A new study published this month finds that the hormonally active form of vitamin D, Calcitriol 1,25-dihydroxyvitamin D(3), inhibits the growth of many kinds of cancerous cells, including breast cancer, indicating that vitamin D3 can be useful in treating and even preventing a variety of cancers.
Authors of the study said that caner cell growth is inhibited by "anticancer actions including cell cycle arrest, promotion of apoptosis and inhibition of invasion, metastasis, and angiogenesis." Vitamin D's anti-inflammatory properties and interference with estrogen synthesis further explains its anti-tumor properties.
Two studies from 2007 used meta-analysis, which combines data from multiple reports, to find that therapeutic doses of vitamin D could prevent up to half of all cases of breast cancer, and two-thirds of all cases of colorectal cancer in the United States. The studies showed a direct correlation between blood levels of vitamin D and cancer. Those with the highest blood levels were found to be at the lowest risk, and the lowest blood levels at the highest risk.