Abstract 1279: Association between vitamin D levels and colorectal cancer in African Americans
Authors: Siddiqi Sariya , Pibiri Fabio , Xicola Rosa Munoz , Kittles Rick A. , Llor Xavier , Kupfer Sonia S. , Ellis Nathan A. 
Published: May 2015

Abstract
Background. Colorectal cancer (CRC) is the fourth most commonly diagnosed cancer in the world and there is a sizeable disparity in CRC incidence and mortality between African Americans (AAs) and all other US racial groups that remains unexplained. Associations between vitamin D levels and CRC have been widely reported in many populations, but there are few studies in AAs. We hypothesized that vitamin D levels are lower in AAs with CRC. Methods. 401 subjects were prospectively ascertained in endoscopy clinics in the Illinois Medical District: 130 healthy controls, 136 individuals with adenomatous polyps, and 130 individuals with CRC; 270 of 401 subjects were AA. Clinical data included age, gender, and BMI (kg/m2); smoking and drinking status; anti-inflammatory medication use; education and income levels; physical exercise level. Levels of serum 25-(OH) vitamin D2 and D3 were measured by Quest Diagnostics using liquid chromatography and tandem mass spectroscopy. Thirty nine potentially functional SNPs from eight vitamin D-related genes (CYP2R1, CYP24A1, CYP27A1, CYP27B1, CYP3A4, DHCR7, GC, and VDR) were genotyped using the Sequenom MassARRAY platform. We tested associations between vitamin D and CRC using logistic regression models, adjusting for age, gender, and time of year of blood collection, and we tested each clinical covariate in the model. In addition, we tested associations between SNPs and vitamin D levels using logistic regression, adjusting for age, gender, and time of collection. Results. Levels of total vitamin D (D2 + D3) and of vitamin D3 were statistically significantly lower in AAs compared to Non-Hispanic Whites (NHW). Approximately 15% of AAs exhibited detectable levels of vitamin D2, which was evidence of supplementation; only 8% of NHWs supplemented. Supplementation was significantly associated with older ages, female gender, less alcohol use and less exercise. Vitamin D3 levels were 22% lower in AA CRC cases compared to AA controls (18.5 ng/ml vs 23.7 ng/ml; P &lt;0.03); vitamin D3 levels were not significantly different in NHW CRC cases compared to controls (29.8 ng/ml vs. 28.2 ng/ml). Vitamin D3 levels in adenoma cases were not significantly different compared to controls in either group (23.5 ng/ml in AA adenoma cases and 27.3 ng/ml in NHW adenoma cases). The SNP rs1544410 in VDR and rs3829251 in DHCR7 had the smallest p values (0.008 and 0.013, respectively). The minor allele of rs16847024 in GC was associated with lower vitamin D3 levels; this same SNP was associated with left-sided CRC in AAs in a larger case-control study performed by our group. rs3829251 in DHCR7 has been previously associated with serum vitamin D levels in Han Chinese. Conclusion. These data demonstrated that vitamin D levels are associated with protection against CRC in AAs. SNPs in vitamin D-related genes may modulate vitamin D levels and risk of CRC.
Citation Format: Sariya Siddiqi, Fabio Pibiri, Rosa Munoz Xicola, Rick A. Kittles, Xavier Llor, Sonia S. Kupfer, Nathan A. Ellis. Association between vitamin D levels and colorectal cancer in African Americans. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1279. doi:10.1158/1538-7445.AM2014-1279