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J Clin Endocrinol Metab. 2015 Sep;100(9):3356-63. doi: 10.1210/JC.2015-2066. Epub 2015 Jul 10.

Free 25(OH)D and the Vitamin D Paradox in African Americans.

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1
Winthrop University Hospital, Mineola, New York 11501.

Erratum in

Abstract

CONTEXT:

African Americans have a lower total serum 25-hydroxyvitamin D [25(OH)D] but superior bone health. This has been referred to as a paradox. A recent publication found that free serum 25(OH)D is the same in black and white individuals. However, the study was criticized because an indirect method was used to measure free 25(OH)D. A direct method has recently been developed.

OBJECTIVE:

We hypothesized that although total serum 25(OH)D is lower in African Americans, free serum 25(OH)D measured directly would not differ between races.

DESIGN:

White and black healthy postmenopausal women were matched for age and body mass index. Serum total 25(OH)D, PTH, 1,25-dihydroxyvitamin D, vitamin D binding protein (VDBP), and bone density were measured. Measurement of free 25(OH)D was carried out using an ELISA.

SETTING:

The study was conducted at an ambulatory research unit in a teaching hospital.

OUTCOME:

A cross-racial comparison of serum free 25(OH)D was performed.

RESULTS:

A propensity match resulted in the selection of a total of 164 women. Total 25(OH)D was lower in black women (19.5 ± 4.7 vs 26.9 ± 6.4 ng/mL), but a direct measurement of free 25(OH)D revealed almost identical values (5.25 ± 1.2 vs 5.25 ± 1.3 ng/mL) between races. VDBP was significantly lower in blacks when using a monoclonal-based ELISA but higher with a polyclonal-based ELISA. Serum PTH, 1,25-dihydroxyvitamin D, and bone density were higher in African Americans.

CONCLUSIONS:

Free serum 25(OH)D is the same across races despite the lower total serum 25(OH)D in black women. Results comparing VDBP between races using a monoclonal vs a polyclonal assay were discordant.

PMID:
26161453
PMCID:
PMC4570168
DOI:
10.1210/JC.2015-2066
[Indexed for MEDLINE]
Free PMC Article

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