Body size in early life and risk of epithelial ovarian cancer: results from the Nurses' Health Studies

Adult body mass index (BMI) has been associated with ovarian cancer risk, but few studies have examined body size earlier in life. We prospectively examined associations of body fatness at ages 5 and 10, BMI at age 18, height, and birthweight with risk of epithelial ovarian cancer in the Nurses' Health Study (NHS: 110 311 women, 735 cases) and Nurses' Health Study II (NHSII: 113 059 women, 137 cases). Cox proportional hazards regression was used to estimate relative risks (RRs) and 95% confidence intervals (CIs). There was a weak inverse association between average body fatness at ages 5 and 10 and risk in the NHS (RR for heaviest vs most lean = 0.81, 95% CI: 0.53-1.24, P for trend = 0.04) and a nonsignificant positive association in the NHSII (RR = 2.09, 95% CI: 0.98-4.48, P for trend = 0.10), possibly due to differences in age and menopausal status. Height was positively associated with risk in both cohorts (RR for >= 1.75 vs <1.6m = 1.43, 95% CI: 1.05-1.96, P for trend = 0.001). Body mass index at the age of 18 years and birthweight were not associated with risk. Further research should examine the biological mechanisms underlying the observed associations.