Endocrine Abstracts

Background: Vitamin D deficiency has been proposed to play a role in development and course of Graves’ disease (GD). Muscle weakness and fatigue are shared features of GD and vitamin D deficiency. We aimed to investigate whether vitamin D supplementation would improve restoration of muscle performance and thyroid-related quality of life (QoL) in GD.

Methods: In a double-blinded clinical trial, hyperthyroid patients with a first time diagnosis of GD were randomized to vitamin D 70 mcg/day or matching placebo as add-on to standard antithyroid medication (ATD). At baseline and after three and nine months of intervention, we assessed isometric muscle strength, muscle function tests, postural stability, body composition, and self-reported ThyPRO Tiredness and Impaired Daily Life (0–100, higher score worse). Differences in change between groups were analyzed using linear mixed modelling. (The DAGMAR study clinicaltrials.gov ID NCT02384668).

Results: Nine months of vitamin D supplementation caused a reduced muscle strength increase at all muscle groups investigated, although only significant at knee extension 60° with a 7% (95% CI:0.3;13) lower increase in muscle strength compared with placebo. Vitamin D supplementation showed a trend towards reduced gain of lean body mass (−3.1% (95% CI:−6.5;0.4)). There was no significant difference in Tiredness or Impaired Daily Life, but improvement of Impaired Daily Life tended to be lower in the vitamin D group (10 points (95% CI:−2;22)). In the entire group of patients, all measures improved significantly in response to nine months of ATD with an improvement of 21–37% in muscle strength at the different muscle groups (P_all<0.001) and of 11% (95% CI:9;13) in lean body mass. Furthermore, performance of the repeated chair stand test and the time-up-and-go test improved by 15% (95% CI:12;18) and 2% (95% CI:0.4;5). Postural stability improved by 26–54% P_all<0.001. Large changes was observed in Tiredness and Impaired Daily Life with improvements of 22 (95% CI:19;26) and 36 (95% CI:28;45) points. In general, improvements were most marked during the first three months of ATD, but the recovery continued from three to nine months.

Conclusion: Nine months of vitamin D supplementation 70 mcg/day caused unfavorable effects on restoration of muscle performance. In contrast, ATD treatment was associated with marked improvement in all measures of muscle performance and thyroid-related QoL. In patients with newly diagnosed GD, high dose vitamin D supplementation should not be recommended to improve muscle function, but ATD therapy seems to be of major importance to alleviate muscle impairment.