The relationship between Hashimoto's thyroiditis and vitamin D has been demonstrated in several studies. The aim of the present study was to evaluate vitamin D concentrations in patients with Hashimoto's thyroiditis, the effect of vitamin D therapy on the course of disease, and to determine changes in thyroid autoantibody status and cardiovascular risk after vitamin D therapy. We included 75 patients with Hashimoto's thyroiditis and 43 healthy individuals. Vitamin D deficiency is defined as a 25-hydroxy vitamin D (25(OH)D3) concentration less than 20ng/mL. Vitamin D deficient patients were given 50.000 units of 25(OH)D3 weekly for eight weeks in accordance with the Endocrine Society guidelines. All evaluations were repeated after 2 months of treatment. Patients with Hashimoto's thyroiditis had significantly lower vitamin D concentrations compared with the controls (9.37±0.69 ng/mL vs 11.95±1.01 ng/mL, p < 0.05, respectively). Thyroid autoantibodies were significantly decreased by vitamin D replacement treatment in patients with euthyroid Hashimoto's thyroiditis. Also, HDL cholesterol concentrations improved in the euthyroid Hashimoto group after treatment. The mean free thyroxine (fT4) concentrations were 0.89±0.02 ng/dL in patients with Hashimoto's thyroiditis and 1.07±0.03 ng/dL in the healthy control group (p < 0.001). The mean thyroid volumes were 7.71±0.44 mL in patients with Hashimoto's thyroiditis and 5.46±0.63 mL in the healthy control group (p < 0.01). Vitamin D deficiency is frequent in Hashimoto's thyroiditis and treatment of patients with this condition with Vitamin D may slow down the course of development of hypothyroidism and also decrease cardiovascular risks in these patients. Vitamin D measurement and replacement may be critical in these patients.
Keywords: cardiovascular risk; hashimoto's thyroiditis; vitamin D.