Sunlight, Vitamin D and Malignant Melanoma

Abstract

Solar radiation represents an essential requirement for life, not only by spending the thermal energy for photosynthesis in plants, which provides our atmosphere with oxygen, but also by facilitating the cutaneous synthesis of vitamin D in vertebrates and many other organisms. It is well known that humans and most vertebrates have to obtain an adequate source of vitamin D, in order to develop and maintain a healthy mineralized skeleton and in order to be protected against cancer and a broad variety of other diseases. On the other hand, solar UV radiation can be assumed to be the most relevant environmental carcinogen causing melanoma and nonmelanoma skin cancer with increasing incidences. During the last decades, epidemiological studies and experimental animal models, including genetically engineered mice, the Xiphophorus hybrid fish, the south american oppossum and human skin xenografts, have further elucidated the multi-step process of UV-induced melanomagenesis. It has to be emphasized that, in contrast to intermittent, short-term high-dose solar UV-exposure, more chronic less intense exposure (which is recommended by many experts in the fleld to obtain a sufficient vitamin D status) has not been found to be a risk factor for the development of melanoma and in fact has been found in several studies to be protective. Interestingly, several independent lines of investigation have demonstrated convincing evidence that vitamin D and/or analogs may be effective in the prevention and treatment of melanoma. This essay summarizes our present understanding about the pathogenic role of UV radiation and of vitamin D for malignant melanoma.