To fight the problem, the United Nations is prescribing a whole pantry of artificially fortified foods: soy sauce laced with zinc, "super salt" spiked with iron, cooking oil fortified with vitamin A.
Deficiencies in these vitamins are having alarming effects in developing countries, even ones where people generally have enough to eat, said the study, released Wednesday.
A lack of iron lowers children's IQs by an average five to seven points, the report said. A deficiency in iodine cuts it 13 more points, said Venkatesh Mannar, president of the Micronutrient Initiative, which produced the report along with the United Nations Children's Fund. Birth defects increase when mothers don't get enough folic acid, and a shortage of vitamin A makes children 25-30 percent more likely to die of disease.
"So ubiquitous is vitamin and mineral deficiency that it debilitates in some significant degree the energies, intellects, and economic prospects of nations," the study said.
It looked at 80 developing countries representing some 80 percent of the world's population. It found:
In most Western countries, governments have fought the problem with additives: iodine is sprayed onto salt before packaging, vitamin A is added to milk and margarine, and flour is enriched with niacin, iron and folic acid.
But that doesn't work in countries where governments are weak, food is not processed in big mills and diets are based on a single starchy staple like rice or corn.
Other health experts said the U.N. findings echoed other studies showing the link between intelligence and nutrition.
"This is absolutely happening," said Ronald Waldman, a professor of clinical health at Columbia University. "Vitamin deficiency is a disease, and when people have this disease they don't reach their ideal mental potential."
While some deficiencies, like lack of vitamin A, can be corrected, "If you grow up and your IQ has suffered from iodine deficiency, it's not going to be reversible," Waldman said.
Furthermore, things are getting worse in some countries, the report said. The percentage of salt that is iodized has slipped to 25 percent in some Central Asian countries and to 50 percent in India, the country with the largest number of iodine deficient people, the report said.
Getting vitamins to people other ways just doesn't work, researchers said. In the United States, most people ignored government pleas to take more folic acid, a nutrient found in nuts - until the government started putting it in flour in 1998. The result: cases of spina bifida and anencephaly, two serious birth defects, dropped by at least 20 percent.
"It becomes an issue of compliance. If people have to eat a vitamin pill every day, a lot of them won't do it," Mannar said.
The report urges countries to step up enrichment in foods that people don't make themselves - things like soy sauce, cooking oil or margarine. It also endorses a new kind of salt fortified with iron in "microcapsules."
Putting more nutrients into the food has a measurable economic effect, Mannar said. He cited an Indian study that showed a 20 percent increase in production among tea leaf pickers after iron was added to their diets.
But the most disturbing gap between countries with good and poor nutrition is in intelligence, said Cutberto Garza, a Cornell University professor who also leads the nutrition program at United Nations University.
"A difference of five to seven IQ points doesn't sound like a lot, but you have to look at the tail ends of the (statistical) curve," Garza said. "You are significantly reducing the number of gifted people and increasing the number of people with mental incapacities."
By Chris Hawley