Blood Vitamin D Levels in Relation to Genetic Estimation of African Ancestry

Background: African-Americans generally have lower circulating levels of 25 hydroxyvitamin D [25(OH) D] than Whites, attributed to skin pigmentation and dietary habits. Little is known about the genetic determinants of 25(OH) D levels nor whether the degree of African ancestry associates with circulating 25(OH) D. Methods: With the use of a panel of 276 ancestry informative genetic markers, we estimated African and European admixture for a sample of 758 African-American and non-Hispanic White Southern Community Cohort Study participants. For African-Americans, cut points of <85%, 85% to 95%, and >= 95% defined low, medium, and high African ancestry, respectively. We estimated the association between African ancestry and 25(OH) D and also explored whether vitamin D exposure (sunlight, diet) had varying effects on 25(OH) D levels dependent on ancestry level. Results: The mean serum 25(OH) D levels among Whites and among African-Americans of low, medium, and high African ancestry were 27.2, 19.5, 18.3, and 16.5 ng/mL, respectively. Serum 25(OH) D was estimated to decrease by 1.0 to 1.1 ng/mL per 10% increase in African ancestry. The effect of high vitamin D exposure from sunlight and diet was 46% lower among African-Americans with high African ancestry than among those with low/medium ancestry. Conclusions: We found novel evidence that the level of African ancestry may play a role in clinical vitamin D status. Impact: This is the first study to describe how 25(OH) D levels vary in relation to genetic estimation of African ancestry. Further study is warranted to replicate these findings and uncover the potential pathways involved. Cancer Epidemiol Biomarkers Prev; 19(9); 2325-31. (C) 2010 AACR.