Children’s cognitive scores improve after mild iodine deficiency is corrected

Mild iodine deficiency may prevent children from reaching their full intellectual potential, according to groundbreaking new University of Otago research.

In the first study of its kind, Otago researchers have now shown that iodine supplementation to correct the mild deficiency commonly found in New Zealand children leads to small but significant improvements in their performance in cognitive tests. 

The findings have just been published online by the American Journal of Clinical Nutrition, which is the most highly rated journal in the nutrition and dietetics category.

Principal Investigator Dr Sheila Skeaff of the Department of Human Nutrition says that while moderate to severe deficiency of this trace element has well-known and sometimes disastrous effects on children’s brain development, it had previously been thought that being only mildly iodine deficient had no significant cognitive consequences.

"Our findings challenge this assumption," says Dr Skeaff. "They also show that the new era of mandatory fortification of most bread with iodised salt is a good move for New Zealand, which may reap even greater benefits than initially thought."

In the study, researchers from the University’s Departments of Human Nutrition and Psychology undertook a 28-week-long trial involving 184 Dunedin children aged between 10 and 13.

The children, who were found to be mildly iodine deficient at the outset, were randomly assigned to groups which either received daily iodine tablets or a placebo. At the beginning and end of the trial, both groups underwent cognitive testing using four subtests from WISC-IV, which is a standard intelligence test used for children.

By the trial’s end, the researchers found that the children taking the iodine supplement had achieved adequate iodine status, while the placebo group remained mildly deficient.

"In the initial round of cognitive testing, there were no significant differences between the two groups’ scores. When tested again at the end of the trial, in two subtests measuring perceptual reasoning, the iodine group showed a significantly improved performance relative to the placebo group."

Although the score gains were not huge, they still indicate that mild iodine deficiency – which has been an increasing problem in New Zealand over the past two decades – may be preventing children from attaining their full intellectual potential, she says.

"While children eating fortified bread should benefit through improving their iodine status, those who do not eat it should be taking steps to increase their iodine intakes in other ways.

"Although fish and seafood are rich sources of iodine, most New Zealand children eat small quantities of these foods. If salt is used in the home, at the table or in cooking, it should be iodised. Parents should also consider giving children who do not eat commercial breads an iodine-containing multimineral supplement. However, it is important to note that there is no evidence that large doses of iodine will lead to large cognitive gains."

(Source: University of Otago: American Journal of Clinical Nutrition: September 2009)