.30 - 4.20). Physical activity was not associated with pulmonary embolism (P = .53 for trend).

"Physical inactivity is associated with incident pulmonary embolism in women," the study authors write. "Interventions that decrease time sitting could lower the risk of pulmonary embolism."

Limitations of this study include its low generalizability to nonwhite racial/ethnic groups, to men, and to younger women; use of self-reported time sitting as a proxy measure for physical inactivity; and inability to detect any changes in physical inactivity. Other limitations were failure to control completely for warfarin use, measurement bias, investigation bias, and reliance on self-report for measurement of physical inactivity.

In an accompanying editorial, James D. Douketis, MD, and Alfonso Iorio, MD, from McMaster University in Hamilton, Ontario, Canada, note that the findings, if valid, may have major public health implications.

"Overall, the study reinforces the notion that prolonged inactivity increases the risk of [venous thromboembolism], and it shows how this occurs in everyday life," Dr. Douketis and Dr. Iorio write. "The findings also indirectly support the use of preventive interventions for at risk people with prolonged immobility, typically patients in hospital, in whom anticoagulants to prevent [venous thromboembolism] remain underused. For otherwise healthy people, the take home message may be to apply the ancient Greek proverb of 'métron áriston' or 'moderation is best' to both our activity and inactivity."

The National Institute on Aging, National Institutes of Health, Bethesda, Maryland, supported this study. The study authors and editorialists have disclosed no relevant financial relationships.

BMJ. Published online July 4, 2011. Article Full text Editorial Extract

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