Vitamin D binding protein is not affected by high-dose vitamin D supplementation: a post hoc analysis of a randomised, placebo-controlled study

Linda Björkhem-Bergman, Emelie Torefalk, Lena Ekström, Peter Bergman, Linda Björkhem-Bergman, Emelie Torefalk, Lena Ekström, Peter Bergman

Abstract

Objectives: Vitamin D binding protein (VDBP) is the main transporter of 25-hydroxyvitamin D3 (25-OHD) in the circulation. The aim of this study was to investigate if VDBP is affected by high dose vitamin D supplementation and if VDBP-levels correlate with free 25-OHD. Correlation between free 25-OHD measured with ELISA and total 25-OHD in the circulation was also analysed. Plasma samples from a randomized, controlled trial in which persistent MRSA-carriers were randomized to treatment with vitamin D, 4000 IE/day, (n = 27) or placebo (n = 32) for 12 months were used. Plasma from baseline and after 6 months of treatment were analysed for VDBP, 25-OHD and free 25-OHD.

Results: VDBP levels were not affected by vitamin D treatment, although the 25-OHD levels increased significantly in the vitamin D treated subjects. There was a strong correlation between 25-OHD and free 25-OHD (r2 = 0.68, p < 0.0001), while there was no correlation between VDBP and free 25-OHD. Thus, our data shows that VDBP are not affected by vitamin D supplementation and the levels of VDBP are not associated with the free fraction of 25-OHD. Since there was a strong correlation between free 25-OHD and total 25-OHD it appears to be sufficient to measure only total 25-OHD. Trial registration http://www.clinicaltrials.gov ; NCT02178488. Date of registration: June 30, 2014; Date of enrolment of the first participant: Dec 1, 2014.

Keywords: Free 25-hydroxyvitamin D; MRSA; Vitamin D; Vitamin D binding protein.

Figures

Fig. 1
Fig. 1
Plasma levels of a vitamin D binding protein (VDBP), b 25-hydroxyvitamin D (25-OHD) and c free fraction of 25-OHD in the placebo group and the vitamin D treated group at baseline and after 6 months in the original study [10]
Fig. 2
Fig. 2
Correlation between a free 25-hydroxyvitamin D (25-OHD) and b 25-OHD and between free 25-OHD and vitamin D binding protein (VDBP) in plasma samples from the original study at baseline and after 6 months (n = 118)

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