Iodine's role in learning.

For decades, physicians have known that extreme iodine deficiency during pregnancy can cause severe mental retardation in developing babies. A study of boys age 9 to 15 now indicates that childhood iodine deficiency can impair not only learning but also motivation to achieve-a barrier to learning not previously associated with this deficiency.

Banarasi D. Tiwari and his coworkers at the Sanjay Gandhi Post Graduate Institute of Medical Sciences in Lucknow, India, focused on 100 boys from villages in eastern India. Though very poor, each child had attended school, where he had learned to read and write. Roughly half of the boys had goiters of varying grades, a sign of severe iodine deficiency.

Compared to boys their age from neighboring villages who had no overt signs of the deficiency, boys from the goiter-prone areas proved slower learners on all tests except the recall of verbally relayed information, Tiwari's group reports in the May American Journal of Clinical Nutrition. Children from the severely deficient communities also improved less after practice drills than did boys from the other villages.

Although children from the more iodine-deficient villages may have suffered some nerve damage during earlier development that continues to affect their ability to learn, Tiwari's team notes that older children often performed more poorly than younger ones-suggesting a cumulative impairment.

The most dramatic difference between the two groups, the Indian scientists report, was a strikingly lower motivation to achieve in those from the most iodine-deficient villages.

"[T]hese abnormalities may prevent millions of children from achieving their full potential, even if learning opportunities are made available," the researchers conclude. Seafood and iodized salt can supply the iodine needed for normal function of the thyroid, whose hormones play an important role in cognition and learning.