Iodine deficiency affects over a quarter of world population.

Despite huge gains in programs that add iodine to food, some 1.6 billion people remain vulnerable to a range of crippling health problems because their diets do not contain enough of this essential element, according to the World Health Organization (WHO). One-third of these people live in Asia; just last year, 35 to 65 percent of the newborns tested in the provincial capitals of China showed iodine deficiencies.

Lack of iodine in the early stages of life impairs the development of the brain and certain other organs. Severe fetal iodine deficiency can cause cretinism, a condition that involves severe mental retardation and a stunted physique. Even a mild deficiency in early childhood can compromise intelligence; IQ tests have shown a 10 to 15 percent drop in expected scores among children with iodine-poor diets. The problem may also manifest itself in the deformity known as goiter - an enlargement of the thyroid gland, located at the base of the neck.

Although only a small amount of iodine is necessary for human health, many communities lack a source of the element in their local food supply. Coastal populations can often get their iodine from fish, but for people living in mountainous and flood-prone regions, meeting the dietary requirement can be harder because water run-off tends to leach iodine out of the soil. And some foods, such as cassava (a root crop grown throughout much of the tropics), actually inhibit absorption of the element.

Most countries facing widespread iodine deficiency have programs for distributing iodized salt, an approach supported by WHO, UNICEF, and the International Council for the Control of Iodine Deficiency Disorders, a research and development NGO that is a leading authority in the field. Salt is an easily distributed commodity and the cost of adding iodine to it comes to less than $0.10 per person per year. In some countries, other readily distributed foods are used for iodization; Australia, for instance, uses bread and Thailand uses fish paste. In parts of Asia and Africa, iodine is introduced directly into drinking water sources.

But ignorance can be as great a problem as lack of iodine itself. A 1991 survey in Cameroon, for example, found that one-third of the people questioned believed that goiter was the result of sorcery. Iodized salt was available in Cameroon, but there was no clear understanding of the importance of using it.

To deal with such problems, several countries have incorporated an educational element into their iodine campaigns. Indonesia, for example, saw its 1992 iodine plan stagnate due to lack of interest and enforcement. But today, Indonesian schools explain the importance of consuming iodized salt, and test salt samples from pupils' homes. The country even created a television advertising campaign that spotlighted the link between iodine and intelligence. Public awareness campaigns are also helping in Pakistan, where 70 percent of the population is believed to be at risk for iodine deficiency. The government launched a publicity campaign in 1994, with the help of UNICEF and other organizations; since then, 35 million Pakistanis, or about a quarter of the population, have started using iodized salt. Although programs such as these probably include some people who were already getting sufficient iodine, the message is clearly beginning to resonate widely: according to a report released by UNICEF last June, 1.5 billion more people were using iodized salt in 1995 than in 1990.

But progress can be readily undone. A 1992 conference concluded that the problem had returned to Europe, where it was affecting some of the continent's richest and poorest societies. Participants reported that in Croatia, looser regulations have allowed farmers to buy less expensive, non-iodized salt for their livestock - a practice that allowed health problems to resurface in areas dependent upon dairy products for iodine. Iodine deficiences had also reemerged in the Netherlands, where an interest in healthier diets led many people to reduce their consumption of iodized salt and bread. As with so many public health issues, preventing iodine deficiencies is an effort in continual education.