OBJECTIVES:

To determine the association between physical inactivity (that is, a sedentary lifestyle) and incident idiopathic pulmonary embolism.

DESIGN:

Prospective cohort study.

SETTING:

Nurses' Health Study.

PARTICIPANTS:

69 950 female nurses who completed biennial questionnaires from 1990 to 2008. Main outcome measures The primary outcome was idiopathic pulmonary embolism confirmed in medical records. Multivariable Cox proportional hazards models controlled for age, body mass index (BMI), energy intake, smoking, pack years, race, spouse's educational attainment, parity, menopause, non-aspirin non-steroidal anti-inflammatory drugs, warfarin, multivitamin supplements, hypertension, coronary heart disease, rheumatological disease, and dietary patterns. The primary exposure was physical inactivity, measured in hours of sitting each day. The secondary exposure was physical activity, measured in metabolic equivalents a day.

RESULTS:

Over the 18 year study period, there were 268 cases of incident idiopathic pulmonary embolism. There was an association between time of sitting and risk of idiopathic pulmonary embolism (41/104 720 v 16/14 565 cases in most inactive v least inactive in combined data; P<0.001 for trend). The risk of pulmonary embolism was more than twofold in women who spent the most time sitting compared with those who spent the least time sitting (multivariable hazard ratio 2.34, 95% confidence interval 1.30 to 4.20). There was no association between physical activity and pulmonary embolism (P=0.53 for trend).

CONCLUSIONS:

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