Exposure to sunlight can have significant effects on human endocrinology. In particular, vitamin D is synthesized via exposure of the skin to ultraviolet light, which in turn, becomes subsequently hydroxylated in the liver and kidney to its active form, 1,25-dihydroxy vitamin D. In 1990, Schwartz and Hulka published their hypothesis about vitamin D and prostate cancer.77 They rationalized that many of the known risk factors for prostate cancer could potentially be explained by vitamin D deficiency. Table 22.7 lists some of the risk factors associated with increased or decreased risk of prostate cancer and how these mechanistically could relate to Vitamin D.
Age is a well-accepted risk factor for prostate cancer. Data have shown that synthesis of vitamin D diminishes with advancing age.78 In addition, the elderly have less sun exposure, in part due to residence in homes for the aged. African American's are at highest risk for prostate cancer and tend towards a more aggressive disease phenotype.79 Although, numerous genetic, epigenetic and environmental hypotheses may explain this observation, melanin skin pigmentation can inhibit vitamin D synthesis.80 Asian's are relatively protected from prostate cancer development,81 in this population oily fish consumption is relatively high. Oily fish is the only known dietary source of vitamin D82 (prior to milk supplementation,
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