Journal
JOURNAL OF CLINICAL ENDOCRINOLOGY & METABOLISM
Volume 101, Issue 5, Pages 2226-2234Publisher
ENDOCRINE SOC
DOI: 10.1210/jc.2016-1104
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Funding
- National Institutes of Health (NIH)
- National Institute on Aging
- National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
- National Center for Advancing Translational Sciences
- NIH Roadmap for Medical Research [U01 AG027810, U01 AG042124, U01 AG042139, U01 AG042140, U01 AG042143, U01 AG042145, U01 AG042168, U01 AR066160, UL1 TR000128]
- Medical Research Council [U105960371, U123261351, MC-A760-5QX00]
- Department for International Development (DFID) under the MRC/DFID Concordat
- Department of Energy [DE-AC05-76RL0 1830]
- NIH [P41GM103493]
- MRC [MC_U105960371] Funding Source: UKRI
- Medical Research Council [MC_U105960371] Funding Source: researchfish
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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.
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