Total and Free Circulating Vitamin D and Vitamin D-Binding Protein in Relation to Colorectal Cancer Risk in a Prospective Study of African Americans

Abstract

Background: Previous studies rarely evaluated the associations between vitamin D-binding protein and free vitamin D with colorectal cancer risk. We assessed these biomarkers and total 25-hydroxyvitamin D in relation to colorectal cancer risk in a sample of African Americans.Methods: Cases comprised 224 African American participants of the Southern Community Cohort Study diagnosed with incident colorectal cancer. Controls (N = 440) were selected through incidence density sampling and matched to cases on age, sex, and race. Conditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI) for associations between biomarker levels and colorectal cancer risk.Results: Vitamin D was inversely associated with colorectal cancer risk where the OR per-SD increase in total and free 25-hydroxyvitamin D were 0.82 (95% CI, 0.66-1.02) and 0.82 (95% CI, 0.66-1.01), respectively. Associations were most apparent among cases diagnosed >3 years after blood draw: ORs for the highest tertile versus the lowest were 0.69 (95% CI, 0.21-0.93) for total 25-hydroxyvitamin D and 0.71 (95% CI, 0.53-0.97) for free 25-hydroxyvitamin D. Inverse associations were seen in strata defined by sex, BMI, and anatomic site, although not all findings were statistically significant. Vitamin D-binding protein was not associated with colorectal cancer risk.Conclusions: Our findings suggest that total and free 25-hydroxyvitamin D may be inversely associated with colorectal cancer risk among African Americans.Impact: These findings highlight a potential role for vitamin D in colorectal cancer prevention in African Americans. Cancer Epidemiol Biomarkers Prev; 26(8); 1242-7. ©2017 AACR.

Figure 1. Associations between free vitamin D and colorectal cancer risk by selected participant characteristics

Odds ratios are presented as a per standard deviation increase in level of free vitamin D and result from conditional logistic regression models where cases and controls are matched on race, age, and sex. Odds ratios and 95% confidence intervals are adjusted for calendar week of sample collection, body mass index, education, smoking, physical activity, alcohol intake, history of colorectal cancer screening, and family history of colorectal cancer. Analyses include African American controls and cases with greater than 3 years between blood draw and diagnosis. Free vitamin D is calculated as 25(OH)D:VDBP molar ratio (x10³) and is a proxy for free 25-hydroxyvitamin D status. OR=odds ratio; CI=confidence interval. ^a P-values for interaction were calculated by inclusion of cross-product terms for free vitamin D and the variable of interest. We were unable to calculate a P-value for interaction between sex and free vitamin D status because sex was used as a matching factor.