Treating prostate cancer cells with a vitamin D-like compound appears to make them more susceptible to the destructive effects of radiation. Of course drug companies are making drug analogs to use rather than vitamin D as they can't patent a natural vitamin and make a profit on it.
However, it couldn't be any clearer that vitamin D is essential for the prevention of not only prostate cancer but also breast cancer. That is why African Americans have higher incidences of both. Their dark skin limits UV-B from entering the skin and converting cholesterol to vitamin D.
What are other ways of treating prostate cancer? See the blog entry from Tuesday where I discussed those.
British Journal Cancer Aug 18, 2003;89(4):746-53