Author(s):
Carvalho, Irene P. ; Peixoto, Bruno ; Caldas, José Carlos ; Costa, Ana ; Silva, Sofia ; Moreira, Bárbara ; Almeida, Agostinho ; Moreira-Rosário, André ; Guerra, António ; Delerue-Matos, Cristina ; Sintra, Diana ; Pestana, Diogo ; Pinto, Edgar ; Mendes, Francisca Castro ; Martins, Inês ; Leite, João Costa ; Fontoura, Manuel ; Maia, Maria Luz ; Queirós, Pedro ; Moreira, Roxana ; Leal, Sandra ; Norberto, Sónia ; Costa, Vera ; Fernandes, Virgínia Cruz ; Keating, Elisa ; Azevedo, Luís ; Calhau, Conceição
Date: 2022
Persistent ID: http://hdl.handle.net/10400.22/22015
Origin: Repositório Científico do Instituto Politécnico do Porto
Subject(s): Excessive iodine; Cognition; School ages; Iodine-adequate population; Representative sample
Description
The goal of this work was to examine whether elevated iodine intake was associated with adverse effects on IQ among school-age children in Portugal. In a representative sample of children from the north of the country, IQ percentiles by age (assessed with Raven’s Colored Progressive Matrices) were dichotomized to <50 (“below-average” IQs) and ≥50. Morning urine iodine concentrations, corrected for creatinine, were dichotomized to <250 µg/g and ≥250 µg/g, according to the European Commission/Scientific Committee on Food’s tolerable upper level of daily iodine intake for young children. Data were examined with Chi-square tests, logistic regression, and GLM univariate analysis. The sample (N = 1965) was classified as generally iodine-adequate (median urinary iodine concentration = 129 µg/L; median iodine-to-creatinine ratio = 126 µg/g) according to the WHO’s criteria. A greater proportion of children in the ≥250 µg/g group had below-average IQs, compared to children with less than 250 µg/g (p = 0.037), despite a sizable (though non-significant) proportion of children in the less-than-250 µg/g group also presenting below-average IQs, at the bottom of the iodine distribution (<50 µg/g). The proportion of below-average IQs increased with increasingly elevated iodine concentrations (p = 0.047). The association remained significant after the adjustment for confounders, with the elevated iodine group showing increased odds of having below-average IQs when compared with the non-elevated iodine group (OR 1.55; 95% CI 1.11–2.17; p = 0.011). Consistently, the former group presented a lower mean IQ than the latter (p = 0.006). High iodine intake was associated with lower IQs even in a population classified as iodine-adequate. These results bear on child cognition and on initiatives involving iodine supplementation
