Vitamin D status and cancer incidence, mortality, and prognosis

Vitamin D may play a role in cancer incidence, mortality, and prognosis. Several approaches have been used to investigate these associations, including using sun exposure as a proxy for vitamin D status, assessing vitamin D intake from food and supplements, directly measuring circulating 25(OH)D concentration, randomized controlled studies, and genetic studies including Mendelian randomization studies. There is mounting evidence from observational studies, Mendelian randomization studies, and some randomized studies that adequate vitamin D status may reduce cancer mortality, for multiple cancers. Some data suggest that individuals with levels below 50nmol/L are most likely to benefit from additional vitamin D. For cancer incidence, the evidence of an association with vitamin D deficiency is strongest for colorectal cancer and possibly ovarian cancer, but the results are not definitive. Important questions remain about the dose-response relationship, the levels required for the optimal benefit, the relevant timing of exposure, whether tumor characteristics or lifestyle factors may modify the association, and the effectiveness of supplemental vitamin D or vitamin D analogs as adjuvant therapy options.