From
msnbc.com:
For the past few years
vitamin D has been the "it" vitamin, with studies wildly trumpeting the supplement's role in strengthening bones, reducing the risk of some cancers, heart disease, along with fighting autoimmune diseases and diabetes. But long-awaited new dietary guidelines say there's no proof that megadoses of the "sunshine vitamin" prevent cancer, diabetes or other conditions.
While some people will need a bit more vitamin D than they're already getting, some studies suggest that too much could actually cause some kinds of cancer, according to the panel of experts at the prestigious Institute of Medicine, the health arm of the National Academy of Sciences.
A National Cancer Institute study last summer was the latest to report no cancer protection from vitamin D and the possibility of an increased risk of pancreatic cancer in people with the very highest D levels. Super-high doses — above 10,000 IUs a day — are known to cause kidney damage.