Association between Elevated Iodine Intake and IQ among School Children in Portugal

Autores da FMUP

• Andreia Filipa Gomes Da Costa

  Autor

• Alexandre Rui Rodrigues Almeida

  Autor

• Maria Isabel Torres Martins

  Autor

• Elisa Oliveira Braga Keating

  Autor

• Luís Filipe Ribeiro De Azevedo

  Autor

• Maria Da Conceição Costa Pinho Calhau

  Autor

Participantes de fora da FMUP

• Carvalho, I.
• Peixoto, B
• Caldas, JC
• Silva, S
• Moreira, B
• Moreira Rosario, A
• Guerra, A
• Delerue Matos, C
• Sintra, D
• Pestana, D
• Pinto, E
• Mendes, FC
• Leite, JC
• Fontoura, M
• Maia, ML
• Queiros, P
• Moreira, R
• Leal, S
• Norberto, S
• Costa, V
• Fernandes, VC

Unidades de investigação

• Biomedicina

• Cirurgia e Fisiologia

• Laboratório Associado RISE- Rede de Investigação em Saúde

  

  Investigador

  Fernando Carlos De Landér Schmitt

• Medicina da Comunidade, Informação e Decisão em Saúde

• Neurociências Clínicas e Saúde Mental

• RISE-Health

  

  Investigador

  Fernando Carlos De Landér Schmitt

Abstract

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 Ravens Colored Progressive Matrices) were dichotomized to <50 (below-average IQs) and >= 50. Morning urine iodine concentrations, corrected for creatinine, were dichotomized to <250 mu g/g and >= 250 mu g/g, according to the European Commission/Scientific Committee on Foods 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 mu g/L; median iodine-to-creatinine ratio = 126 mu g/g) according to the WHOs criteria. A greater proportion of children in the >= 250 mu g/g group had below-average IQs, compared to children with less than 250 mu g/g (p = 0.037), despite a sizable (though non-significant) proportion of children in the less-than-250 mu g/g group also presenting below-average IQs, at the bottom of the iodine distribution (<50 mu g/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.

Keywords

• excessive iodine; cognition; school ages; iodine-adequate population; representative sample