Epidemiological Evidence for Vitamin D and Colorectal Cancer

Since Garland and Garland formulated the hypothesis that vitamin D may protect against colorectal cancer in 1980, various epidemiological approaches have been undertaken to evaluate this hypothesis. These approaches include studies based on regional solar UVB radiation, plasma‐ or serum‐based studies, dietary studies, and those examining multiple factors that influence vitamin D status. Studies over the past several decades have tended to support that higher levels of vitamin D may decrease risk of colorectal cancer. An important implication is that current recommended dietary intakes such as 200–400 IU/d may be too low to exert appreciable benefits. To substantially reduce risk, higher levels of vitamin D associated with sunshine exposure or considerably higher intakes may be required. Recent studies also suggest a potential benefit of vitamin D on other digestive system cancers. One study suggested that a better vitamin D status at the time of diagnosis and treatment, as indicated by season of diagnosis, may improve survival from colorectal cancer. Darker‐skinned individuals who tend to make less vitamin D may be at particularly high risk for digestive system cancer. The strong biological evidence for a protective role of vitamin D supports the epidemiological data. More study is needed to determine the optimal levels and intakes of this vitamin to optimally reduce colorectal cancer risk.