Demographic, lifestyle, and genetic determinants of circulating concentrations of 25-hydroxyvitamin D and vitamin D-binding protein in African American and European American women.
Level 4 - case-series / case-control
Cross-sectional comparative study using healthy control cohorts
PubMed 28424184 · doi:10.3945/ajcn.116.143248
What was done
Plasma 25-hydroxyvitamin D [25(OH)D] and vitamin D-binding protein (VDBP) concentrations were compared between 909 African American (AA) and 847 European American (EA) healthy female control participants from two cohort studies (Carolina Breast Cancer Study and Women's Circle of Health Study). Demographic and lifestyle determinants of these biomarkers were evaluated across both groups, and 67 vitamin D-related genes were genotyped in AA women.
What was found
AA women had lower plasma 25(OH)D concentrations than EA women (mean ± SD: 14.2 ± 8.1 vs. 21.1 ± 11.5 ng/mL; P < 0.0001), while VDBP concentrations were similar (344 ± 133 vs. 336 ± 124 μg/mL; P = 0.25). Adjusting for VDBP and other covariates did not attenuate the racial difference in 25(OH)D. Demographic and lifestyle determinants of 25(OH)D were similar between groups. European GWAS-identified variants for 25(OH)D were not significant in AA women (P > 0.05), but AA carriers of the lactase-persistence variant rs4988235 had higher dietary vitamin D intake and higher 25(OH)D concentrations.
Why it matters
Because VDBP levels were similar between groups, the lower total 25(OH)D in African American women reflects lower free 25(OH)D rather than altered carrier protein binding. It also shows that genetic predictors of vitamin D status established in European cohorts do not readily translate to African American populations.
Limits
The cross-sectional design cannot establish causality. Genotyping was performed only in AA women, preventing direct genetic comparisons across racial groups. The sample was restricted to healthy female controls from breast cancer studies, limiting generalizability to men or other populations. Free 25(OH)D was inferred rather than directly measured.
Cited by
- supports African American women with a lactase gene single nucleotide polymorphism conferring lactose tolerance have significantly higher vitamin D levels.