Endocrine Abstracts

Background: Vitamin D is important to skeletal health and is standard care in conditions with low BMD. Thyrotoxicosis caused by Graves’ disease (GD) leads to increased bone turnover and reduced BMD. We aimed to test the hypothesis that vitamin D supplementation would improve bone recovery in GD.

Methods: Using a double-blinded design, hyperthyroid patients with a first time diagnosis of GD were randomized to supplementation with vitamin D3 70 mg/day or placebo as add-on to standard therapy with anti-thyroid drugs (ATD). At baseline and nine months, we measured bone mass density, body composition and bone architecture using DXA and HRpqCT. Between-group differences in change and response to ATD treatment were analyzed using linear mixed modelling. In subanalysis, we tested for interaction between the intervention and baseline vitamin status (insufficient (<50 nmol/l or replete). (The DAGMAR study clinicaltrials.gov #NCT02384668).

Results: 86 GD patients were included (86% females, mean age 41 ± 14). Compared with placebo, nine months of vitamin D3 did not significantly improve bone density or architecture. However, vitamin D3 tended to reduce gain in lean body mass (−24%, P = 0.08), fat mass (−49%, P = 0.21) and body weight (−33%, P = 0.09). Vitamin D3 did not affect changes in plasma levels of thyroid hormones or TRAb. In response to ATD, BMD increased significantly in hip 2% (95% CI : 1–4). Cortical porosity decreased, tibia −7% (95% CI : −12 to −2) and radius −14% (95% CI : −24 to −3), and trabecular thickness increased, tibia 5% (95% CI : 2–9) and radius 4% (95% CI : 1–7). Stiffness and estimated failure load did not change significantly. Lean body mass increased 10% (95% CI : 8–12). In subanalysis of all outcomes, the effect of intervention did not differ between patients with a baseline insufficient as opposed to replete vitamin D status.

Conclusion: In newly diagnosed GD, nine months of high dose vitamin D3 supplementation does not offer benefit in improving skeletal health but may adversely affect restoration of body composition. Treatment of thyrotoxicosis is of major importance to restore bone density and microarchitecture.