Plasma 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D and risk of incident ovarian cancer.

A194

Few modifiable factors are known to reduce risk of ovarian cancer. Experimental data and ecologic studies suggest that vitamin D may reduce ovarian cancer risk. Therefore we examined whether plasma concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were associated with risk of epithelial ovarian cancer in a nested-case control study using data from three prospective cohort studies: the Nurses' Health Study (NHS), NHSII, and the Women's Health Study (WHS). The analysis consisted of 224 cases (161 from NHS/NHSII and 63 from WHS) and 606 controls (matching case:control ratio 1:3 for NHS/NHSII and 1:2 for WHS). Multivariate relative risks (RR) and 95% confidence intervals (CI) were adjusted for ever use of postmenopausal hormones, body mass index (BMI) at blood draw, parity, lactose intake, duration of oral contraceptive use, and season of blood draw. Women ranged in age from 34 to 73 years old (mean=56 years). Overall, we did not observe significant associations between 25-hydroxyvitamin D (RR, top vs. bottom quartile=0.85, 95% CI=0.51-1.41, p-trend=0.63) or 1,25-dihydroxyvitamin D levels (corresponding RR=1.14, 95%CI=0.71-1.85, p-trend=0.93) and ovarian cancer risk. Study-specific associations also were not statistically significant and there was no statistical heterogeneity between studies (p=0.59 for 25-hydroxyvitamin D and 0.42 for 1,25-dihydroxyvitamin D). However, there was a significant inverse association among overweight and obese women for 25-hydroxyvitamin D levels (RR, top vs. bottom quartile=0.39, 95% CI=0.16-0.94, p-trend=0.05). Further, among all women, those with adequate (>=32 ng/mL) versus inadequate 25-hydroxyvitamin D levels had a modestly decreased risk of serous ovarian cancer (RR=0.66, 95% CI=0.40-1.08). Among overweight and obese women, those with adequate 25-hydroxyvitamin D had a 52% decreased risk of ovarian cancer (95% CI=0.22-1.04) compared to those with inadequate levels. Overall, our results do not suggest that plasma vitamin D levels are associated with risk of ovarian cancer. However, we did observe significant associations in some subgroups, which should be evaluated further in other studies since increasing vitamin D intake is an easy preventive measure to adopt.