High doses of Vitamin D won't help reduce a man's risk of prostate cancer. According to a new study conducted by researchers from the National Cancer Institute, men with more vitamin D in their blood are just as likely to develop the disease as men with less. In fact, men with a higher concentration of vitamin D in their blood are at a greater risk for the most aggressive form of the disease. While the finding wasn’t considered statistically significant, the investigators believe it might raise a red flag.