Sunshine (a natural source of vitamin D) and supplemental vitamin D appear to be really, really good for you.
This today in the Los Angeles Times:
Vitamin supplements have been both heralded and hyped over the years, only to ultimately fall from grace once research proves them to be little more than placebos in our quest for longer life or better health. But at least one substance may have true merit — vitamin D. Long considered just a supplement consumed with calcium for bone health, this humble vitamin may have untapped potential in fighting or preventing disease, suggests an explosion of new research. Not only has it shown promise in reducing the risk of, among other things, diabetes, pancreatic cancer, breast cancer and cardiovascular disease, but it also seems to improve infertility, weight control and memory.
How much supplemental vitamin D should you be taking? The Los Angeles Times reports a range of recommendations, with an upper daily limit of 2000 IU:
In November, 18 University of California researchers issued a statement saying 2,000 IU is appropriate for most people.
The full Los Angeles Times article can be read here.
Prometheus Unbound 
Some good points raised in that post. Will be back to check for more.
Cheers