Physical activity and risk of inflammatory bowel disease: prospective study from the Nurses' Health Study cohorts.

OBJECTIVE: To examine the association between physical activity and risk of ulcerative colitis and Crohn's disease.

DESIGN: Prospective cohort study.

SETTING: Nurses' Health Study and Nurses' Health Study II.

PARTICIPANTS: 194,711 women enrolled in the Nurses' Health Study and Nurses' Health Study II who provided data on physical activity and other risk factors every two to four years since 1984 in the Nurses' Health Study and 1989 in the Nurses' Health Study II and followed up through 2010.

MAIN OUTCOME MEASURE: Incident ulcerative colitis and Crohn's disease.

RESULTS: During 3,421,972 person years of follow-up, we documented 284 cases of Crohn's disease and 363 cases of ulcerative colitis. The risk of Crohn's disease was inversely associated with physical activity (P for trend 0.02). Compared with women in the lowest fifth of physical activity, the multivariate adjusted hazard ratio of Crohn's disease among women in the highest fifth of physical activity was 0.64 (95% confidence interval 0.44 to 0.94). Active women with at least 27 metabolic equivalent task (MET) hours per week of physical activity had a 44% reduction (hazard ratio 0.56, 95% confidence interval 0.37 to 0.84) in risk of developing Crohn's disease compared with sedentary women with <3 MET h/wk. Physical activity was not associated with risk of ulcerative colitis (P for trend 0.46). The absolute risk of ulcerative colitis and Crohn's disease among women in the highest fifth of physical activity was 8 and 6 events per 100,000 person years compared with 11 and 16 events per 100,000 person years among women in the lowest fifth of physical activity, respectively. Age, smoking, body mass index, and cohort did not significantly modify the association between physical activity and risk of ulcerative colitis or Crohn's disease (all P for interaction >0.35).

CONCLUSION: In two large prospective cohorts of US women, physical activity was inversely associated with risk of Crohn's disease but not of ulcerative colitis.