Treatment of paediatric hyperthyroidism but not hypothyroidism has a significant effect on weight.

objectiveThyroid hormones are involved in metabolic regulation, but the degree to which they affect body weight and body mass index (BMI) in children is unclear. We examined the effect of hypo- and hyperthyroidism on weight and BMI at the time of diagnosis and after appropriate treatment.

designProspective and retrospective case series. PATIENTS: Children referred for thyroid dysfunction were enrolled prospectively if their total or free T4 was elevated with TSH <0·05 mIU/ml (N = 57) or if they had a subnormal total or free T4 and TSH >20 (N = 29).

resultsAlmost all patients had at least 2 classic signs or symptoms including goitre, but hyperthyroid patients had more symptoms. Mean BMI z scores at the time of diagnosis did not significantly differ between the two groups. Males with hyperthyroidism complained of weight loss more frequently and had a lower pretreatment BMI z score than hyperthyroid females. Hypothyroid patients lost a minimal amount of weight by the first follow-up (mean of 0·3 kg) and on average gained weight by the second follow-up visit. In contrast hyperthyroid patients gained a mean of 3·4 kg at the first follow-up visit and a mean of 7·1 kg by the second.

conclusionsCorrection of hypothyroidism resulted in minimal weight loss, suggesting that hypothyroidism does not cause significant weight gain in children. In contrast, correction of the hyperthyroid state had a somewhat greater impact on weight status. These results are consistent with prior reports but surprising given the opposite metabolic effects of hypo- and hyperthyroidism.