Vitamin D helps prevent some cancers.
Vitamin D deficiency is associated with an increased risk of breast, colon, prostate, pancreatic and ovarian cancer. Researchers think vitamin D might have antiproliferative effects in these cancers.
Recent research seems to support this hypothesis. Higher vitamin D serum levels seem to be associated with a reduced risk of cancer and cancer-related mortality in men. And people with higher intakes of vitamin D appear to have a lower risk for pancreatic cancer.
Explain to patients that this is interesting research, but it's too soon to say that taking vitamin D supplements will prevent cancer. But it's another good reason to ensure that they get enough vitamin D through dietary measures and sun exposure.