This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The observation of an ecologic correlation between solar radiation exposure and colon cancer risk has spawned a number of epidemiologic studies of the associations of dietary vitamin D intake, serum levels of vitamin D metabolites and more recently vitamin D receptor (VDR) gene variants and colon cancer. While a non-significant inverse association of dietary vitamin D intake and colon cancer risk was found in a number of prospective studies, analyses of plasma 25-hydroxyvitamin D (25(OH)D) concentrations, a biomarker for vitamin D, generally support an inverse association. Vitamin D receptor (VDR) gene variants have been variably associated with risk of colon cancer in epidemiologic studies. We sought to further clarify the relationship between colon cancer and three single-nucleotide polymorphisms (SNPs) in the VDR gene (Cdx-2, FokI and TaqI) in a population-based case-control study of 250 incident cases and 246 controls. Colon cancer cases were more frequently homozygous for the Cdx-2 A allele (9.2 versus 4.1%, P = 0.06). Cdx-2 AA homozygotes were at increased risk with an unadjusted odds ratio (OR) of 2.47 [95% confidence interval (CI): 1.13-5.37, P = 0.022];adjustment for age, sex, body mass index (BMI), non-steroidal anti-inflammatory use and family history of colorectal cancer yielded an OR of 2.27 (CI: 0.95-5.41, P = 0.065). Carriers of the FokI TT genotype were also at increased risk with an adjusted OR of 1.87 (CI: 1.03-3.38, P = 0.038). Haplotype analyses showed significant increased colon cancer risk for carriers of the Cdx-2-FokI A-T haplotype and the FokI-TaqI T-G haplotype. The three-SNP Cdx-2-FokI-TaqI (A-T-G) haplotype showed a similar association with an adjusted OR of 3.63 (CI: 1.01-13.07). A strong positive association was observed for the Cdx-2 variant among individuals with low BMI or low waist circumference. Our results suggest that genetic variation at the VDR locus, in particular Cdx-2 and FokI SNPs, may influence colon cancer risk and these associations may be modified by adiposity.
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