Vitamin D and Breast Cancer

Vitamin D regulates calcium and phosphorus blood levels and bone metabolism via effects on intestine, kidney, and bone. Vitamin D is formed from 7-dehydrocholesterol in the skin by ultraviolet irradiation or is taken up from dietary sources. Vitamin D must be metabolically altered successively in the liver and kidney to form the biologically most active compound, 1,25-dihydroxyvitamin D3. This active compound acts through binding to a specific receptor, the vitamin D receptor, which is a member of the steroid hormone receptor family. During the last fifteen years, it has become apparent that the active form of vitamin D exerts effects on a variety of tissues apparently unrelated to calcium homeostasis. 1,25-Dihydroxyvitamin D3 has been shown to promote cellular differentiation and inhibit proliferation of haematopoietic cells, cancer cells, and keratinocytes. In addition, studies with animal models for cancer have shown that 1,25-dihydroxyvitamin D3 administration can prolong the survival of leukaemic mice and suppress the growth of tumours of different origin, including breast, colon, skin, and lung. This thesis focuses on a possible role of vitamin D in the treatment of breast cancer.