New York - Iodine supplements may improve mental function in children with even mild deficiencies in the nutrient, a small study suggests.

Iodine is a chemical element necessary for normal growth and development of the brain and body. Because the body does not make iodine, it must be obtained from the diet -- from sources like seafood, dairy products, plants grown in iodine-rich soil and iodized table salt.

Severe iodine deficiency has long been known to cause mental impairment, stunted growth and other problems in children. Such deficiency remains a major problem in parts of the world -- typically where the soil is iodine-poor, people eat little seafood and salt is not iodized.

But there has also been a recent re-emergence of milder iodine deficiency in certain countries, including New Zealand and Australia -- thought to be due to factors like declining use of iodized salt and changes in dairy-product manufacturing that have lowered iodine levels.

Whether mild deficiency affects children's mental functioning, and whether the problem should be treated, is still in question.

To study the issue, researchers in New Zealand randomly assigned 184 mildly iodine-deficient children to take either a tablet containing 150 micrograms of iodine or a placebo pill every day for 28 weeks.

At the end of the study, children in iodine group showed an overall improvement on two standard cognitive tests that gauge problem-solving abilities. And they outperformed children who received the placebo.

Iodine is necessary for the body to produce thyroid hormones, which regulate metabolism. The traditional view was that since these hormone levels are still within normal range when a person is mildly iodine deficient, the lack of iodine may have no health effects.

The current findings, however, suggest that mild iodine deficiency "could prevent children from attaining their full intellectual potential," the researchers report in the American Journal of Clinical Nutrition.

Still, it is too soon to start routinely treating children with mild deficiencies, according to Dr. Sheila A. Skeaff, a senior lecturer at the University of Otago in Dunedin and one of the researchers on the work.

"More studies should be done," she told Reuters Health in an email. "We found a small effect in children (and) we don't know if this is permanent or not."

Skeaff pointed out that there are no standard tests for mild iodine deficiency. The best solution for people who think they might be deficient is to regularly eat foods high in iodine and use iodized table salt.

In the U.S., Skeaff noted, most children are not iodine-deficient, as the typical American diet provides adequate levels.


American Journal of Clinical Nutrition, October 2009.