Vitamin D status and colorectal cancer: Results from a systematic literature review

Background: In 2004, approximately 105,000 persons were diagnosed with colon cancer and 39,000 were diagnosed with rectal cancer (www.cdc.gov/cancer/index.htm). Some researchers have reported a protective role for vitamin D in colorectal cancer (CRC) etiology and/or prognosis and concluded that public health action is needed to increase the recommended daily intake. Methods: We conducted a systematic literature review examining the association between vitamin D status and cancer; one of the subtypes of cancer recognized was CRC. The systematic literature review spanned from 1992 to 2007, and 33 relevant articles related to CRC were identified from the PubMed, EMBASE, ISI Citation, and CINAHL databases. Studies were peer-reviewed, published in English, conducted on a sample of human adults, and epidemiologic in nature. Results: Of 22 studies that examined the association of dietary and/or supplemental vitamin D intake and CRC, 10 found a protective effect. Four studies assessed sunlight exposure and CRC risk; all reported a protective effect. Of seven studies that measured the effect of vitamin D metabolites on CRC, four reported a protective effect. Approximately half of the studies on vitamin D status and CRC risk cited a significant protective effect on cancer etiology and/or prognosis. However, most of the studies possessed several methodological limitations, including failure to control for important confounders, recall bias, and the use of proxies to measure sun exposure. Conclusion: Based on our findings, we conclude that the evidence of the protective effect of vitamin D status and CRC etiology and/or prognosis is currently inconclusive.