Association between Plasma 25-Hydroxyvitamin D and Breast Cancer Risk: A Matched Case-Control Study

Background: The protective role of vitamin D in the occurrence of breast cancer is nowadays a controversial matter. Based on conflicting results of the studies in this field and also considering the prevalence of vitamin D deficiency in Iranian women, this work was conducted to evaluate the association between vitamin D and breast cancer. Method: This matched case-control study was conducted on 70 newly diagnosed breast cancer patients and 70 controls with the same age, menopause status, and time of blood sampling in Zanjan. Information regarding demographic, reproductive, history of diseases, medication, use of dairy products, and sunlight exposure was collected using a questionnaire. The serum level of vitamin D was measured with ELISA method. The data were analyzed utilizing chi-square test, independent t-test, and odds ratios using conditional logistic regression model. Results: The mean level of vitamin D was 39.04 and 63.34 ng/ml in the cases and controls, respectively (P=0.046). The proportion of the cases in the highest quartile of vitamin D was significantly smaller than that in the controls compared with the lowest quartile (Ptrend=0.028). Using conditional logistic regression model, an inverse and independent association was observed between vitamin D and breast cancer after controlling main confounders. The risk of breast cancer was independently associated with body mass index and low income. Conclusion: In this study, an inverse association was confirmed between vitamin D and breast cancer. Prospective intervention studies should be performed to explore its role in the prevention of breast cancer.