**9. Thyroid diseases and CD**

It is well known that CD is present in a higher proportion of patients with autoimmune-based thyroid diseases (e.g., Graves' disease and Hashimoto's thyroiditis), with a prevalence of 2–7% [62–65]. Similar observations have been made in celiac patients, whereby their serological signs of autoimmune thyroid disease were present in up to 26% of cases. Thyroid dysfunction was detected in up to 10% of the cases of CD and it was estimated that the risk of disease was at least three times higher than in healthy controls [66–69].

It has been reported that patients with CD who follow a GFD could develop thyroid problems of an autoimmune nature. In contrast, other studies have described declining anti-thyroid antibody titres after a period of 2–3 years on the GFD [70, 71]. These different results could have arisen because patients had been on their GFD for different lengths of time. The authors prospectively evaluated the presence of thyroid autoimmunity in children and adolescents with CD who had adopted a GFD. After 2 years on the diet, a 7% increase in thyroid autoimmunity was observed, based on levels of l-thyroxine in the CD patients. Thyroid autoimmunity did not appear to be more frequent in paediatric patients and adolescents with CD who followed a GFD than in control groups. Since their clinical development does not seem to affect growth, the authors concluded that a long-term programme screening for thyroid disease might not be necessary for all patients with CD who follow a GFD, but may be advisable for those for whom there is a suspicion of thyroid disease [72].

The coexistence of CD and autoimmune thyroid disease has been explained in terms of several mechanisms, such as the genetic predisposition and the association of both diseases with the gene that codes for antigen 4, which is associated with cytotoxic T lymphocytes and which confers susceptibility to thyroid autoimmunity. It has also been shown that the tTG-2 IgA reacts with thyroid tissue and that this association could contribute to the onset and development of thyroid disease in patients with CD [73].
