The health benefits of sunlight and the risk of skin cancer from UV exposure are still controversial. The literature was analyzed in terms of reviews, controlled and epidemiological studies for the relationships between sunshine exposure and overall cancer mortality, as well as mortality from cancer of the prostate, colon and breast. The residential and/or occupational sun exposure rate seemed to be positively correlated with a lower risk of overall morality due to organ cancer. A normal vitamin D status appeared to be an important precondition, via the local and autocrine synthesis of 1,25(OH)2D3 in the target tissues. The vitamin D hormone system is necessary for cell proliferation and differentiation; different types of vitamin D receptor gene polymorphism seemed to be associated with cancer cell growth. The health benefits of sunlight appear to outweigh the risk of skin cancer. However, the optimal UV exposure, the target level of circulating vitamin D, and whether vitamin D is the only pathway are still undetermined.

Current sun safety messages stress the importance of sun protection in avoiding the consequences of excessive exposure to ultraviolet radiation (UVR), such as skin cancers, cataracts and other eye diseases, and viral infections caused by UV-induced immunosuppression. However, adequate exposure to UVR has an important role in human health, primarily through UV-induced production of vitamin D, a hormone essential to bone health. Vitamin D insufficiency may be associated with increased risks of some cancers, autoimmune diseases and mental health disorders such as schizophrenia. Here, we review the evolution of current sun exposure practices and sun-safe messages and consider not only the benefits, but also the detrimental effects that such messages may have. UVR-induced vitamin D production can be inhibited by factors such as deep skin pigmentation, indoor lifestyles, older age, sun avoidance behaviours and clothing habits that limit skin exposure, with deleterious consequences for health. There is some early evidence that sun-safe messages are beginning to cause a decrease in skin cancer rates in young people. After the widespread promotion of sun safety, it may now be appropriate to refine public health messages to take better account of variations between groups and their susceptibility to the dangers and benefits of sun exposure.

By studying more than 1,200 patients with cutaneous melanoma and long-term follow-up, I examined the relationship between solar elastosis and age at diagnosis of melanoma, key features of melanoma, and the outcome of overall survival in melanoma. I found that melanomas with elastosis were diagnosed significantly later than those without elastosis (P approximately 0; log-rank test). This result may be because elastosis is positively related to age. However, I also found that melanomas of head and neck areas, which tend to have more elastosis, were diagnosed at later ages than melanomas of other body sites (P = 1.2 x 10-5; log-rank test). Thus, a second explanation for the results favors a protective effect of elastosis on the development of cutaneous melanoma, possibly related to increased levels of vitamin D. I also found that once melanoma develops, cases with elastosis demonstrated no differences in thickness, mitotic rate, ulceration, or overall survival time from cases without elastosis.