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Serum Vitamin D Status and Breast Cancer Risk by Receptor Status: A Systematic Review

ABSTRACT Background: The association between vitamin D status and breast cancer risk is equivocal. No systematic reviews or meta-analyses have examined this association stratified by receptor status. Our objective is to conduct a systematic review to answer the question, “Is there a relationship between lower serum/plasma vitamin D levels and increased risk of triple negative breast cancer (TNBC) specifically?” Methods: We systematically searched Embase and PubMed databases for published original research studies examining the risk of a breast cancer diagnosis according to vitamin D status. We excluded studies that did not provide risk estimates stratified by receptor status. Results: Fourteen studies met our criteria, including case-control, nested case-control, and case-series studies, reflecting the cumulative results of 13,135 breast cancer cases. When grouped by relevancy to TNBC, the proportion of analyses across all study types showing a significant association between vitamin D status and breast cancer diagnosis was 37% for non-TNBC analyses, 48% for analyses that included some TNBC cases, and 88% for TNBC analyses. Conclusions: Our results suggest that low vitamin D status may particularly increase the risk of TNBC, although more research is needed to determine if this association is causative. Women should be routinely screened for 25(OH)D deficiency.