Sunlight, Skin Cancer, and Vitamin D

Abstract

Both in the public and in the scientific community, there is an ongoing debate about the relevance of beneficial and adverse effects of UV exposure. There is no doubt that solar UV exposure is the most important environmental risk factor for the development of non-melanoma skin cancer. Consequently, sun protection has been advocated as a key principle of skin cancer prevention campaigns. However, 90% of all vitamin D needed by the human body has to be formed in the skin through the action of the sun – a serious conflict, for an association of vitamin D deficiency and multiple independent diseases including various types of cancer, bone diseases, autoimmune diseases, infectious diseases, hypertension, and cardiovascular disease has now been convincingly demonstrated in epidemiologic and laboratory studies. An important link that advanced our understanding of these new findings was the discovery that the biologically active vitamin D metabolite 1,25-dihydroxyvitamin D [1,25(OH)2 D] is not exclusively produced in the kidney, but in many other tissues including prostate, colon, skin, breast, and osteoblasts. Extrarenally produced 1,25(OH)2D is now considered to represent an autocrine or paracrine hormone that regulates various cellular functions including cell growth. A paradigm shift occurred with the discovery that plasma levels of 25-hydroxyvitamin D [25(OH)D, calcidiol] are physiologically important for the extrarenal production of 1,25(OH)2D. It is now evident that 25(OH)D plasma levels represent a more accurate measure of the vitamin D status of an individual than the more tightly regulated plasma levels of 1,25(OH)2D. This development has revitalized the field of vitamin D research and led to the conclusion that the minimally desired 25(OH)D plasma levels should rise from 30 to 75 nmol/l. We and others have demonstrated that strict sun protection causes vitamin D deficiency in risk groups. In the context of new scientific findings that convincingly demonstrate an association of vitamin D deficiency with a variety of severe diseases including various types of cancer, the detection and treatment of vitamin D deficiency in sun-deprived risk groups is very important. It should be accentuated that vitamin D status should be monitored in groups that are at high risk of developing vitamin D deficiency (e.g., nursing-home residents or patients under immunosuppressive therapy). Vitamin D deficiency should be treated, e.g., by giving vitamin D orally. Dermatologists and other clinicians have to recognize that there is convincing evidence that the protective effect of less intense solar UV radiation outweighs its mutagenic effects. Although further work is necessary to define an adequate vitamin D status and adequate guidelines for solar UV exposure, it is at present mandatory that public health campaigns and recommendations of dermatologists on sun protection consider these facts. Well-balanced recommendations on sun protection have to ensure an adequate vitamin D status, thereby protecting us against adverse effects of strict sun protection without significantly increasing the risk to develop UV-induced skin cancer.