Michael Holick, director of the vitamin D research laboratory at Boston University, infuriated the dermatology community in 2004 when he published "The UV Advantage," a book advocating limited unprotected sun exposure in addition to vitamin D supplements as the best way to combat the widespread deficiency he'd seen in his studies.

Despite losing his credentials in the Boston University Dermatology Department over his claims, he stands by his recommendation of 10 minutes of unprotected exposure on the arms and legs two or three times a week. He takes 1,400 IU (international units) of vitamin D per day, which is higher than the recommended 200 to 600 IU. While it is possible to take too much vitamin D, you would have to take more than 10,000 IU every day for months to cause a problem. The body destroys any excess vitamin D produced in the skin from sun exposure.