A new study suggests that the benefits of moderately increased exposure to sunlight – namely the production of vitamin D, which protects against the lethal effects of many forms of cancer and other diseases – may outweigh the risk of developing skin cancer in populations deficient in vitamin D.
Ultraviolet A (UVA) radiation and visible light are the primary causes of malignant melanoma, the deadliest form of skin cancer. But solar radiation is also a major, if not the main, source of vitamin D in humans. In the presence of sunlight, the body converts certain precursor chemicals to active vitamin D.
In the current study scientists used a model incorporating information on solar radiation intensity and a vertical cylinder shape to represent the human body’s skin surface to calculate the relative production of vitamin D via sunlight as a function of latitude, or distance from the equator. The cylindrical model more realistically represents human body sun exposure than flat surface exposure measurements used in previous models. The scientists also examined the incidence of and survival rates for various forms of cancer by latitude.
According to the calculations, people residing in Australia (just below the equator) produce 3.4 times more vitamin D as a result of sun exposure than people in the United Kingdom, and 4.8 times more than people in Scandinavia.
In populations with similar skin types, there is also a clear increase in the incidence of all forms of skin cancer from north to south.
The scientists also found that the incidence rates of major internal cancers such as colon cancer, lung cancer, and cancers of the breast and prostate also increased from north to south. However, when the scientists examined the survival rates for these cancers, they found that people from the southern latitudes were significantly less likely to die from these internal cancers than people in the north.
Melanoma is triggered by UVA (the long UV wavelengths) and visible light. Vitamin-D production in the body, on the other hand, is triggered by UVB (the short UV wavelengths at the earth’s surface).
Vitamin D is easily accessible in many foods and liquids, such as cod liver oil and milk, and in dietary supplements.