New research shows the intelligence of many kids in the past generation of New Zealand children may have been stunted.
In the first study of its kind, Otago University researchers have now shown that giving children a little more iodine to correct a mild deficiency in their diet measurably boosts their intelligence.
The findings have just been published online by the American Journal of Clinical Nutrition.
Mild iodine deficiency has been an increasing problem in New Zealand over the past two decades and may be preventing children from attaining their full intellectual potential, said researcher Sheila Skeaff.
"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," she said.
Bread manufacturers have until this month to comply with new regulations requiring the use of iodised salt.
Skeaff said salt used in the home should also be iodised.
"Parents should also consider giving children who do not eat commercial breads an iodine-containing multimineral supplement," she said today.
The Government last month rolled over on proposals to add folic acid to bread to reduce the number of babies born with neural tube defects such as spina bifida.
Skeaff, principal investigator at the university's department of human nutrition, said that moderate to severe deficiency of iodine was well-known for its sometimes disastrous effects on children's brain development, which could include cretinism.
But it had previously been thought that being only mildly iodine deficient had no significant consequences for thinking capacity.
"Our findings challenge this assumption," she said.
"They also show that the new era of mandatory fortification of most bread with iodised salt is a good move ... which may reap even greater benefits than initially thought."
Food Standards Australia New Zealand (FSANZ), has reduced the concentration of iodine in iodised salt from 25mg-65mg per kg to 20mg-45mg, but required it to be used in baked cereal products - bread, breakfast foods and biscuits.
Adults required an average of 100 micrograms of iodine a day.
A recent total diet survey showed women over 25 were only getting 40% of that.
Pregnant women need 160 micrograms, and breastfeeding women 190 micrograms and they are likely to still need additional supplements to get sufficient iodine in their diet.
Goitre problems - thyroid enlargement - are typically seen with an intake of less than 50 micrograms of iodine a day and cretinism is seen in severe cases, in the babies of pregnant women who received less than 30 micrograms a day.
Medical experts say women having babies or breastfeeding should take up to 200 micrograms of iodine supplements a day, unless they have thyroid disease or get a lot of iodine from sources such as seafood.
A lack of iodine during the development of a foetus usually means a baby will take iodine from the mother, whose own iodine levels drop further, with potential for a knock-on effect for her next baby to have an even lower reserve of iodine available.
In the Otago study, researchers tested 184 mildly iodine-deficient Dunedin children aged between 10 and 13 over 28 weeks.
Those who received daily iodine tablets improved their performance in a standard intelligence test used for children.
"The iodine group showed a significantly improved performance relative to the placebo group," Skeaff said. But there was no evidence that large doses of iodine would lead to correspondingly larger gains in intelligence.