Intelligence quotient and iodine intake: a cross-sectional study in children

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 microg/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 microg/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 microg/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 microg/liter.