Serum 25-hydroxyvitamin D and the risk of ovarian cancer

Introduction: Ecological and experimental studies suggest that vitamin D may be associated with a reduced risk of ovarian cancer. In this study, we sought to determine the risk of developing ovarian cancer according to serum 25-hydroxyvitamin D (25-OHD) concentrations assessed on average 5 years before the diagnosis. Methods: We conducted a population-based longitudinal case-control study nested within the Finnish Maternity Cohort (FMC) which contains serum samples of virtually all pregnant women in Finland since 1983. Among them, 201 ovarian cancers diagnosed within 10 years of serum sampling were randomly selected as cases for this study. For each case, we selected two controls matched for age, parity and sampling season (±4 weeks) and one control matched for age and parity but for the opposite sampling season (6 months ± 4 weeks). Results: The relative risks (estimated as odds ratio, OR) for ovarian cancer comparing the lowest quintile to the highest quintile of serum 25-OHD concentration were 1.8 (95% CI 0.9-3.5) among controls matched for the same season, and 1.1 (95% CI 0.6-2.2) among controls matched for the opposite season. The OR among women with insufficient (<75 nmol/L) serum 25-OHD concentration was 2.7 (95% CI 1.0-7.9, lower limit, 0.95) compared to that among those with sufficient (≥75 nmol/L) serum 25-OHD concentration. No differences in the point estimates were observed between serous or mucinous histological subtypes of ovarian cancer. Conclusion: Overall, we did not observe a significant association between serum 25-OHD concentrations and the risk of ovarian cancer. However, we found evidence suggestive of an increased risk among women with low to insufficient serum 25-OHD concentrations.