Vitamin D and Sunlight: Strategies for Cancer Prevention and Other Health Benefits

Vitamin D and Sunlight: Strategies for Cancer Prevention and Other Health Benefits
Vitamin D deficiency is a worldwide health problem. The major source of vitamin D for most humans is sensible sun exposure. Factors that influence cutaneous vitamin D production include sunscreen use, skin pigmentation, time of day, season of the year, latitude, and aging. Serum 25-hydroxyvitamin D [25(OH)D] is the measure for vitamin D status. A total of 100 IU of vitamin D raises blood level of 25(OH)D by 1 ng/ml. Thus, children and adults who do not receive adequate vitamin D from sun exposure need at least 1000 IU/d vitamin D. Lack of sun exposure and vitamin D deficiency have been linked to many serious chronic diseases, including autoimmune diseases, infectious diseases, cardiovascular disease, and deadly cancers. It is estimated that there is a 30 to 50% reduction in risk for developing colorectal, breast, and prostate cancer by either increasing vitamin D intake to least 1000 IU/d vitamin D or increasing sun exposure to raise blood levels of 25(OH)D >30 ng/ml. Most tissues in the body have a vitamin D receptor. The active form of vitamin D, 1,25-dihydroxyvitamin D, is made in many different tissues, including colon, prostate, and breast. It is believed that the local production of 1,25(OH)2D may be responsible for the anticancer benefit of vitamin D. Recent studies suggested that women who are vitamin D deficient have a 253% increased risk for developing colorectal cancer, and women who ingested 1500 mg/d calcium and 1100 IU/d vitamin D3 for 4 yr reduced risk for developing cancer by >60%.
Vitamin D is likely to be one of the oldest hormones. It has existed for at least 750 million years, when phytoplankton synthesized it in response to sunlight (1). Throughout evolution, vitamin D played a critical role in the evolution of vertebrates as they left their high-calcium ocean environment for the calcium-deficient terra firma. Nocturnal rodents and other rodent-like species that lived underground needed little, if any, vitamin D to survive. It has been speculated that when the asteroid hit the earth 65 million yr ago, one of the survival characteristics for nocturnal mammals was that they did not require sunlight-mediated vitamin D synthesis to survive, unlike the dinosaurs. Dinosaurs likely depended on the sun to satisfy their vitamin D requirement to utilize dietary calcium efficiently for the maintenance of their massive skeletons (1). Thus, the lack of sunlight-mediated vitamin D synthesis after the asteroid impact may have been related to the demise of the dinosaurs.
The industrialization of Europe and the United States in the 17th through the 19th centuries gave birth to the devastating bone-deforming and growth-retarding disease rickets. Although Sniadecki in 1822 suggested that children who were living in the industrialized cities in Poland were at a higher risk for rickets than children who were living in rural areas as a result of lack of sun exposure, it would take 100 yr before it was reported that exposure to ultraviolet radiation from a mercury arc lamp or sun exposure prevented and cured rickets (2,3). The association of sun exposure and latitude with cancer mortality was first noted by Hoffman in 1915 (4). He reported mortality from cancer in cities at various latitudes and observed a gradient decline in the death rate. Peller and Stephenson (5) recognized that people who were exposed to enough sunlight to induce nonlethal, nonmelanoma skin cancers had a decreased incidence of more malignant tumors. They observed that the rate of skin cancer in US Navy personnel was eight times higher, whereas the total number of deaths from other cancers was reduced by >60% in comparison with the civilian population. This was followed by Apperley (6), who reported that people who live at higher latitudes in the United States, including New Hampshire, Vermont, and Massachusetts, were more likely to die of cancer than adults who live in southern states, such as Alabama and Georgia.
In the 1980s to 1990s, Garland et al. (7) and Gorham et al. (8) completed a number of epidemiologic studies and noted that there was a strong negative correlation between latitude, sun exposure, and poor vitamin D status and the risk for developing many deadly cancers, including colon, breast, ovarian, and melanoma (Figure 1). These observations were followed by Grant (9), who noted that several cancers were reduced by adequate exposure to solar ultraviolet B radiation. He estimated that during a span of 24 yr, 1970 through 1994, a total of 566,400 Americans died prematurely from 13 cancers as a result of inadequate sun exposure. This was confirmed by a more recent analysis that concluded that between 50,000 and 63,000 Americans and 19,000 and 25,000 adults who live in the United Kingdom die prematurely from cancer each year