title: A critical review of studies on vitamin D in relation to colorectal cancer.
abstract: Vitamin D intake has been hypothesized to reduce the risk of several types of cancer. Vitamin D and its analogues have demonstrated anticancer activity in vitro and in animal models. However, the risk of colorectal cancer in relation to dietary vitamin D remains controversial. A literature search was performed for articles on epidemiologic studies of vitamin D and colorectal cancer and the mechanisms involved. Studies that combine multiple sources of vitamin D or examine serum 25(OH)D3 usually find that above-average vitamin D intake and serum metabolite concentrations are associated with significantly reduced incidence of colorectal cancer. A number of mechanisms have been identified through which vitamin D may reduce the risk of colorectal and several other types of cancer. Although studies that include vitamin D from all sources or serum 25(OH)D3 usually show significantly reduced incidence of colorectal cancer in association with vitamin D, analyses limited to dietary vitamin D tend to have mixed results. The likely reason that dietary vitamin D is not a significant risk reduction factor for colorectal cancer in many studies is that dietary sources provide only a portion of total vitamin D, with supplements and synthesis of vitamin D in the skin in association with solar UV-B radiation providing the balance. There is strong evidence from several different lines of investigation supporting the hypothesis that vitamin D may reduce the risk of colorectal cancer. Further study is required to elucidate the mechanisms and develop guidelines for optimal vitamin D sources and serum levels of vitamin D metabolites.
authors.affiliation: SUNARC, San Francisco, CA 94109, USA. wbgrant@infionline.net
authors.forename: William B
authors.initials: WB
authors.lastname: Grant
authors.forename: Cedric F
authors.initials: CF
authors.lastname: Garland
mesh_terms: D016588:Anticarcinogenic Agents / Q000008:administration & dosage*; D002136:Calcium, Dietary / Q000008:administration & dosage; D016022:Case-Control Studies; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D019587:Dietary Supplements; D006801:Humans; D015994:Incidence; D012307:Risk Factors; D014466:Ultraviolet Rays; D014807:Vitamin D / Q000008:administration & dosage* / Q000097:blood
chemical_list: D016588:Anticarcinogenic Agents; D002136:Calcium, Dietary; D014807:Vitamin D