Balancing the effects of UV radiation from sunlight

Considering the dangers of UV exposure to skin, supplementation of vitamin D is the safer method of supply, a new US study says.

In the review, current findings on how ultraviolet radiation (UVR) from sunlight can lead to the development of skin cancer (melanoma) were analyzed (1). It is generally accepted that UVR is a major risk factor for melanoma skin cancer development depending on the host, the body site, the dose, and timing of UVR exposure. The most skin damage has been shown to be due to UV-B radiation, although there is important evidence demonstrating that UV-A is also capable of skin damage. Despite this, the incidence of melanoma continues to rise because of the ongoing epidemic of outdoor sun-seeking behavior as well as indoor tanning.

The development of melanoma is multifactorial with discrete genetic pathways and environmental factors contributing. UVR through unprotected sun exposure is a major environmental risk factor that leads to melanoma development through direct and indirect DNA damage, and through immune modulation, via inflammation and immunosuppression.

One of the positive effects of UV exposure to the skin is that it synthesizes pre-vitamin D, which is then converted by the liver and kidney to active form of vitamin D (1,25[OH2] vitamin D). Vitamin D is essential for human health, with its best understood role involving calcium and bone metabolism but may also contribute to health in other contexts, including cancer and immunity. The wavelength of UVR needed for pre-vitamin D synthesis by human skin falls within the UV-B spectrum, which, unfortunately, is also responsible for major skin damage, including cancer development.

The scientists commented that although complete understanding of these effects is not yet clear, it is important to consider the known dangers of UV exposure to skin, when balancing potential benefits of UV for vitamin D production. This would be particularly important because oral supplementation of vitamin D is widely available and inexpensive, they said. Moreover, oral supplements probably offer a more precise and predictable means of correcting low vitamin D levels, since UV exposure is highly variable and depends on factors such as quantity of skin exposed, intensity of UV, and degree of skin pigmentation, the scientists concluded.

1. Garibyan L. and Fisher D. E. How Sunlight Causes Melanoma. Curr Oncol Rep. 2010.