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Seit die Norweger (wie andere Nord- und Mitteleuropäer) in den 1960er-Jahren Gefallen an Ferien an südlichen Stränden gefunden haben, ist die Rate der Melanomerkrankungen um den Faktor sechs gestiegen (nach 1990 gab es infolge der verbesserten Früherkennung jedoch einen Rückgang), wie Richard Setlow vom Brookhaven National Laboratory in Upton im US-Bundesstaat New York berichtet. Setlow hatte in den 1990er-Jahren als erster die krebsauslösende Wirkung von UV-Strahlen experimentell belegt.

Neben Hautkrebserkrankungen sind noch auch eine Reihe innerer Erkrankungen mit der Sonneneinstrahlung assoziiert: Karzinome in Darm, Lunge, Prostata oder der Brust sind in Australien weniger häufiger als in Norwegen, was einzig über die Produktion von Vitamin D in der Haut erklärt werden kann. Laut Setlow gibt es jedoch Zweifel an der Kausalität dieser Beziehung. Ungeklärt ist auch, warum die Prognose einiger Krebserkrankungen sich mit zunehmender Polnähe verbessert. Setlow vertritt in seiner Publikation die Ansicht, dass UV-Licht überwiegend günstige Wirkungen auf Krebserkrankungen haben. © rme/aerzteblatt.de

Anticancer Res. 2009 Sep;29(9):3501-9.Solar radiation, vitamin D and cancer incidence and mortality in Norway.
Moan J, Dahlback A, Lagunova Z, Cicarma E, Porojnicu AC.

Department of Radiation Biology, Rikshospitalet-Radiumhospitalet HF, Oslo, Norway.AbstractSolar radiation is of fundamental importance for human development and health: On the one hand, too much of it can lead to skin ageing and skin cancer, whilst on the other, too little of it can result in vitamin D deficiency, and, thereby lead to high incidence and poor prognosis of internal cancer as well as a number of other diseases. The following data, mostly from Norway, will be reviewed: Variation of ambient solar ultraviolet radiation (UV) and vitamin D status with season and latitude, variation of incidence rates and prognosis of skin cancer and variation of prognosis of internal cancer with latitude and season. In short, the following issues are discussed:

1) Vitamin D level varies with season, but probably not with latitude in Norway, because of an increased intake of vitamin D in the north; 2) Skin cancer incidence rates increase from north to south, as do annual fluence rates of UV radiation, while there seems to be a slight improvement in prognosis from north to south; 3) Prognosis of internal cancer is best for cases diagnosed in the seasons with the best vitamin D status, i.e. in summer and autumn; 4) Incidence rates of cutaneous melanomas have increased from 1960 to 1990, but have decreased slightly thereafter for young people; 5) Changes in sun exposure habits have taken place; 6) An increase in body mass index (BMI) of the population has occurred, which may have led to a worsening of the vitamin D status.
Proc Natl Acad Sci U S A. 2008 Jan 15;105(2):668-73. Epub 2008 Jan 7.Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure.

Moan J, Porojnicu AC, Dahlback A, Setlow RB.

Department of Radiation Biology, Institute for Cancer Research, Montebello, 0310 Oslo, Norway. johan.moan@fys.uio.noAbstractSolar 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 north-south 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.