As global knowledge of how human skin interacts with light increases, there has been a greater focus on the biochemical processes that occur in the human body following exposure to light, in particular the creation of a necessary vitamin: vitamin D
The vitamin D debate is complex and contentious, especially whether intentionally increasing UV exposure delivers health benefits that outweigh the known increased risk of skin cancer, and likely melanoma associated with heightened UV exposure.
Vitamin D is a pro-hormone (precursor to a hormone) that is known to have numerous actions and beneficial effects in the human body: from bone strength and development through support of the immune system, inflammatory response, prevention of age related diseases and, potentially, 17 different types of cancer. Virtually every organ in the human body has a receptor for this vitamin, indicating a need for a certain amount for healthy function.
Deficiency in vitamin D has been implicated in many diseases, including rickets, depression and even solid internal cancers. At present, however, epidemiological studies have only suggested an association between vitamin D deficiency and cancer: the causal relationship is yet to be demonstrated through clinical trials.
While it is possible to increase vitamin D levels through supplements or including particular foods in the diet, the most efficient source is exposure of skin to UV radiation. UV radiation, particularly UVB (270-300nm), is crucial to the production of the vitamin as it causes a molecule (7-dehydrocholestorol) that is common within the epidermis to develop into cholecalciferol, or vitamin D3. Research to date indicates that all vitamin D production, within humans, animals and even plants, requires UV radiation to catalyse the process. Even the vitamin D received from eating oily fish is only present as the fish consume ocean algae which produce vitamin D in UV drenched shallow waters. But the full range of effect from increased vitamin D is yet to be understood and much research only raises further questions.
For example, between the 1960’s and 90’s global incidence of skin cancer increased alongside an increase in UV radiation globally. The increase in skin cancer indicates that people were being exposed to more of exactly the type of radiation that produces vitamin D. Given the supposed internal cancer preventing properties of vitamin D it should follow that internal cancer rates dropped through these decades and that an inverse relationship between UV-Vitamin D levels and internal cancer incidence became apparent. In actual fact the opposite was true. While not increasing as quickly as skin cancer, the incidence of internal cancer rose consistently. There are also contradictions apparent when examining cancer incidence, mortality and geographic (latitudinal) location among Caucasian populations.
Caucasian populations at varying distances from the equator demonstrate interesting trends that both clarify and confuse the argument. Those living close to the equator experience an increase in UV exposure, skin cancer incidence and vitamin D levels, but also show increased incidence of internal cancers. A further intriguing trend is that those closer to the equator also have an improved prognosis in terms of mortality from internal and skin cancers. Research has shown that survival prognosis following cancer treatment improves if the patient is recovering during a period of high UV radiation, suggesting that vitamin D plays a significant role in recovery, but the high incidence of internal cancers in high UV regions turns the cancer prevention potential of vitamin D on its head.
Until detailed studies are carried out and the actions of vitamin D better understood in terms of cancer prevention and healthy body function individuals must proceed with a sense of balance, precaution and awareness.
The production of vitamin D can be improved by decreasing sugar and fat intake and increasing exercise, none of which have a known cancer risk increase associated with them. Likewise, increasing the amount of vitamin D in diets by including more oily fish and other foods is a safe and measurable way to increase vitamin D that carries no known health risk.
As The American Academy of Dermatology outlines in their Position Statement on vitamin D; an adequate amount of vitamin D should be obtained from a healthy diet that includes foods naturally rich in vitamin D, foods/beverages fortified with vitamin D, and/or vitamin D supplements. Vitamin D should not be obtained from unprotected exposure to ultraviolet (UV) radiation.
References:
http://www.aad.org/Forms/Policies/Uploads/PS/PS-Vitamin%20D.pdf
http://www.aad.org/annual_report/2008/science_research_vitaminD.html
http://www.ncbi.nlm.nih.gov/pubmed/18180454
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