Moderate-dose simvastatin therapy potentiates the effect of vitamin D on thyroid autoimmunity in levothyroxine-treated women with Hashimoto's thyroiditis and vitamin D insufficiency.

BACKGROUND: Vitamin D preparations reduce titers of thyroid antibodies in women with autoimmune thyroiditis. The same effect was induced by high-dose, but not moderate-dose-, statin therapy. No previous study has investigated the impact of concomitant treatment with a statin and vitamin D on thyroid autoimmunity.

METHODS: The study included three matched groups of women with Hashimoto's thyroiditis and low vitamin D status. Groups B (n=19) and C (n=20) were treated with vitamin D (2000 IU daily). Because of coexistent hypercholesterolemia, groups A (n=18) and B received simvastatin (40mg daily). Plasma lipids, serum levels of thyrotropin, free thyroid hormones and 25-hydroxyvitamin D, as well as titers of thyroid peroxidase and thyroglobulin antibodies were measured at the beginning of the study and 6 months later.

RESULTS: At baseline, 25-hydroxyvitamin D levels inversely correlated with titers of thyroid antibodies. In groups A and B, simvastatin reduced plasma levels of total and LDL cholesterol. Simvastatin produced no effect on thyroid antibody titers. Vitamin D decreased titers of thyroid peroxidase antibodies, as well as tended to decrease titers of thyroglobulin antibodies. Simvastatin-vitamin D combination therapy reduced serum titers of thyroid peroxidase and thyroglobulin antibodies and this effect was stronger than the effect of simvastatin and vitamin D administered alone. Treatment-induced changes in thyroid antibody titers correlated with baseline antibody titers, baseline levels of 25-hydroxyvitamin and treatment-induced changes in 25-hydroxyvitamin.

CONCLUSIONS: The obtained results indicate that simvastatin may potentiate the impact of vitamin D on thyroid autoimmunity in vitamin D-deficient women with Hashimoto's thyroiditis.