The Epidemiology of Vitamin D and Cancer Risk

The relation between vitamin D status and cancer risk has been investigated in a number of epidemiologic studies, while data from interventional studies remain scarce. The approaches to estimate vitamin D status have been varied, and include direct measures of circulating 25(OH)vitamin D (25(OH)D) levels, surrogates, or determinants of 25(OH)D, including region of residence, intake, and sun exposure estimates. In terms of cancer sites, the body of evidence is the most extensive for colorectal cancer, for which support comes from studies of 25(OH)D, vitamin D intake, multiple predictors of 25(OH)D, and region of residence in a sunny climate. The evidence for breast cancer is also intriguing, but prospective studies of 25(OH)D are sparse and somewhat conflicting. In one case–control study, retrospectively reported sun exposure during ages 10–19 was most strongly associated with reduced risk of breast cancer. For prostate cancer, the data on circulating 25(OH)D have been equivocal, suggesting no association or a weak inverse association, but studies tend to support a benefit of sun exposure on prostate cancer risk. It is plausible that for prostate cancer, exposure to vitamin D level much longer before the time of diagnosis is the most relevant. Most of the epidemiologic studies to date have examined vitamin D status in relation to risk of cancer, but emerging evidence suggests that vitamin D may be an important factor for cancer progression and mortality, independently of any effects on incidence. Further study is needed to establish the precise role of vitamin D on carcinogenesis, especially in terms of when in the lifespan and on what stages of carcinogenesis vitamin D is relevant, the precise intakes and levels required, the magnitude of the association, and which cancer sites are most affected.