Vitamin D status and cancer incidence and mortality.

The role of vitamin D in cancer incidence and mortality has been investigated using several approaches, including using sun exposure as a proxy for vitamin D status, assessing vitamin D intake from food and supplements, using a predicted score to estimate vitamin D status, and directly measuring circulating 25(OH)D. A variety of complementary study designs have been implemented with various strengths and limitations. Although definitive randomized control trial data are lacking, there is strong evidence for a protective relationship of vitamin D and colorectal cancer incidence. Evidence for other cancers is not as consistent. More recently, large pooling projects have begun to investigate rarer cancers, studies have investigated common variation and expression of vitamin D-related genes and their relationships to cancer, and evidence has emerged on the role of vitamin D in cancer survival. Further study is needed to answer important questions that remain about the most affected cancer sites, the timing of vitamin D exposure in relation cancer etiology duringthe life span (e.g., adolescence or adulthood), the dose-response/optimal levels required for the most benefit, and which stages of carcinogenesis (e.g., incidence or progression) are most relevant.