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Intelligence Quotient and Iodine Intake: A Cross-Sectional Study in Children

Unidad de Endocrinología, Complejo Hospitalario Ciudad de Jaén (P.S.-F.), 23007 Jaén, Spain; Departamento de Psicología, Universidad de Jaén (R.T.-B., J.A.M.-M., A.G.L.), 23071 Jaén, Spain; and Servicio de Endocrinología y Nutrición, Complejo Hospitalario Carlos Haya (G.R.-M., E.G.-F., M.J.G., F.S.), 29009 Málaga, Spain

Address all correspondence and requests for reprints to: Dr. F. Soriguer, Servicio de Endocrinología y Nutrición, Hospital Civil, Complejo Hospitalario Carlos Haya, Plaza del Hospital Civil s/n, 29009 Málaga, Spain. E-mail: federico.soriguer.sspa{at}juntadeandalucia.es.

The association between iodine deficiency and poor mental and psychomotor development is known. However, most studies were undertaken in areas of very low iodine intake. We investigated whether a similar association is found in schoolchildren from southern Europe with a median urinary iodine output of 90 µg/liter. Urinary iodine levels were measured in 1221 children who also completed a questionnaire about their usual dietary habits. Intelligence quotient (IQ) was measured by Cattell’s g factor test. IQ was significantly higher in children with urinary iodine levels above 100 µg/liter. The risk of having an IQ below the 25th percentile was significantly related to the intake of noniodized salt and drinking milk less than once a day. As expected, the risk of having an IQ below 70 was greater in children with urinary iodine levels less than 100 µg/liter. In conclusion, this study demonstrates that the IQ of schoolchildren in a developed country can be influenced by iodine intake. The results support the possibility of improving the IQ of many children from areas with mild iodine deficiency by ensuring an iodine intake sufficient to achieve a urinary iodine concentration greater than 100 µg/liter.

This work was supported in part by a grant from the Junta de Andalucía (SAS 124/02) and funds from the Maimónides Association. The investigation group belongs to the Red de Centros de Metabolismo y Nutrición (RCMN, C03/08) of the Instituto de Salud Carlos III.

Abbreviations: CI, Confidence interval; FT3, free T₃; FT4, free T₄; IQ, intelligence quotient; OR, odds ratio; TPO, antithyroperoxidase antibody.

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