Adolescent physical activity and endometriosis risk.

Background: In the one study examining the relationship, adolescent physical activity was not associated with risk for endometriosis. Case-control studies have shown 40-80% reductions in risk for adult activity, while only an 11% reduction in endometriosis risk was observed in a recent prospective analysis.

Methods: Using data collected from the Nurses' Health Study II, a prospective cohort study of premenopausal US nurses that began in 1989, we have attempted to clarify this relation. Data are updated every 2 yrs with follow-up for these analyses through to 2001. Women reported the average amount of time per week spent in moderate and strenuous recreational activity during three age periods: ages 12-13, ages 14-17, and ages 18-22. A metabolic equivalent (MET) score was assigned to each activity and these were summed to estimate total activity.

Results: During 637,747 person-years of follow-up, 1,481 cases of laparoscopically confirmed endometriosis were reported among women with no past infertility. After adjusting for age, calendar time, birth weight, age at menarche, parity, oral contraceptive use, and body mass index (BMI), we observed a 16% increase in the risk for endometriosis comparing the greatest amount of activity (≥80 MET-h/wk) with the least (<20 MET-h/wk) during ages 12-13 (RR=1.16, 95% CI=0.98-1.37, p-value test for trend=0.02), and no associations for ages 14-17 or ages 18-22. In analyses of the individual activity types within each time period, only strenuous activity during ages 12-13 was associated with endometriosis.

Conclusions: We did not find evidence of a beneficial association between adolescent physical activity and laparoscopically confirmed endometriosis, but in fact found a small increase in risk.