Solar radiation, vitamin D and cancer incidence and mortality in Norway.

Solar 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.