Abstract
Emerging data suggest that exposures in early life may affect ovarian development and contribute to ovarian cancer risk. We evaluated the association between early life physical activity and risk of ovarian cancer in adulthood in two large prospective cohorts, the Nurses' Health Study (NHS) and NHSII. In total, analyses included 28 232 NHS participants (followed from 2004 to 2016) and 56 553 NHSII participants (followed from 1997 to 2017). Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for risk of ovarian cancer overall and by early life body mass index (BMI). Neither physical activity at ages 12-13, 14-17 or 18-22 years nor average physical activity across these three periods was associated with ovarian cancer risk overall (≥78 vs <24 MET-h/wk, HRs = 1.34, 1.21, 1.08 and 1.24, respectively), or by categories of early life BMI (P(heterogeneity) ≥ .44). No association was observed with the risk of high-grade serous or poorly differentiated tumors or postmenopausal ovarian cancer. Overall, early life physical activity was not clearly related to ovarian cancer risk during adulthood.