From Harvard Public Health Review:

While vitamin D?s role in strengthening bones is well established, its links to cancer and immune-system malfunctions have only recently emerged. At the Harvard School of Public Health, nutrition experts say large segments of the population don?t get enough vitamin D and are urging the U.S. Food and Drug Administration to raise the daily recommended dose, from 400 international units to 800. For an update on what?s known so far about this important nutrient, the Harvard Public Health Review spoke with HSPH Professor of Nutrition and Epidemiology Edward Giovannucci.

Q: What are the documented benefits of vitamin D?

A: Vitamin D?s best-known role is in building strong bones. We?ve seen plenty of advertising urging people to take calcium to strengthen bones, but people also need to know that calcium can?t do the job well if they?re low on vitamin D. The two micronutrients work

More under the link below,

http://www.hsph.harvard.edu/review/spring07/spr07vitaminD.html