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Inadequate Iodine Intake Linked to Low Intelligence Quotient

  • Authors: News Author: Laurie Barclay, MD
    CME Author: Désirée Lie, MD, MSEd
  • CME Released: 8/9/2004
  • Valid for credit through: 8/9/2005
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Target Audience and Goal Statement

This article is intended for primary care physicians, community physicians, and specialists who care for children.

The goal of this activity is to provide the latest medical news to physicians and other healthcare professionals in order to enhance patient care.

Upon completion of this activity, participants will be able to:

  • List the potential consequences of iodine deficiency in children.
  • Relate urinary iodine levels and dietary intake with IQ in children.


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  • Laurie Barclay, MD

    Laurie Barclay is a freelance reviewer and writer for Medscape.


    Disclosure: Dr. Barclay has reported no significant financial interests.


  • Gary Vogin, MD

    Senior Medical Editor, Medscape


    Disclosure: Dr. Vogin has reported no significant financial interests.

CME Author(s)

  • Désirée Lie, MD, MSEd

    Clinical Professor of Family Medicine; Director, Division of Faculty Development, University of California, Irvine School of Medicine, Irvine, California


    Disclosure: Dr. Lie has reported no significant financial interests.

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Inadequate Iodine Intake Linked to Low Intelligence Quotient

Authors: News Author: Laurie Barclay, MD CME Author: Désirée Lie, MD, MSEdFaculty and Disclosures

CME Released: 8/9/2004

Valid for credit through: 8/9/2005



Aug. 9, 2004 — Inadequate iodine intake is associated with low intelligence quotient (IQ), according to the results of a cross-sectional survey published in the August issue of The Journal of Clinical Endocrinology & Metabolism. The investigators recommend a urinary output of more than 150 μg/L vs lower output may be associated with higher IQ.

"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," write Piedad Santiago-Fernandez, MD, from the Unidad de Endocrinología, Complejo Hospitalario Ciudad de Jaén in Spain, and colleagues. "Studies of the effect of iodine administration on psychomotor development are not consistent. Some have shown iodine supplements to be beneficial in children aged 6-8 years, whereas others have found no benefit in children aged 5-12 years."

In this study, 1,221 schoolchildren from southern Europe had measurement of urinary iodine levels and completed a questionnaire about their usual dietary habits. Median urinary iodine output was 90 µg/L.

IQ, measured by Cattell's g factor test, was significantly higher in children with urinary iodine levels above 100 µg/L. Children with urinary iodine levels less than 100 µg/L had a greater risk of having an IQ below 70. Risk factors for having an IQ below the 25th percentile were consumption of noniodized salt and drinking milk less than once daily.

"This study demonstrates that the IQ of schoolchildren in a developed country can be influenced by iodine intake," the authors write. "Although this was not an interventional study, the results suggest that an increase in dietary iodine to raise median urinary iodine output above 150 µg/liter would enable the IQ to be increased several points in many of these children."

Goiter was twice as common in girls as in boys, suggesting that unless these girls improve their iodine intake, they would be unable to fulfill their iodine requirements should they become pregnant.

"This might well have a negative effect on the neurodevelopment of the unborn child during the first half of gestation, leading to potentially irreversible damage," the authors conclude.

The Junta de Andalucía and Maimónides Association supported this study.

J Clin Endocrinol Metabol. 2004;89:3851-3857