Moderate-to-vigorous physical activity and leisure-time sitting in relation to ovarian cancer risk in a large prospective US cohort.

PURPOSE: Physical activity is hypothesized to lower the risk of ovarian cancer, but current evidence for an association is limited and inconclusive. The purpose of this study was to examine moderate-to-vigorous physical activity, walking, and leisure-time sitting in relation to incident ovarian cancer, overall and by histologic subtype.
METHODS: Moderate-vigorous recreational physical activity (MET-hours/week), recreational walking, and leisure-time sitting were examined in relation to epithelial ovarian cancer in the American Cancer Society Cancer Prevention Study II Nutrition Cohort, a US cohort followed for cancer incidence from 1992 to 2011. Exposure information was collected via self-administered questionnaires. Cox proportional hazards regression was used to estimate multivariable-adjusted relative risks (RRs) and 95% confidence intervals (CIs) of total, serous, and nonserous ovarian cancer according to MET-hours/week, hours/week of walking, and hours/day of sitting.
RESULTS: Among 63,972 postmenopausal women, 651 cases of ovarian cancer were identified during follow-up. Neither MET-hours/week nor walking was associated with risk. However, ≥6 h/day of sitting, compared to <3, was associated with higher risk of ovarian cancer (RR 1.44, 95% CI 1.12-1.85), particularly for serous cancer (RR 1.52, 95% CI 1.06-2.16), although statistical heterogeneity by histology was not detected (p = 0.36).
CONCLUSIONS: Results from this study do not support an association between physical activity and ovarian cancer, whereas prolonged sitting may be associated with higher risk. Additional large studies are needed to further assess possible etiologic differences by histologic subtype.