gms | German Medical Science

Introduction: Numerous studies have suggested that vitamin D may reduce the risk of breast cancer. However, only few studies have assessed the association of breast cancer and serum 25-hydroxyvitamin D [25(OH)D], a medium-term biomarker of vitamin D supply. We therefore analyzed the association of serum 25(OH)D concentrations with the risk of postmenopausal breast cancer. Because estrogens are known to influence vitamin D metabolism we investigated effect modification by hormone therapy (HT).

Material and Methods: We used 1398 breast cancer cases and 1394 matched controls (age 50 to 74 years) from the Rhine-Neckar-Region of the population based, two centre case-control study MARIE (Mammary Carcinoma Risk Evaluation). Information on breast cancer risk factors was collected by a personal interview and data on lifetime HT using a pictogram of preparations. 25(OH)D concentration was measured in serum samples with an enzyme immunoassay. We used conditional logistic regression models with adjustment for potential confounders to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for breast cancer.

Results: Serum 25(OH)D concentration was significantly inversely associated with the risk of postmenopausal breast cancer. Compared with the lowest category (< 30 nM), the OR (95% CI) for the highest category of 25(OH)D (≥ 75 nM) was 0.32 (0.24, 0.43), (ptrend < .0001). The inverse association with increasing levels of 25(OH)D was stronger in women who never used menopausal hormone therapy than that in past and in current users, with ORs per 10 nM increment in 25(OH)D of 0.77 (0.72, 0.83), 0.87 (0.80, 0.95) and 0.96 (0.91, 1.02), respectively (p Interaction < .0001).

Conclusions: These results strongly support the hypothesis of a protective effect for postmenopausal breast cancer through a better vitamin D supply. In addition, this association may be modified by use of hormone therapy, the attenuation in current users being stronger than that in past users.