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

• Published in: The journal of clinical endocrinology and metabolism Vol. 99; no. 7; pp. 2494 - 2499
• Main Authors: Ponda, Manish P, McGee, David, Breslow, Jan L
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01.07.2014; Copyright by The Endocrine Society
• Subjects: Adult; Calcium - blood; Cholecalciferol - blood; Cholecalciferol - pharmacology; Dietary Supplements; Endocrine Research; Female; Humans; Male; Middle Aged; Parathyroid Hormone - blood; Vitamin D - analogs & derivatives; Vitamin D - blood; Vitamin D Deficiency - blood; Vitamin D Deficiency - drug therapy; Vitamin D-Binding Protein - blood
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jc.2014-1181

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.