Equivalent anticancer activities of dietary vitamin D and calcitriol in an animal model of breast cancer: Importance of mammary CYP27B1 for treatment and prevention

▸ Dietary vitamin D3 and calcitriol exhibit equivalent tumor inhibition in mouse models of breast cancer. ▸ At moderate, achievable doses dietary vitamin D3 does not cause hypercalcemia, demonstrating safety. ▸ Tumor CYP27B1 and local calcitriol synthesis play a major role in the anticancer activity of vitamin D3. ▸ Endocrine activity of calcitriol derived from tumor and other extra-renal sources also contribute. ▸ Avoidance of vitamin D deficiency is important for reducing breast cancer risk.