Vitamin D-binding protein and vitamin D status of black Americans and white Americans

N Engl J Med. 2013 Nov 21;369(21):1991-2000. doi: 10.1056/NEJMoa1306357.

Abstract

Background: Low levels of total 25-hydroxyvitamin D are common among black Americans. Vitamin D-binding protein has not been considered in the assessment of vitamin D deficiency.

Methods: In the Healthy Aging in Neighborhoods of Diversity across the Life Span cohort of blacks and whites (2085 participants), we measured levels of total 25-hydroxyvitamin D, vitamin D-binding protein, and parathyroid hormone as well as bone mineral density (BMD). We genotyped study participants for two common polymorphisms in the vitamin D-binding protein gene (rs7041 and rs4588). We estimated levels of bioavailable 25-hydroxyvitamin D in homozygous participants.

Results: Mean (±SE) levels of both total 25-hydroxyvitamin D and vitamin D-binding protein were lower in blacks than in whites (total 25-hydroxyvitamin D, 15.6±0.2 ng per milliliter vs. 25.8±0.4 ng per milliliter, P<0.001; vitamin D-binding protein, 168±3 μg per milliliter vs. 337±5 μg per milliliter, P<0.001). Genetic polymorphisms independently appeared to explain 79.4% and 9.9% of the variation in levels of vitamin D-binding protein and total 25-hydroxyvitamin D, respectively. BMD was higher in blacks than in whites (1.05±0.01 g per square centimeter vs. 0.94±0.01 g per square centimeter, P<0.001). Levels of parathyroid hormone increased with decreasing levels of total or bioavailable 25-hydroxyvitamin D (P<0.001 for both relationships), yet within each quintile of parathyroid hormone concentration, blacks had significantly lower levels of total 25-hydroxyvitamin D than whites. Among homozygous participants, blacks and whites had similar levels of bioavailable 25-hydroxyvitamin D overall (2.9±0.1 ng per milliliter and 3.1±0.1 ng per milliliter, respectively; P=0.71) and within quintiles of parathyroid hormone concentration.

Conclusions: Community-dwelling black Americans, as compared with whites, had low levels of total 25-hydroxyvitamin D and vitamin D-binding protein, resulting in similar concentrations of estimated bioavailable 25-hydroxyvitamin D. Racial differences in the prevalence of common genetic polymorphisms provide a likely explanation for this observation. (Funded by the National Institute on Aging and others.).

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • African Americans* / genetics
  • Biological Availability
  • Bone Density
  • Cross-Sectional Studies
  • European Continental Ancestry Group* / genetics
  • Female
  • Genotype
  • Health Surveys
  • Homozygote
  • Humans
  • Male
  • Middle Aged
  • Parathyroid Hormone / blood*
  • Polymorphism, Genetic
  • United States
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D / pharmacokinetics
  • Vitamin D-Binding Protein / blood*
  • Vitamin D-Binding Protein / genetics

Substances

  • Parathyroid Hormone
  • Vitamin D-Binding Protein
  • Vitamin D
  • 25-hydroxyvitamin D