Abstract

Objective: Thyroid hormones (THs) are crucial for the correct maturation of the CNS and the neurodevelopment of the child. We aimed to investigate the association of TSH and free thyroxine (FT4) levels with cognitive functioning in children from the INMA-Granada cohort studied during their follow-up at the age of 9-11 years. Design: We evaluated 300 children from the original cohort, which comprised 668 eligible mother-son pairs recruited at birth from 2000 to 2002 in Granada (Spain). Methods: FT4 and TSH concentrations were measured, and cognitive development was assessed using neuropsychological tests (n = 187). Children with chronic disease related to thyroid function and/or cognitive development were excluded. Results: Median TSH and FT4 levels were 3.1 mu IU/ml and 1.2 ng/dl respectively. In multivariable regression analyses adjusted for maternal and child characteristics, children with TSH levels in the top tertile had worse verbal comprehension and immediate and long-term recall. Children with FT4 levels in the top tertile had better attention and lower impulsivity and were at a lower risk of scoring below the 20th percentile in intelligence quotient (OR=0.24; 95% CI=0.08-0.74; P=0.013) and in abstract reasoning ability (OR=0.28; 95% CI=0.09-0.88; P=0.029). Conclusion: Our findings indicate that circulating THs and TSH may in the top tertile have an impact on cognitive functions; thus, higher TSH slightly but significantly increased the risk of a lower score in certain neuropsychological tests.