U.S. National Cancer Institute researchers set out to see if vitamin D might protect against prostate cancer, the second most frequently diagnosed cancer in men worldwide. They tracked vitamin D concentrations in the blood of 749 men diagnosed with prostate cancer and 781 men who did not have the disease.
They found no association between higher levels of the vitamin and a reduced prostate cancer risk. The findings hinted at a possible increased risk for aggressive prostate cancer in men with higher blood concentration of vitamin D, but this link was not statistically significant, the researchers said.
This one study did not reveal any benefit from Vitamin D. There have been others that do show a benefit. This is why it is important to continue to do studies and use scientific method to assess things.
I ask patients to take a multivitamin a day, but not extra Vitamin D.