Serum 25-hydroxyvitamin D and risk of post-menopausal breast cancer - results of a large case-control study

Various studies suggest that vitamin D may reduce breast cancer risk. Most studies assessed the effects of dietary intake only, although endogenous production is an important source of vitamin D. Therefore, the measurement of serum 25-hydroxyvitamin D [25(OH)D] better indicates overall vitamin D status. To assess the association of 25(OH)D serum concentrations with post-menopausal breast cancer risk, we used a population-based case-control study in Germany, which recruited incident breast cancer patients aged 50-74 between 2002 and 2005. Information on sociodemographic and breast cancer risk factors was collected by personal interview. For this analysis, we included 1394 cases and 1365 controls, matched on year of birth and time of blood collection. Conditional logistic regression was used to calculate odds ratios (ORs) for breast cancer adjusted for potential confounders. Serum 25(OH)D concentration was significantly inversely associated with post-menopausal breast cancer risk. Compared with the lowest category (< 30 nM), OR [95% confidence intervals (CI)] for the higher categories of 25(OH)D (30-45, 45-60, 60-75 and >= 75 nM) were 0.57 (0.45-0.73), 0.49 (0.38-0.64), 0.43 (0.32-0.57) and 0.31 (0.24-0.42), respectively (P-trend < 0.0001). Analysis using fractional polynomials indicated a non-linear association. The association was stronger in women never using menopausal hormone therapy (HT) compared with past and current users (P-interaction < 0.0001). Our findings strongly suggest a protective effect for post-menopausal breast cancer through a better vitamin D supply as characterized by serum 25(OH)D measurement, with a stronger inverse association in women with low serum 25(OH)D concentrations (< 50 nM).