Vitamin D, Sun Exposure Reduce Prostate Cancer Risk
The combination of greater lifetime exposure to sunlight and “protective” genes decreases the risk of prostate cancer by up to 54%, reports a study in Cancer Research (2005;65:5470–9).
This year, more than 230,000 American men will be diagnosed with prostate cancer. Men over the age of 50 and those who have a first-degree relative with prostate cancer are more likely to develop the disease. Several dietary factors have also been associated with an increased risk, including high intake of red meat and animal fat. Fruit and vegetable consumption appears to lower the risk. In particular, lycopene, a red pigment found in high concentrations in tomato products, may confer protection.
Vitamin D deficiency may also be related to an increased risk of prostate cancer, and vitamin D, which inhibits the spread of cancer and renders cancer cells less invasive, has been shown to interfere with the disease’s progression.
Most of the vitamin D in the body is derived from exposure of the skin to ultraviolet light from the sun. Ultraviolet light causes the skin to convert a compound similar to cholesterol into an inactive form of vitamin D, which is then further metabolized by the liver and kidneys into the active form of the vitamin. It is of interest to note that the prostate is also able to accomplish the final step in the conversion of vitamin D into its active form.
Prostate cells contain specialized receptors for vitamin D. Variations in the gene that produces vitamin D receptors may be associated with prostate cancer risk. Although several studies have reported an association between sun exposure and decreased risk, few have explored the combined effects of sun exposure and variations in the vitamin D receptor gene on prostate cancer risk.
The new study compared 450 non-Hispanic white men with advanced prostate cancer with 455 men without the disease. (Advanced cancer was defined as that which has spread beyond the capsule surrounding the prostate into the adjacent tissue or lymph nodes, or cancer that has metastasized to distant sites.) Total lifetime sun exposure was assessed by inquiring about time spent outdoors in recreational and occupational activities, evaluating the amount of exposure by geographical region of residence, and by means of a “sun exposure index.” The sun exposure index was determined by comparing the skin colors of sun exposed and unexposed areas of the body, which provided an estimate of cumulative lifetime sun exposure. Blood or tissue samples were taken from the participants and analyzed for variations in the vitamin D receptor gene.
Sun exposure was expressed in terms of three categories (tertiles) and five categories (quintiles), ranging from the lowest to the highest amount of exposure. The risk of prostate cancer was 50% less among men in the highest quintile of the sun exposure index compared with those in the lowest quintile. Similarly, men in the highest quintile of occupational sun exposure had significantly lower rates of the disease than men with the lowest exposure. Several variations in the vitamin D receptor gene were associated with reductions in risk. Men in the highest tertile of sun exposure who had “protective” genes had a 54% reduction in risk compared with men in the lowest tertile who also had protective genes, suggesting that a combination of “protective” variants of the vitamin D receptor gene and high sun exposure seem to confer the most protection against prostate cancer.
These results support the findings of other studies suggesting a protective effect of sun exposure against prostate cancer development. Of course, the beneficial effects of sunlight must be balanced against the adverse effects of excessive sun exposure, particularly premature skin aging and skin cancers. One vitamin D researcher has suggested that adequate amounts of vitamin D can be synthesized by exposing the arms and legs or the hands, arms, and face to sunlight for 5 to 15 minutes, two to three times a week between 10 a.m. and 3 p.m. during the spring, summer, and autumn. For people concerned about the adverse effects of even small amounts of ultraviolet light, vitamin D can also be obtained from dietary supplements and vitamin D–enriched foods, although it is not known whether vitamin D supplements would provide the same protection as sunlight exposure.
Kimberly Beauchamp, ND, received her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She is a co-founder and practicing physician at South County Naturopaths, Inc., in Wakefield, RI. Dr. Beauchamp teaches holistic medicine classes and provides consultations focusing on detoxification and whole-foods nutrition.
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