Free 25(OH)D and the Vitamin D Paradox in African Americans - PubMed (original) (raw)

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

John Aloia et al. J Clin Endocrinol Metab. 2015 Sep.

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.

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Figures

Figure 1.

Figure 1.

Distribution of total 25(OH)D by race. Mean total 25(OH)D is lower in black than white women. The mean level for this population is near the estimated average requirement (EAR) for the black population and above it for the white population.

Figure 2.

Figure 2.

Relationships between total 25(OH)D and free 25(OH)D by race.

Figure 3.

Figure 3.

Distribution of VDBP (micrograms per milliliter; both monoclonal and polyclonal antibody) by race. The monoclonal assay is similar to the total 25(OH)D in that the white women clearly had higher values than the African Americans.

References

    1. Institute of Medicine (US) Committee to Review Dietary. Reference intakes for vitamin D and calcium. Ross AC, Taylor CL, Yaktine AL, Del Valle HB, eds. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academies Press; 2011. http://www.ncbi.nlm.nih.gov/books/NBK56070. -PubMed
    1. Armas LA, Dowell S, Akhter M, et al. Ultraviolet-B radiation increases serum 25-hydroxyvitamin D levels: the effect of UVB dose and skin color. J Am Acad Dermatol. 2007;57(4):588–593. -PubMed
    1. Aloia JF, Vaswani A, Feuerman M, Mikhail M, Ma R. Differences in skeletal and muscle mass with aging in black and white women. Am J Physiol Endocrinol Metab. 2000;278(6):E1153–E1157. -PubMed
    1. Kleerekoper M, Nelson DA, Peterson EL, et al. Reference data for bone mass, calciotropic hormones, and biochemical markers of bone remodeling in older (55–75) postmenopausal white and black women. J Bone Miner Res. 1994;9(8):1267–1276. -PubMed
    1. Aloia JF, Vaswani A, Yeh JK, Flaster E. Risk for osteoporosis in black women. Calcif Tissue Int. 1996;59(6):415–423. -PubMed

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