Review of Recent Advances in Understanding the Role of Vitamin D in Reducing Cancer Risk: Breast, Colorectal, Prostate, and Overall Cancer

This article is a narrative review of recent epidemiological findings regarding ultraviolet-B (UVB) dose or exposure, serum 25- hydroxyvitamin D [25(OH)D] concentrations, vitamin D supplementation, and genetic variations in 25(OH)D concentration for incidence, survival, and mortality rates of overall and breast, colorectal, and prostate cancer. According to ecological studies, solar UVB doses are inversely correlated with incidence/mortality rates for about 20 cancer types. Observational studies support a role of higher 25(OH)D concentrations in reducing risk of breast and colorectal cancer incidence and mortality rates but, for prostate cancer, in increasing incidence rates while reducing mortality rates. Mendelian randomization studies offer little support for vitamin D in reducing cancer risk. Their primary limitation is that they only investigate small variations in genetically predicted 25(OH)D concentration near the population mean value. The secondary analyses from the VITAL clinical trial indicated significant reductions from 2000 IU/d of vitamin D3 supplementation in all-cancer incidence and mortality rates for selected subgroups. Thus, Hill's criteria for causality in a biological system are now largely satisfied for supporting the claim that vitamin D reduces the risk of cancer incidence and death.