Serum Vitamin D Deficiency Is an Independent Risk Factor for Thyroid Eye Disease

Purpose: Thyroid eye disease (TED) is an inflammatory orbitopathy with significant impact on visual function and quality of life. Although studies have shown that patients who are deficient in vitamin D are more likely to develop autoimmune conditions, there are no studies demonstrating a definitive correlation between serum 25-hydroxyvitamin D (25(OH)D) deficiency and an increased risk of TED. Methods: This retrospective case-control study compared serum 25(OH)D levels among 4 groups: 1) Graves disease (GD) patients with TED (n = 89); 2) GD patients without TED (n = 89); and healthy control patients matched to 3) the TED group (n = 356); and 4) the GD group (n = 356). The authors compared 25(OH)D level in the TED group measured within 1 year of TED diagnosis to the most recently measured 25(OH)D level in the GD group using Student t test of the log transformation of serum levels. Linear regression was used to control for other risk factors. Thyroid eye disease patients and GD patients were compared separately to their matched healthy control patients with linear mixed models. Results: Thyroid eye disease patients displayed significantly lower serum 25(OH)D levels than GD patients (24.8 ± 13.2 ng/ml vs. 29.4 ± 13.3 ng/ml; p = 0.006). Controlling for smoking status and previous radioactive iodine treatment did not affect this statistically significant difference. Conclusions: Low serum vitamin D is associated with TED diagnosis. Assessing and supplementing vitamin D levels may be an important addition to the early management of GD patients. Future research should include longitudinal studies and prospective clinical trials to further explore the mechanism responsible for the observed association.