There is a lot in the news about the benefits of Vitamin D lately.
I have read the the level that most cancer patients should be at is above 50 in their blood.
http://www.johnshopkinshealthalerts.com/alerts/prostate_disorders/JohnsHopkinsProstateDisordersHealthalert_3424-1.html?ET=johnshopkins_blog:e39904:232271a:&st=email&st=email&s=EPH_100624_005
You might find interesting some of the things on the Vitamin D councils web page:
http://www.vitamindcouncil.org/