Objective: The impact of thyroid hormones on weight loss in lifestyle interventions and on weight regain afterwards is unknown. Therefore, we studied the relationships between TSH, free triiodothyronine (fT₃), free thyroxine (fT₄), and weight status, as well as their changes during and after a lifestyle intervention in obese children.
Materials and methods: We evaluated the weight status as BMI-SDS in 477 obese children (mean age 10.6±2.7 years, 46% male, mean BMI 28.1±4.5 kg/m²) participating in a 1-year lifestyle intervention in a 2-year longitudinal study. Changes in BMI-SDS at 1 and 2 years were correlated with TSH, fT₃, and fT₄ concentrations at baseline and their changes during the intervention.
Results: A decrease in BMI-SDS during the intervention period (-0.32±0.38; P<0.001) was significantly positively associated with baseline TSH and fT₃ in multiple linear regression analyses adjusted for age, sex, pubertal stage, and baseline BMI-SDS. An increase in BMI-SDS after the end of the intervention (+0.05±0.36; P=0.011) was significantly related to the decreases in TSH and fT₃ during the intervention in multiple linear regression analyses adjusted for change in BMI-SDS during the intervention. In contrast to children with weight maintenance, children with weight regain after the end of the intervention demonstrated a decrease in their TSH levels (-0.1±1.6 vs +0.2±1.6 mU/l; P=0.03) and fT₃ (-0.2±1.1 vs +0.3±1.6 pg/ml; P<0.001) during the intervention.
Conclusions: The decreases in TSH and fT₃ concentrations during the lifestyle intervention were associated with weight regain after the intervention. Future studies should confirm that the decreases in TSH and fT₃ levels associated with weight loss are related to the change in metabolism such as resting energy expenditure.
Trial registration: ClinicalTrials.gov NCT00435734.