Serum vitamin D concentrations are non-linearly related to breast cancer risk in postmenopausal women
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Background: Post-menopausal women are at high risk for breast cancer. The association between serum 25-hydroxyvitamin D [25(OH)D] concentration and breast cancer in post-menopausal women is not well understood. Objectives: The aim of this study was to investigate the association between serum 25(OH)D and breast cancer using nationally representative sample surveys. Methodology: In this cross-sectional study, we used seven cycles of National Health and Nutrition Examination Surveys from 2001 through 2014. Participants were non-institutionalized post-menopausal women (n=8100). Logistic regression was performed to determine the association between serum 25(OH)D concentrations and breast cancer prevalence. A restricted cubic spline method was used to assess the non-linear association. Results: The prevalence of breast cancer was 3.3%, 4.0%, 4.6%, 6.4%, and 6.9% in the groups with serum 25(OH)D levels of <30, 30-<50, 50-<75, 75-<100, and ?100 nmol/L, respectively. The risk of having breast cancer was significantly higher in the serum 25(OH)D 75-<100 nmol/L category compared to the 25(OH)D <30 nmol/L concentration [OR and 95% CI; 2.21 (1.23-3.98)]. Furthermore, a significant non-linear relationship between serum 25(OH)D concentrations (when used as a continuous variable) and breast cancer in all post-menopausal women (p for non-linear trend 0.032) was observed. Overall, the risk of breast cancer was highest (OR=1.5) between 70 nmol/L and 80 nmol/L of serum 25(OH)D concentration in all post-menopausal women. Conclusion: An adverse association was observed between serum 25(OH)D concentration and breast cancer in post-menopausal women. Further research is needed to elucidate the mechanism of vitamin D in cancer pathogenesis.