Taking vitamin D supplements may slow or reverse the progression of low-grade prostate tumors. In a new study, many of the men who received vitamin D supplements demonstrated improved outcomes while the men who received a placebo either experienced no change to their tumors or their tumors got worse. Researcher Dr. Bruce Hollis comments, “We don’t know yet whether vitamin D treats or prevents prostate cancer. At the minimum, what it may do is keep lower-grade prostate cancers from going ballistic.” American Chemical Society, March 2015