Abstract B34: Total and free vitamin D, vitamin D binding protein, and colorectal cancer risk in the Southern Community Cohort Study
Authors: Andersen Shaneda Warren , Shu Xiao-Ou , Cai Qiuyin , Steinwandel Mark , Blot William J. , Zheng Wei 
Published: March 2017

Abstract
Purpose: Animal and cell line studies provide biologic plausibility that circulating vitamin D may reduce colorectal cancer risk. However, studies in humans have been inconclusive, and few have considered the role of vitamin D binding protein and free vitamin D. We comprehensively evaluated whether vitamin D biomarkers predict risk of colorectal cancer by measuring circulating level of vitamin D binding protein, and total and free 25-hydroxyvitamin D in pre-diagnostic blood serum samples. We used data from a nested case-control study that includes a large number of African Americans, who typically have lower levels of total vitamin D than those of European descent, and who have been understudied in previous investigations.
Methods: Participants of the nested case-control study were drawn from the Southern Community Cohort Study, a prospective cohort study primarily comprised of low-income white and African Americans. Participants aged 40-79 were enrolled into the study from 2002 to 2009, and provided information on lifestyle factors and demographics. Cases were participants who were diagnosed with an incident colorectal cancer after study enrollment and donated a blood sample for the study. Controls were selected through incidence density sampling of the cohort members who had donated a blood sample and were free of any cancer except skin cancer at the time of the case's diagnosis. Controls were individually matched to cases by age at diagnosis, sex, and race at a ratio of two controls for each case. A total of 298 cases and 580 controls were included in the current study. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between vitamin D biomarker levels and colorectal cancer risk.
Results: ORs for the associations between total and free 25-hydroxyvitamin D with colorectal cancer risk indicated inverse associations, although all confidence intervals crossed unity. More apparent associations were observed among cases with greater than three years between blood draw and diagnosis. Among these subjects, the adjusted ORs for the comparison between participants in the highest tertile of free 25-hydroxyvitamin D levels compared to those in the lowest tertile were 0.65 (95%CI: 0.38,1.11) for all subjects and 0.46 (95%CI: 0.25,0.84) for African Americans. In participants with greater than three years between blood draw and diagnosis, the inverse association pattern was seen in all strata defined by sex, body mass index, and anatomic site, although not all analyses reached significance at P ≤ 0.05. Small samples size in analyses restricted to whites resulted in unstable estimates. Vitamin D binding protein was not associated with colorectal cancer risk.
Conclusions: In our study, total and free 25-hydroxyvitamin D are inversely associated with colorectal cancer risk, particularly in African Americans, suggesting a potential role of vitamin D in colorectal cancer prevention.
Citation Format: Shaneda Warren Andersen, Xiao-Ou Shu, Qiuyin Cai, Mark Steinwandel, William J. Blot, Wei Zheng. Total and free vitamin D, vitamin D binding protein, and colorectal cancer risk in the Southern Community Cohort Study. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr B34.