I'm reading The Vitamin D Solution by Michael Holick. I'm sure the relationship between vitamin D and cancer has been discussed previously on these boards. This book examines the relationship in detail. It's well written, well-do***ented, and is written by someone with 30 years of research experience in the field - he is not just out to make a quick buck on a diet fad.
• Most American's suffer from a deficiency of vitamin D, principally from not enough exposure to the sun. (In the last 20-30 years, Americans have developed a phobia to sun exposure.)
• This can be remedied through reasonable amount of unprotected (no sunscreen) exposure to sunlight, better diets, and if needed, dietary supplements of calcium and Vitamin D.
• The benefits can include reduced risk for cancer as well as better overall physical and mental health.
* The best way to increase vitamin D levels is sun exposure. However, depending on your job, where you live, your race, and your age, getting enough vitamin D from the sun can be difficult - this is where supplements have a role. For instance, I teach school in Connecticut, and from September to May, I don't get to spend as much time in the sun as I need and would like.
Anyway, I suggest you check it out for yourself if you're interested.