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Solar radiation is the main cause of skin cancers. However, it also is a main source of vitamin D for humans. Because the optimal status of vitamin D protects against internal cancers and a number of other diseases, a controversy exists: Will increased sun exposure lead to net health benefits or risks? We calculated the relative yield of vitamin D photosynthesis as a function of latitude with a radiative transfer model and cylinder geometry for the human skin surface. The annual yield of vitamin D is 3.4 and 4.8 times larger below the equator than in the U.K. and Scandinavia, respectively. In populations with similar skin types, there are clear latitude gradients of all major forms of skin cancer, indicating a northsouth gradient in real sun exposure. Surprisingly, the incidence rates of major internal cancers also increase from north to south. However, the survival prognosis also improves significantly from north to south. Reasons for these findings are discussed in view of the role of vitamin D. In Norway, melanoma rates increased by a factor of 6 from 1960 to 1990, while the prognosis improved in the same period. After 1990, melanoma rates have remained constant or even decreased in age groups <50 years, whereas the prognosis has not improved further. These data, together with those for internal cancers and the beneficial effects of an optimal vitamin D status, indicate that increased sun exposure may lead to improved cancer prognosis and, possibly, give more positive than adverse health effects.body mass index ͉ cutaneous malignant melanoma ͉ squamous cell carcinoma ͉ ultraviolet radiation T here is a controversy as to whether increased sun exposure to Western populations would prolong or shorten lifetime expectancy, result in fewer or more cancer deaths, and, in general, lead to health benefits or risks (1, 2). For years, emphasis has been placed on the increasing time trends of incidence and mortality rates of cutaneous malignant melanoma (CMM) (3, 4) and, in contrast, on the protective role of vitamin D regarding many types of internal cancer and other diseases (5-7). Too much sun exposure has been blamed for the high and increasing incidence rates of CMM. However, solar radiation is a major, if not the main, source of vitamin D in humans. Therefore, a population's increased sun exposure leads to improved vitamin D status. The observation that the incidence and mortality of several types of internal cancers decreases with decreasing latitude in the United States and other countries initiated the research on vitamin D-cancer relationships in the 1980s and 1990s. However, in some cases, there is an inverse gradient of the rates of internal cancer with latitude (1), with the rates being higher in regions with high annual UV fluences (New Zealand and Australia) than in countries with low annual UV fluences (Northern Europe, Scandinavia, and the U.K.), despite the fact that the populations of these regions are closely related genetically or, at least, have similar skin types, which is important for the photosy...

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Vitamin D has important benefits in reducing the risk of many conditions and diseases. Those diseases for which the benefits are well supported and that have large economic effects include many types of cancer, cardiovascular diseases, diabetes mellitus, several bacterial and viral infections, and autoimmune diseases such as multiple sclerosis. Europeans generally have low serum 25-hydroxyvitamin D [25(OH)D] levels owing to the high latitudes, largely indoor living, low natural dietary sources of vitamin D such as cold-water ocean fish, and lack of effective vitamin D fortification of food in most countries. Vitamin D dose-disease response relations were estimated from observational studies and randomized controlled trials. The reduction in direct plus indirect economic burden of disease was based on increasing the mean serum 25(OH)D level to 40 ng/mL, which could be achieved by a daily intake of 2000-3000 IU of vitamin D. For 2007, the reduction is estimated at euro187,000 million/year. The estimated cost of 2000-3000 IU of vitamin D3/day along with ancillary costs such as education and testing might be about euro10,000 million/year. Sources of vitamin D could include a combination of food fortification, supplements, and natural and artificial UVB irradiation, if properly acquired. Additional randomized controlled trials are warranted to evaluate the benefits and risks of vitamin D supplementation. However, steps to increase serum 25(OH)D levels can be implemented now based on what is already known.

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Essential features of the epidemiology and photobiology of cutaneous malignant melanoma (CMM) in Norway were studied in comparison with data from countries at lower latitudes. Arguments for and against a relationship between ultraviolet radiation (UV) from sun and sun beds are discussed. Our data indicate that UV is a carcinogen for CMM and that intermittent exposures are notably melanomagenic. This hypothesis was supported both by latitude gradients, by time trends and by changing patterns of tumor density on different body localizations. However, even though UV radiation generates CMM, it may also have a protective action and/or an action that improves prognosis. The same may be true for a number of internal cancers. There appears to be no, or even an inverse latitude gradient for CMM arising on non-UV exposed body localizations (uveal melanoma). Furthermore, CMM prognosis was gradually improved over all years of increasing incidence (up to 1990), but during the last 10 to 15 years, incidence rates decreased and prognosis was not further improved. While CMM incidence rates are twice as high in South Norway as in North Norway, the ratios of death rates to incidence rates are higher in the North, where the annual UV fluences are lower. Death- and incidence rates in Australia and New Zealand fully support this. Comparisons of skin cancer data from Norway and Australia/New Zealand indicate that squamous cell carcinoma and basal cell carcinoma are mainly related to annual solar UVB fluences, while UVA fluences play a larger role for CMM.

Background: A variety of studies have shown beneficial effects of different types of phototherapy in skin disorders. Such therapy leads to enhanced cutaneous vitamin D synthesis, which may be one of the mechanisms of action. Furthermore, another nutrient, folate, can probably also be influenced by UV radiation.

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