Iodine supplements improve mental function in children with even mild iodine deficiency.

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 iodised 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 iodised. But there has also been a recent re-emergence of milder iodine deficiency in certain countries thought to be due to factors like declining use of iodised 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 randomly assigned 184 mildly iodine-deficient children in New Zealand to take either a tablet containing 150 micrograms of iodine or a placebo pill every day for 28 weeks.

It was found that at the end of the study, children in the iodine group showed an overall improvement on two standard intelligence tests that gauged 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. Still, it is too soon to start routinely treating children with mild deficiencies.

Therefore the researchers suggested that further studies are needed. 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 iodised table salt.