Vitamin D Binding Protein Impact on 25-Hydroxyvitamin D Levels under Different Physiologic and Pathologic Conditions.

Pegah Yousefzadeh,Xiangbing Wang,Sue A Shapses

doi:10.1155/2014/981581

Abstract

There is a high prevalence of vitamin D deficiency worldwide, but how to define vitamin D deficiency is controversial. Currently, the plasma concentration of total 25-hydroxyvitamin D [25(OH)D] is considered an indicator of vitamin D status. The free hormone hypothesis states that protein-bound hormones are inactive while unbound hormones are free to exert biological activity. The majority of circulating 25(OH)D and 1,25(OH)2D is tightly bound to vitamin D binding protein (DBP), 10–15% is bound to albumin, and less than 1% of circulating vitamin D exists in an unbound form. While DBP is relatively stable in most healthy populations, a recent study showed that there are gene polymorphisms associated with race and ethnicity that could alter DBP levels and binding affinity. Furthermore, in some clinical situations, total vitamin D levels are altered and knowing whether DBP is also altered may have treatment implications. The aim of this review is to assess DBP concentration in different physiological and pathophysiological conditions. We suggest that DBP should be considered in the interpretation of 25(OH)D levels.

Highlights

Reports of the worldwide prevalence of low vitamin D status vary depending on the level of total 25-hydroxyvitamin D [25(OH)D] that is used to define vitamin D sufficiency
Recent studies have found that serum D binding protein (DBP) and vitamin D levels are decreased in type 1 diabetes mellitus (T1DM) [9], chronic liver [10], and renal diseases [11], while pregnancy and oral contraceptive pills (OCP) increase DBP and vitamin D levels [12, 13]
Another study showed that urinary loss of DBP in T1DM was higher compared to healthy individuals suggesting that urinary loss of DBP might contribute to the lower levels of serum 25(OH)D [40]

Summary

Introduction

Reports of the worldwide prevalence of low vitamin D status vary depending on the level of total 25-hydroxyvitamin D [25(OH)D] that is used to define vitamin D sufficiency. It was reported that despite the lower levels of total 25(OH)D and DBP in blacks compared to whites, both groups had similar concentrations of estimated bioavailable 25(OH)D and can be explained by a difference in polymorphisms in the DBP gene [5]. Recent studies have found that serum DBP and vitamin D levels are decreased in type 1 diabetes mellitus (T1DM) [9], chronic liver [10], and renal diseases [11], while pregnancy and oral contraceptive pills (OCP) increase DBP and vitamin D levels [12, 13].

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