LAS VEGAS — It goes without saying that protection from excessive ultraviolet light throughout life is advocated by dermatologists to prevent skin cancer and photoaging, noted Dr. James M. Spencer.
“We dermatologists basically tell Americans, 'Use sunscreen or sunblock all the time.' That's our public health message, and it's been a consistent message for 20 years,” Dr. Spencer said at the annual meeting of the American Society of Cosmetic Dermatology and Aesthetic Surgery. “In animal and human studies, sunscreens have clearly proved to help prevent photoaging, lower the incidence of actinic keratoses, and lower the incidence of squamous cell carcinoma. That's beyond dispute.”
The American Academy of Dermatology recently issued a position statement recommending that “an adequate amount of vitamin D should be obtained from a healthy diet that includes food rich in vitamin D, foods/beverages fortified with vitamin D, and/or vitamin D supplements; it should not be obtained from unprotected ultraviolet (UV) radiation.”
The statement also pointed out that the current intake levels recommended by the Institute of Medicine, the health policy research arm of the National Academy of Sciences, “may be revised upward due to evolving research on the increasing clinical benefit of vitamin D.”
The wisdom of avoiding sun and using sunscreen has been questioned over the last few years, initially by epidemiologists who were looking to correlate human behavior with the development of melanoma, Dr. Spencer said. Then came a review article in 2007 by Dr. Michael F. Holick, an endocrinologist at Boston University, which estimated that 40%–60% of the adult population in the United States is vitamin D deficient (N. Engl. J. Med. 2007;357:266–81). The article calls for “sensible sun exposure” to ensure that adequate amounts of vitamin D are made in the skin, noting that exposure of the arms and legs for 5–30 minutes between 10 a.m. and 3 p.m. twice a week is “adequate” for most people.
“Some moderate sun exposure for both children and adults is appropriate,” Dr. Holick said in an interview. “Yes, you can always wear a broad-rimmed hat or some kind of sun protection for your face. It's the most sun damaged area; it's only about 9% of your body surface, and it doesn't provide you with that much of your vitamin D.”
According to the article, which was supported in part by grants from the National Institutes of Health and the UV Foundation, a key cause of vitamin D deficiency is sunscreen use, which “reduces vitamin D3 synthesis.” It also states that the ultraviolet B radiation emitted from tanning beds is a good source of vitamin D3 “when used in moderation.”
The importance of obtaining adequate levels of vitamin D is not in dispute, said Dr. Spencer of Mount Sinai School of Medicine, New York. Vitamin D has emerged as a candidate for the chemoprevention of a variety of malignancies and systemic diseases, including melanoma; breast, colon, and prostate cancer; multiple sclerosis; hypertension; cardiovascular disease; type 1 diabetes; Crohn's disease; schizophrenia; and depression.
However, there is no reason to believe that sun protection dangerously lowers vitamin D levels, said Dr. Spencer, who has a private dermatology practice in St. Petersburg, Fla. “Even if it did, the public has largely ignored our sun protection message, based on results of recent surveys of sun protection habits. It is a mistake to encourage the public to get intentional sun exposure for their health.”
He went on to note that vitamin D production in the skin “is highly variable by such factors as skin pigmentation and time of year, and therefore is not a reliable way to elevate vitamin D. It is unlikely that anyone goes to the beach or the tanning parlor to make more vitamin D, but this issue lets them rationalize that doing something they know is bad for them is actually okay. The people most at risk for vitamin D deficiency—dark-skinned nursing home residents—do not go to tanning salons.”
According to the Institute of Medicine guidelines, the recommended minimal daily intake of vitamin D is 200 IU for children and adults to age 50 years, 400 IU for adults aged 50–70 years, and 600 IU for adults older than 70 years.
The American Academy of Pediatrics Committee on Nutrition recently recommended increasing oral intake in children to 400 IU per day but does not recommend increased sun exposure because of skin cancer risk (Pediatrics 2008;122:1142–52).
In a pharmacokinetic study, a team of researchers that included Dr. Holick demonstrated that healthy men use up to 5,000 IU of vitamin D per day (Am. J. Clin. Nutr. 2003;77:204–10). This is “an order of magnitude higher than we thought we needed,” said Dr. Holick, professor of medicine, physiology, and biophysics at the university, and coauthor of the book, “The UV Advantage” (New York: Ibooks Inc., 2004). “We probably need to increase by 10-fold our vitamin intake to satisfy our body's requirement.”