Elevated serum levels of free triiodothyronine in adolescent boys with gynaecomastia compared with controls.

OBJECTIVE Pubertal gynaecomastia is a frequent phenomenon occurring in 20-40% of otherwise healthy adolescent boys. Little is known about the aetiology of pubertal gynaecomastia. Markedly elevated thyroid hormone levels in adults with hyperthyroidism are associated with gynaecomastia. DESIGN A cross-sectional examination of 444 healthy boys with and without pubertal gynaecomastia. METHODS We evaluated TSH, triiodothyronine (T3), thyroxine (T4), free T4 and free T3 in a cohort of healthy boys with and without pubertal gynaecomastia. RESULTS Boys with gynaecomastia had significantly higher serum free T3, even after correction for age, BMI and pubertal stage. After inclusion of IGF1 in the model the differences disappeared. TSH, T4, free T4 and T3 did not differ between the groups. CONCLUSIONS We speculate that the GH/IGF1 axis and thyroid hormones interact and influence the development of pubertal gynaecomastia.