Calculated free and bioavailable vitamin D metabolite concentrations in vitamin
D-deficient hip fracture patients after supplementation with cholecalciferol and
ergocalciferol.
Author(s): Glendenning P(1), Chew GT, Inderjeeth CA, Taranto M, Fraser WD.
Affiliation(s): Author information:
(1)Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital,
Perth, Western Australia, Australia. Paul.Glendenning@health.wa.gov.au
Publication date & source: 2013, Bone. , 56(2):271-5
We previously showed that oral cholecalciferol and ergocalciferol have comparable
effects in decreasing circulating parathyroid hormone (PTH), despite a greater
increase in total serum 25-hydroxyvitamin D (25OHD) concentration with
cholecalciferol supplementation. However, the effects of cholecalciferol and
ergocalciferol on total serum 1,25-dihydroxyvitamin D (1,25(OH)2D), vitamin
D-binding protein (DBP), free 25OHD and free 1,25(OH)2D concentrations have not
been previously studied. We randomized 95 hip fracture patients (aged 83±8 years)
with vitamin D deficiency (serum 25OHD <50 nmol/L) to oral supplementation with
either cholecalciferol 1000 IU/day (n=47) or ergocalciferol 1000 IU/day (n=48)
for three months. All were given matching placebos of the alternative treatment
to maintain blinding. We measured serum 25OHD (high-pressure liquid
chromatography), 1,25(OH)2D (Diasorin radioimmunoassay), DBP
(immunonephelometry), ionized calcium (Bayer 800 ion-selective electrode) and
albumin (bromocresol green) concentrations before and after treatment. We
calculated free and bioavailable concentrations of the vitamin D metabolites
using albumin and DBP, and calculated free vitamin D metabolite indices as the
ratios between the molar concentrations of the vitamin D metabolites and DBP.
Seventy participants (74%) completed the study with paired samples for analysis.
Total serum 1,25(OH)2D did not change significantly with either treatment
(p>0.05, post-treatment vs baseline). Both treatments were associated with
comparable increases in DBP (cholecalciferol: +18%, ergocalciferol: +16%, p=0.32
between groups), albumin (cholecalciferol: +31%, ergocalciferol: +21%, p=0.29
between groups) and calculated free 25OHD (cholecalciferol: +46%, ergocalciferol:
+36%, p=0.08), with comparable decreases in free 1,25(OH)2D (cholecalciferol:
-17%, ergocalciferol: -19%, p=0.32 between groups). In the treatment-adherent
subgroup the increase in ionized calcium was marginally greater with
cholecalciferol compared with ergocalciferol (cholecalciferol: +8%,
ergocalciferol: +5%, p=0.03 between groups). There were no significant
differences between the treatments in their effects on the calculated
bioavailable concentrations or free indices of the vitamin D metabolites (p>0.05
between groups). In vitamin D-deficient hip fracture patients, oral
supplementation with cholecalciferol and ergocalciferol had no effect on total
serum 1,25(OH)2D, and comparable effects on DBP and free vitamin D metabolite
concentrations. This is despite cholecalciferol having greater effects than
ergocalciferol in increasing total 25OHD, and in increasing ionized calcium in
treatment-adherent subjects. These findings may explain why cholecalciferol and
ergocalciferol supplementation result in similar magnitudes of PTH reduction, but
implicate potential differences in other vitamin D metabolites, such as
24,25(OH)2D, that could explain their different effects on ionized calcium.
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