Physical activity and risk of endometrial adenocarcinoma in the Nurses' Health Study.

Studies suggest that greater physical activity may reduce endometrial cancer risk. However, the role of the timing, duration and intensity of activity is unclear. We therefore examined recent and past recreational activities in relation to incident endometrial adenocarcinoma, and compared the importance of total and moderate- or vigorous-intensity activities as well as walking. We analyzed data from 71,570 women in the Nurses' Health Study, a prospective cohort that assessed activity in 1986, with updates every 2-4 years. Cox proportional hazards models were used to estimate relative risks (RRs) and 95% confidence intervals (CIs). During follow-up from 1986 to 2008 (1.2 million person-years), 777 invasive endometrial adenocarcinoma cases were documented. In multivariable models, compared with <3 MET-hr/week (<1 hr/week walking), women engaged in moderate (9 to <18 MET-hr/week: RR = 0.61, 95% CI: 0.48-0.78) or high (≥27 MET-hr/week: RR = 0.73, 95% CI: 0.58-0.92) amounts of recent total recreational activity were at reduced risk (p-trend = 0.001). Past total activity was not associated with risk. Greater recent moderate- or vigorous-intensity activity was associated with reduced risk (≥4 vs. 0 hr/week: RR = 0.65, 95% CI: 0.47-0.88, p-trend = 0.002). Among women who did not perform any vigorous activity, recent walking was associated with reduced risk (≥3 vs. <0.5 hr/week: RR = 0.65, 95% CI: 0.45-0.93, p-trend = 0.01), and faster walking pace was independently associated with risk reduction. After additional adjustment for body mass index, all associations were statistically non-significant. Greater recent physical activity, including activity of moderate duration and intensity such as walking, may reduce endometrial adenocarcinoma risk. This relation is largely mediated or confounded by body mass index.