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

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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.


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.


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).


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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