Free 25-Hydroxyvitamin D: Impact of Vitamin D Binding Protein Assays on Racial-Genotypic Associations
Research output: Contribution to journal › Article
Colleges, School and Institutes
- UNIVERSITY OF CALIFORNIA LOS ANGELES
- Pacific NW Natl Lab
- University of Colorado
- Portland VA Med Ctr
- KU Leuven Univ
- MRC Human Nutrition Research
- University of Pittsburgh
- Oregon Health & Science University
CONTEXT: Total 25-hydroxyvitamin D (25OHD) is a marker of vitamin D status and is lower in African Americans than in whites. Whether this difference holds for free 25OHOD (f25OHD) is unclear, considering reported genetic-racial differences in vitamin D binding protein (DBP) used to calculate f25OHD.
OBJECTIVES: Our objective was to assess racial-geographic differences in f25OHD and to understand inconsistencies in racial associations with DBP and calculated f25OHD.
DESIGN: This study used a cross-sectional design.
SETTING: The general community in the United States, United Kingdom, and The Gambia were included in this study.
PARTICIPANTS: Men in Osteoporotic Fractures in Men and Medical Research Council studies (N = 1057) were included.
EXPOSURES: Total 25OHD concentration, race, and DBP (GC) genotype exposures were included.
OUTCOME MEASURES: Directly measured f25OHD, DBP assessed by proteomics, monoclonal and polyclonal immunoassays, and calculated f25OHD were the outcome measures.
RESULTS: Total 25OHD correlated strongly with directly measured f25OHD (Spearman r = 0.84). Measured by monoclonal assay, mean DBP in African-ancestry subjects was approximately 50% lower than in whites, whereas DBP measured by polyclonal DBP antibodies or proteomic methods was not lower in African-ancestry. Calculated f25OHD (using polyclonal DBP assays) correlated strongly with directly measured f25OHD (r = 0.80-0.83). Free 25OHD, measured or calculated from polyclonal DBP assays, reflected total 25OHD concentration irrespective of race and was lower in African Americans than in US whites.
CONCLUSIONS: Previously reported racial differences in DBP concentration are likely from monoclonal assay bias, as there was no racial difference in DBP concentration by other methods. This confirms the poor vitamin D status of many African-Americans and the utility of total 25OHD in assessing vitamin D in the general population.
|Number of pages||9|
|Journal||Journal of Clinical Endocrinology and Metabolism|
|Early online date||23 Mar 2016|
|Publication status||Published - May 2016|
- Adult, African Continental Ancestry Group, Aged, Cross-Sectional Studies, European Continental Ancestry Group, Humans, Male, Vitamin D, Vitamin D-Binding Protein, Journal Article