Experimental evidence and ecologic studies suggest a protective role of
vitamin D in ovarian
carcinogenesis. However, epidemiologic studies using individual level data have been inconsistent. We evaluated ultraviolet (UV)-B radiation,
vitamin D intake, and predicted plasma
25-hydroxyvitamin D [25(
OH)D] levels as long-term surrogates of
vitamin D exposure within the Nurses' Health Study (NHS) and NHSII. We estimated incidence rate ratios (RRs) and 95% confidence intervals (CIs) for risk of overall
ovarian cancer and by histologic subtype using Cox proportional hazards models. Between 1976 and 2010 in NHS and 1989 and 2011 in NHSII, we identified a total of 1,225 incident
epithelial ovarian cancer cases (NHS: 970, NHSII: 255) over 4,628,648 person-years of follow-up. Cumulative average UV-B exposure was not associated with
ovarian cancer risk in NHS (Ptrend = 0.08), but was associated with reduced risk in NHSII (highest vs. lowest category RR = 0.67; 95% CI: 0.50, 0.89; Ptrend < 0.01). When stratified by histologic subtype, UV-B flux was positively associated with risk of serous
tumors in NHS (Ptrend < 0.01), but inversely associated in NHSII (Ptrend = 0.01). Adjusted for confounders,
ovarian cancer risk was not associated with
vitamin D intake from food or supplements or with predicted 25(
OH)D levels. Our study does not strongly support a protective role for
vitamin D in
ovarian cancer risk.