The National Institutes of Health recommend 600 International Units (IU) of vitamin D per day. One cup of vitamin D-fortified milk provides 100 units, while 3 ounces of oil-based tuna provides another 200 units. But is it wise to soak up UV rays to get vitamin D? The debate is so hot that the Skin Cancer Foundation has called it The D Dilemma.

According to Dr. Barbara Gilchrest, chief dermatologist at Boston University's medical school, the harmful effects of sunlight far outweigh the benefits of vitamin D production. The Skin Cancer Foundation and other cancer organizations agree, but paradoxically, the National Cancer Institute is investigating whether vitamin D may play a role in preventing or treating cancer.

However, other health experts take issue with such contentions, noting that the skin manufactures vitamin D in response to UV light. One of them is Michael Holick, author of The UV Advantage and a researcher at Boston University, who estimates that 30 to 60 percent of adults are vitamin D deficient.

Holick maintains you can get a sizeable chunk of that daily vitamin D requirement in natural sunlight. He advocates that people with average skin tones spend five to 10 minutes in the sun, two to three times per week, from spring to fall, without sunscreen. People with lighter skin should spend less time, and people with darker skin should spend more time, he adds.

Still, the sun's dangers are undeniable: Ultraviolet (UV) radiation contributes to excessive aging of the skin and more than 1 million skin cancers each year in the United States, including melanoma, the deadliest form of any cancer. "Any individual or organization that advocates intentional sun exposure as the preferred means of producing vitamin D is doing a tremendous disservice to the public," Gilchrest says.

"While some researchers and professional groups are now questioning whether higher vitamin D levels should be recommended for optimal health, no responsible group or individual is advocating UV exposure as a remedy, Gilchrest adds. This should put to rest these erroneous claims that sunlight is good medicine."

Along these lines, dermatologists and other cancer experts suggest that people limit their time out in the sun. If you must be in the sun, they recommend using a broad-spectrum sunscreen that protects against both UVB and UVA rays and has a sun protection factor (SPF) of at least 15. Still, they note that sunscreen can lure some people into a false sense of protection, so it's best to avoid the sun completely, especially during midday, when UV rays are at their strongest.