Urinary iodine concentrations in preschoolers and cognitive development at 4 and 6 years of age, the Rhea mother-child cohort on Crete, Greece

Background

Evidence regarding child iodine intake and neurodevelopment is scarce.

Methods

We aimed to assess the impact of child iodine intake at 4 years of age on cognitive and motor development at 4 and 6 years among 304 children from the Rhea cohort on Crete, Greece. Child iodine intake was assessed via urinary iodine concentrations (UIC) measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and adjusted for specific gravity. Child cognitive and motor development was assessed using the McCarthy Scales of Children's Abilities (MSCA) at 4 years of age and Raven’s Coloured Progressive Matrices (RCPM), Finger Tapping Test (FTT), and Trail Making Test (TMT) at 6 years. Associations were explored using multivariable-adjusted linear regression analyses with UIC categorized according to WHO criteria [insufficient intake <100 µg/L, adequate 100–299 µg/L (reference group), excessive ≥300 µg/L].

Results

The children’s median UIC was 249 µg/L (25–75th percentile: 181–344 μg/L). Children with UIC <100 μg/L had lower scores in the motor scale at 4 years (MSCA-motor scale: B=-10.3; 95 %CI −19.9, −0.6; n=10) and in intelligence at 6 years (RCPM-total score: B=-3.6, 95 %CI −6.8, −0.5; n=9) than children in the reference group. No associations were found with the general cognitive scale at 4 years or with TMT and FTT scales at 6 years. Children with UIC ≥300 μg/L had lower cognitive scores both at 4 (MSCA; B= −3.5; 95 %CI −6.9, −0.1; n =101) and 6 years of age (RCPM-total score; B= −1.2; 95 %CI −2.3, −0.0; n =98) than children in the reference group. No associations were observed with the motor scale at 4 years or with TMT and FTT scales at 6 years.

Conclusion

Our findings indicate that both low and excessive iodine intake at preschool age may adversely affect child cognitive abilities. Additionally, low iodine intake may also impact motor abilities.