Valentina Sivryukova knew her public service messages were hitting the mark when she heard how one Kazakh schoolboy called another stupid. ''What are you,'' he sneered, ''iodine-deficient or something?''
Ms. Sivryukova, president of the national confederation of Kazakh charities, was delighted. It meant that the years spent trying to raise public awareness that iodized salt prevents brain damage in infants were working. If the campaign bore fruit, Kazakhstan's national I.Q. would be safeguarded.
In fact, Kazakhstan has become an example of how even a vast and still-developing nation like this Central Asian country can achieve a remarkable public health success. In 1999, only 29 percent of its households were using iodized salt. Now, 94 percent are. Next year, the United Nations is expected to certify it officially free of iodine deficiency disorders.
That turnabout was not easy. The Kazakh campaign had to overcome widespread suspicion of iodization, common in many places, even though putting iodine in salt, public health experts say, may be the simplest and most cost-effective health measure in the world. Each ton of salt needs about two ounces of potassium iodate, which costs about $1.15.
Worldwide, about two billion people -- a third of the globe -- get too little iodine, including hundreds of millions in India and China. Studies show that iodine deficiency is the leading preventable cause of mental retardation. Even moderate deficiency, especially in pregnant women and infants, lowers intelligence by 10 to 15 I.Q. points, shaving incalculable potential off a nation's development.
The most visible and severe effects -- disabling goiters, cretinism and dwarfism -- affect a tiny minority, usually in mountain villages. But 16 percent of the world's people have at least mild goiter, a swollen thyroid gland in the neck.
''Find me a mother who wouldn't pawn her last blouse to get iodine if she understood how it would affect her fetus,'' said Jack C. S. Ling, chairman of the International Council for Control of Iodine Deficiency Disorders, a committee of about 350 scientists formed in 1985 to champion iodization.
The 1990 World Summit for Children called for the elimination of iodine deficiency by 2000, and the subsequent effort was led by Professor Ling's organization along with Unicef, the World Health Organization, Kiwanis International, the World Bank and the foreign aid agencies of Canada, Australia, the Netherlands, the United States and others.
Largely out of the public eye, they made terrific progress: 25 percent of the world's households consumed iodized salt in 1990. Now, about 66 percent do.
But the effort has been faltering lately. When victory was not achieved by 2005, donor interest began to flag as AIDS, avian flu and other threats got more attention.
And, like all such drives, it cost more than expected. In 1990, the estimated price tag was $75 million -- a bargain compared with, for example, the fight against polio, which has consumed about $4 billion.
Since then, according to David P. Haxton, the iodine council's executive director, about $160 million has been spent, including $80 million from Kiwanis and $15 million from the Gates Foundation, along with unknown amounts spent on new equipment by salt companies.
''Very often, I'll talk to a salt producer at a meeting, and he'll have no idea he had this power in his product,'' Mr. Haxton said. ''He'll say 'Why didn't you tell me? Sure, I'll do it. I would have done it sooner.' ''
In many places, like Japan, people get iodine from seafood, seaweed, vegetables grown in iodine-rich soil or animals that eat grass grown in that soil. But even wealthy nations, including the United States and in Europe, still need to supplement that by iodizing salt.
The cheap part, experts say, is spraying on the iodine. The expense is always for the inevitable public relations battle.
In some nations, iodization becomes tarred as a government plot to poison an essential of life -- salt experts compare it to the furious opposition by 1950s conservatives to fluoridation of American water.