11 August 2004

A study conducted in Spain published in the August 2004 Journal of Clinical Endocrinology and Metabolism has found a positive relationship between iodine intake and intelligence quotient (IQ) in children between the ages of six and sixteen.

Piedad Santiago-Fernandez, MD, of the Unidad de Endocrinología, Complejo Hospitalario Ciudad de Jaén, and colleagues measured the urinary iodine levels of 1,221 southern European children to determine iodine intake. Dietary questionnaires and IQ tests were completed by all participants. The children were examined for the presence of goiter (a disease caused by iodine deficiency characterized by enlargement of the thyroid gland), and blood samples were analyzed for thyroid hormones.

Goiter was diagnosed in 19.4 percent of the children and was more prevalent in girls than boys. The mean IQ was 97.2 (average IQ is 100). Gender, education level and the presence of goiter had no effect on IQ, but iodine levels greater than 100 micrograms per litre were significantly associated with having a higher IQ. Compared to those whose urinary iodine levels were 150 micrograms per litre or higher, children with levels that were 25 micrograms per litre or less experienced more than double the risk of having an IQ in the lowest 25 percent.

These results suggest that improving dietary iodine intake could enable many children to increase their IQ scores.