Childhood obesity, thyroid function, and insulin resistance – is there a link? A longitudinal study.

BACKGROUND: Serum thyroid stimulating hormone (TSH) levels are frequently elevated in obese children and are most likely to be associated with insulin resistance. However, clinical relevance of this association remains unclear.
OBJECTIVES: To assess the prevalence of hyperthyrotropinemia; to analyze the relationship between TSH and homeostasis model assessment - insulin resistance (HOMA-IR); and to verify whether TSH levels and HOMA-IR vary with weight loss in obese children. SUBJECTS AND METHODS: Retrospective longitudinal study with data from baseline and 1 year after lifestyle intervention in a pediatric obese group (344 children were recruited and 100 among them completed follow-up). For postintervention analysis, three groups were considered according to body mass index-standard deviation score (BMI-SDS) variations: ≤-0.5 (significant weight loss); 0.5-0 (weight loss); and >0 (weight gain). Statistical analysis was performed using SPSS 19.0®.
RESULTS: The prevalence of increased TSH levels was 9.3%. At baseline TSH (p=0.007), fT4 (p=0.006), and HOMA-IR (p<0.001) were positively correlated to BMI-SDS (n=344). Weight reduction was verified in 67 out of 100 cases but significant loss was present in only 21 cases. Decreases in both TSH and BMI-SDS were independently associated with decreases in HOMA-IR (p=0.005 and p=0.016, respectively). There was no correlation between TSH and BMI-SDS variation. Significant decreases in the HOMA-IR (p=0.006) were only achieved in the significant weight loss group.
CONCLUSIONS: The prevalence of hyperthyrotropinemia was lower than previously reported. However, cutoff values were adjusted to pubertal stage, suggesting an over report in other studies. Insulin resistance and TSH were positively correlated, independent of body status. Although weight loss was not associated with TSH variation, a decrease in TSH levels was independently associated with decreases in HOMA-IR.