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Randomized Controlled Trial
. 2014 Jul;99(7):2494-9.
doi: 10.1210/jc.2014-1181. Epub 2014 Apr 8.

Vitamin D-binding protein levels do not influence the effect of vitamin D repletion on serum PTH and calcium: data from a randomized, controlled trial

Manish P Ponda  1 , David McGee, Jan L Breslow
Affiliations
Randomized Controlled Trial

Vitamin D-binding protein levels do not influence the effect of vitamin D repletion on serum PTH and calcium: data from a randomized, controlled trial

Manish P Ponda et al. J Clin Endocrinol Metab. 2014 Jul.

Abstract

Context: Vitamin D deficiency, defined by the total serum 25-hydroxyvitamin D [25(OH)D] level, is common and more prevalent among Blacks than whites. Vitamin D-binding protein (DBP) levels vary with race and may modulate "bioavailable" levels of 25(OH)D.

Objective: To determine the effect of DBP levels on the functional response to vitamin D.

Setting and design: A randomized, placebo-controlled trial of vitamin D repletion for 2 mo, which took place at an outpatient research unit. Participants included 150 vitamin D-deficient (25(OH)D <20 ng/mL) adults. Participants were randomly assigned to receive either 50,000 IU of vitamin D3 or placebo weekly for 8 weeks. This is a post-hoc analysis using DBP, 25(OH)D, PTH, and calcium levels.

Results: Blacks had lower total 25(OH)D (12 vs 15 ng/mL, P < .001) and DBP levels (119 vs 234 μg/mL, P < .001) than non-Blacks. DBP levels were similar before and after vitamin D3 or placebo treatment (r = 0.98, P < .001). Baseline total 25(OH)D levels were a significant determinant of baseline PTH levels (P < .001). The change in total 25(OH)D was associated with the change in PTH (P < 0.001) and calcium levels (P < .05). In contrast, DBP levels were not a determinant of baseline PTH (P = .57) nor significantly related to changes in either PTH (P = .53) or calcium levels (P = .88).

Conclusions: DBP levels are stable in Blacks and non-Blacks, and do not change with correction of vitamin D deficiency. Even for individuals with total 25(OH)D levels < 20 ng/mL, Blacks have significantly lower DBP levels than non-Blacks. However, within this range of total 25(OH)D, DBP levels do not influence the effect of vitamin D repletion on PTH or calcium levels.

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Figures

Figure 1.
Figure 1.
The correlation between baseline and final DBP levels (μg/mL) in Blacks (closed circles) and non-Blacks (open circles) receiving vitamin D3 (left) or placebo (right).
See this image and copyright information in PMC

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