Children with congenital hypothyroidism are at risk of adult obesity due to early adiposity rebound

OBJECTIVE There is some evidence that children with congenital hypothyroidism (CH) are heavier than their reference population. There are few data on adults with CH. The timing of adiposity rebound (AR) in childhood has been shown to have strong correlations with adult obesity. Our aims were to study the timing of AR and factors affecting AR in children with CH. PATIENTS AND METHODS The timing of AR was examined in a retrospective study of children with CH with growth data at least up to 5 years of age. The proportion of children with CH who reached AR by 37 months and by 49 months of age were compared with healthy children and children with acute lymphoblastic leukaemia (ALL) described in the literature. Correlation of timing of AR with body mass index (BMI) standard deviation score (SDS) at 10 years, initial severity of hypothyroidism and age at normalization of TSH were examined. Multiple logistic regression was used to identify independent factors associated with BMI greater than or equal to 20 (overweight) at 10 years of age. RESULTS The study included 53 children (34 females and 19 males). AR had occurred by 37 months in 37.7% children with CH, in 42.7% children treated for ALL (CH vs. ALL, P = 0.58) and in 4.5% healthy British children (CH vs. normal, P < 0.0001). We found that 54.7% children with CH had reached AR compared with 21.4% of normal children (CH vs. normal, P < 0.0001) by the age of 49 months. Timing of AR showed significant negative correlation with BMI SDS at 10 years (r =-0.487, P = 0.01). There were no significant relationships between timing of AR and initial thyroid function or age at normalization of TSH. Multiple logistic regression analysis identified age at AR as an independent factor associated with BMI greater than or equal to 20 at 10 years of age (P = 0.04). CONCLUSIONS Children with CH showed significantly earlier AR compared to normal British children. This showed significant negative correlation with BMI SDS at 10 years. AR in CH does not appear to be directly related to the initial severity of hypothyroidism or to treatment factors.