Ponda Manish P, McGee David, Breslow Jan L
Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, New York, New York 10065.
J Clin Endocrinol Metab. 2014 Jul;99(7):2494-9. doi: 10.1210/jc.2014-1181. Epub 2014 Apr 8.
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.
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.
维生素D缺乏症由血清总25-羟基维生素D[25(OH)D]水平定义，较为常见，在黑人中比白人更为普遍。维生素D结合蛋白(DBP)水平因种族而异，可能会调节25(OH)D的“生物可利用”水平。
确定DBP水平对维生素D功能反应的影响。
一项在门诊研究单位进行的为期2个月的维生素D补充随机、安慰剂对照试验。参与者包括150名维生素D缺乏(25(OH)D<20 ng/mL)的成年人。参与者被随机分配，每周接受50000 IU维生素D3或安慰剂，共8周。这是一项使用DBP、25(OH)D、甲状旁腺激素(PTH)和钙水平的事后分析。
黑人的总25(OH)D(12 vs 15 ng/mL，P<.001)和DBP水平(119 vs 234 μg/mL，P<.001)低于非黑人。维生素D3或安慰剂治疗前后DBP水平相似(r = 0.98，P<.001)。基线总25(OH)D水平是基线PTH水平的重要决定因素(P<.001)。总25(OH)D的变化与PTH的变化(P<.001)和钙水平的变化(P<.05)相关。相比之下，DBP水平不是基线PTH的决定因素(P = .57)，与PTH(P = .53)或钙水平(P = .88)的变化也无显著相关性。
黑人与非黑人的DBP水平稳定，不会因维生素D缺乏的纠正而改变。即使对于总25(OH)D水平<20 ng/mL的个体，黑人的DBP水平也显著低于非黑人。然而，在这个总25(OH)D范围内，DBP水平不影响维生素D补充对PTH或钙水平的作用。
