Introduction
The Greek hero Daedalus, according to ancient mythology, built his son Icarus wings to escape a Labyrinthian imprisonment. Escape he did, but despite his father's stern warnings, Icarus flew too close to the sun. The wings melted, and the boy plunged to his death in the sea below.
Today, the sun's rays continue to evoke warnings, especially from medical and public health professionals: wear the appropriate sunscreen and protective clothing, limit exposure time, seek shade. The reason? The sun's ultraviolet (UV) radiation, in the form of UVA (longer wavelength) and UVB (shorter wavelength) rays, has been implicated in skin aging and skin cancers, particularly skin cancers like basal-cell and squamous-cell carcinomas and melanoma. But scientists have also found that UV radiation is not all bad. It stimulates vitamin D production in the skin, and there is some still-controversial evidence of a possible connection to reduced risk of colon and rectal cancer incidence and death from breast cancer.
The challenge for scientists supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) is to understand as much as they can about both positive and negative effects of UV radiation. What they learn should result in major public health and prevention implications for skin conditions.
These studies lend support to the dominant theory that UV exposure is the main identifiable andSeveral recent NIAMS-supported studies have focused on the interaction of UV radiation, skin cancer, and vitamin D. preventable cause of skin cancer, and emphasize the importance of UV-induced vitamin D in cell growth and differentiation.
- A study by NIAMS-supported researcher Dr. Robert Stern and his colleagues at Harvard University (JNCI 1998;90(17):1278-1284) has looked at the incidence of squamous- and basal-cell carcinoma in patients with the skin disease psoriasis who had participated some 20 years ago in a trial of PUVA therapy, a treatment using UVA and a chemical, psoralen, that sensitizes skin to UV radiation. The scientists found that even in those patients with minimal PUVA or UVB exposure over the past decade, their initial exposure to high-dose PUVA in the trial continued to result in new squamous- and basal-cell cancers. This, say the investigators, shows that PUVA actually began the cancer process rather than simply stimulating a cancer that had already started. A similar study of melanoma incidence in the same population showed that PUVA can initiate this form of skin cancer.
- To learn how UV radiation could start and promote skin cancers, NIAMS grantee Dr. Alice Pentland at the University of Rochester (N.Y.) examined prostaglandins, cell components that contribute to tissue inflammation. Focusing on the protein COX-2, which helps generate prostaglandins, the study (Carcinogenesis 1998;19(5):723-729) showed that 1) skin-reddening doses of UVB increased levels of COX-2, and 2) skin areas with squamous-cell carcinoma had higher levels of COX-2 than normal, non-sun-exposed skin of the same patients. This UVB-induced increase in COX-2 could be a potential target for drug therapy in preventing skin tumors.
- Vitamin D, which is synthesized in the skin as a result of UV exposure, promotes normal growth and differentiation of skin structures, which is somehow disrupted in cancers of the skin. With support from NIAMS, Drs. Zhongjian Xie and Daniel Bikle at the University of California San Francisco found that squamous-cell carcinoma cells failed to differentiate like normal skin cells in response to vitamin D (J Invest Dermatol 1998;110(5):730-733). Their investigations suggest that these cancerous cells lack a substance in their genetic machinery that allows vitamin D to do its developmental work.
Despite the success of these studies, the effects of UV radiation still need to be better understood to guide prevention efforts against skin damage. That is why NIAMS recently cosponsored a major Research Workshop on the Risks and Benefits of Exposure to Ultraviolet Radiation and Tanning. The September 1998 workshop featured experts from government, academia and industry who reviewed the state of the science on UVA and UVB radiation, and addressed the health effects of various tanning methods and sunscreens.
Unlike the mythical Icarus, NIAMS intends to pursue the sun's rays from a safe distance. What it finds on its scientific journey should yield significant benefits to millions of people.
Be Sun-Safe!
- Use a sunscreen with a sun protection factor (SPF) of 15 or more that blocks both UVB and UBA radiation.
- Wear protective clothing: long sleeves, pants, and wide-brimmed hats.
- Limit your hours in the sun, especially during peak sunlight hours (between 10 a.m. and 3 p.m.) and during the summer, when the sun is stronger.
- Take advantage of "structured shade": trees, pavilions, and other outdoor structures that afford protection from the sun's rays.
Major Workshop Sharpens Focus on UV Radiation, Tanning
Much more research is needed on the both the harmful and beneficial effects of UV light to improve the basis for public health actions, concluded participants at the Sept. 16-18 Research Workshop on the Risks and Benefits of Exposure to Ultraviolet Radiation and Tanning. A combination of time-of-day adjustments for outdoor activities, structured shade, clothing and other physical blockers, and sunscreens are needed "to allow prudent people to enjoy the benefits of outdoor activities while minimizing the risks."
The workshop, cosponsored by NIAMS and five other federal agencies, involved basic and clinical researchers, the medical community, and representatives from government, industry and the public. Presentations and discussions covered five major topics: sources and measurement of UV radiation, UV effects on the skin, beneficial effects of UV, ways to produce and enhance the tanning process, and sunburn as an indicator of future biological events.
The other workshop sponsors were the National Cancer Institute, the National Institute of Environmental Health Sciences, the National Institute on Aging, the Centers for Disease Control and Prevention, and the Food and Drug Administration.
The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), a part of the National Institutes of Health (NIH), leads the Federal medical research effort in arthritis and musculoskeletal and skin diseases. The NIAMS supports research and research training throughout the United States, as well as on the NIH campus in Bethesda, MD, and disseminates health and research information. The National Arthritis and Musculoskeletal and Skin Diseases Information Clearinghouse (NAMSIC) is a public service sponsored by the NIAMS that provides health information and information sources. Additional information can be found on the NIAMS Web site at http://www.niams.nih.gov/.