Objective: Alterations in thyroid function are reported in obesity although no relevant data exist, on the thyroid structure of these patients and the frequency of autoimmunity. The aim of our study was to evaluate the involvement of the thyroid gland in a large group of obese children.

Design: A cross-sectional study

Methods: The study was conducted between March 2004 and December 2007 in 186 overweight and obese children. In all subjects, serum fT3, fT4, TSH, anti-thyroid-antibodies and a thyroid ultrasound were assessed. Forty healthy children matched for age and of normal weight for height served as controls.

Results: Twenty-three children (12.4%) showed anti-thyroid antibodies and an ultrasound pattern suggestive of Hashimoto's thyroiditis (group A). Twenty of them (10.8%) showed anti-thyroid antibodies and normal ultrasound (group B). Seventy subjects (37.6%) showed absent anti-thyroid antibodies and an ultrasound pattern suggestive of Hashimoto thyroiditis (group C), and 73 children (39.2%) showed no thyroid-antibodies with normal ultrasound (group D). TSH was higher in groups A and C compared to group B, group C and controls (P<0.05). Mean fT4 was lower in group B (P<0.05) than in controls, while fT3 was higher in group C than in controls (P<0.05). TSH and BMI SDS were significantly correlated in group C (P<0.001) and TSH was also significantly associated with the degree of thyroid structure alterations (Ps<0.05).

Conclusions: Obese children frequently show alterations of thyroid structure and function that are not completely explained by the presence of an autoimmune involvement.