Gluten-free diet attenuates the impact of exogenous vitamin D on thyroid autoimmunity in young women with autoimmune thyroiditis: a pilot study.

Although both exogenous vitamin D and a gluten-free diet were found to reduce thyroid antibody titers, no study investigated interactions between gluten intake and vitamin D status in patients with autoimmune thyroid disorders. The aim of the present study was to assess whether the gluten-free diet determines the effect of vitamin D treatment on thyroid autoimmunity and thyroid function in young women with autoimmune (Hashimoto's) thyroiditis. The study compared two groups of euthyroid premenopausal women with this disorder, matched for thyroid antibody titers: 31 women with non-celiac gluten sensitivity complying for at least 12 months with the gluten-free diet and 31 unaffected sisters of women with non-celiac gluten sensitivity remaining without any dietary intervention. Plasma titers of thyroid peroxidase and thyroglobulin antibodies, as well as plasma concentrations of thyrotropin, free thyroid hormones, prolactin, 25-hydroxyvitamin D and high-sensitive C-reactive protein were measured at entry and after a six-month follow-up. Moreover, at both time points, the structure parameters of thyroid homeostasis were assessed. Although exogenous vitamin D decreased titers of thyroid peroxidase and thyroglobulin antibodies and increased 25-hydroxyvitamin D levels in each treatment group, this effect was less pronounced in patients on the gluten-free diet than in patients not following any dietary recommendations. Only in the latter group of patients, vitamin D increased SPINA-GT. Treatment-induced changes in thyroid peroxidase and thyroglobulin antibodies correlated with the impact of treatment on 25-hydroxyvitamin D levels. The obtained results suggest that gluten-free diet may impair beneficial effects of exogenous vitamin D in individuals with Hashimoto's thyroiditis.