Vitamin D baseline levels at diagnosis of breast cancer: A systematic review and meta-analysis

Vitamin D is a steroid hormone that exerts its actions through ligation of the vitamin D receptor (VDR), a transcription factor of the nuclear receptor family. VDR has not only physiologic actions in calcium metabolism but also several other cellular effects through extensive binding to the DNA and modification of genome expression. In cancer, it has neoplasia-suppressive effects and various mechanisms of action mediating cancer cell inhibition have been described. Vitamin D deficiency has been linked to increased risk of breast cancer. A role of the vitamin once the disease has been diagnosed is also probable.