Relationship between the effect of eldecalcitol and serum 25(OH)D level

In previous studies, we demonstrated that 12-month treatment with 0.75 mu g/day eldecalcitol increased bone mineral density in osteoporotic patients regardless of serum 25-hydroxyvitamin D (25(OH)D) level, and in a 3-year randomized double-blind clinical trial, eldecalcitol significantly reduced the incidences of vertebral and wrist fractures compared to alfacalcidol. However, it remains unclear whether the fracture risk reduction by eldecalcitol is affected by serum 25(OH)D. In the fracture prevention trial, patients with low 25(OH)D level at baseline were supplemented with 400 IU/day native vitamin D3. In the current study, patients from that trial were divided according to the tertiles of serum 25(OH)D level at 6 months after treatment initiation. The increases in lumbar and hip BMD by eldecalcitol were significantly higher in all tertiles than those by alfacalcidol. The incidences of vertebral and osteoporotic fractures tended to be lower in each tertile of the eldecalcitol-treated group than in the corresponding tertile of the alfacalcidol-treated group, with the exception of vertebral fractures in the low tertile. We also investigated whether eldecalcitol treatment affected levels of serum 25(OH)D, serum 1,25(OH)2D, and parathyroid hormone in patients without vitamin D supplementation. With eldecalcitol treatment, serum 1,25(OH)2D concentration was reduced by approximately 50%, whereas serum levels of parathyroid hormone and 25(OH)D were not affected. The major findings of the present study were that eldecalcitol did not affect serum 25(OH)D levels, and that it reduced the incidence of osteoporotic fractures and increased BMD in comparison with alfacalcidol regardless of serum 25(OH)D level within the range of serum 25(OH)D concentrations at or higher than 20 ng/mL. Whether eldecalcitol is similarly effective at vitamin D deficient serum 25(OH)D levels remains to be clarified. This article is part of a Special Issue entitled 'Vitamin D Workshop'. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.