Relative Vitamin D Insufficiency in Hashimoto's Thyroiditis

Background: Vitamin D insufficiency, defined as serum levels of 25-hydroxyvitamin D [25(OH)D3] lower than 30 ng/mL, has been reported to be prevalent in several autoimmune diseases such as multiple sclerosis and type 1 diabetes mellitus. The goal of the present study was to assess whether vitamin D insufficiency is also a feature of Hashimoto's thyroiditis (HT). Methods: We performed a prevalence case-control study that included 161 cases with HT and 162 healthy controls. Serum levels of 25(OH) D3, calcium, phosphorus, and parathyroid hormone were measured in all 323 subjects. Results: The prevalence of vitamin D insufficiency in HT cases (148 of 161, 92%) was significantly higher than that observed in healthy controls (102 of 162, 63%, p < 0.0001). Among HT cases, the prevalence rate of vitamin D insufficiency showed a trend to be higher in patients with overt hypothyroidism (47 of 50, 94%) or subclinical hypothyroidism (44 of 45, 98%) than in those with euthyroidism (57 of 66, 86%), but the differences were not significant (p = 0.083). Conclusion: Vitamin D insufficiency is associated with HT. Further studies are needed to determine whether vitamin D insufficiency is a casual factor in the pathogenesis of HT or rather a consequence of the disease.