Relationship between Thyroid Volume and Baseline Vitamin D Levels in New-Onset Graves Disease

Abstract

Objective: Serum vitamin D is shown to be decreased and associated with higher thyroid volumes in Graves disease (GD). We aimed to investigate the relationship between thyroid volume and baseline serum vitamin D status in newly diagnosed GD patients.

Methods: This was a single-center cross-sectional study with a total of 61 new-onset GD patients (n=61, F: 40, M: 21) who were divided into two groups, according to baseline serum vitamin D levels, as Group-1 (vitamin D <20; n: 42) and Group-2 (vitamin D =20; n=19). Thyroid volume (mL) and isthmus measurements (mm) were compared between the two groups.

Results: There was an inverse correlation between the baseline serum vitamin D levels and thyroid volume, thyroid receptor autoantibodies (TRAb), free triiodothyronine (fT3), and parathyroid hormone (PTH) levels (p=0.02, r=-0.31; p=0.005, r=-0.36; p=0.04, r=-0.26; p=0.02, r=-0.32, respectively). Thyroid volume was also correlated with serum free thyroxine (fT4), fT3, TRAb, and thyroid peroxidase autoantibodies (TPOAb; p=0.001, r=0.426; p=0.001, r=0.50; p=0.04, r=0.26; p=0.001, r=0.42, respectively). Low vitamin D and high thyroglobulin antibody (TgAb) levels were significantly associated with thyroid volume based on a regression analysis (p=0.03, odds ratio [OR]: 18.7, 95% confidence interval [CI]: 1.34-260.91 and p=0.04, OR: 16.6, 95% CI: 1.07-255.64, respectively).

Conclusion: Baseline serum vitamin D levels are inversely related with thyroid volumes, fT3, and TRAb levels in new-onset GD. In addition to several advantages, optimization of vitamin D levels would also be beneficial in the surveillance of these patients. However, larger scale studies are required to make further suggestions.