Giving impoverished infants iron and zinc supplements to prevent nutritional deficiencies may not have lasting benefits for their mental skills, a new study shows.

The findings, from a study of school-age children in northeastern Thailand, suggest that iron and zinc do not boost their IQ, memory or other intellectual abilities - at least not when the minerals are given only during infancy.

Iron and zinc are important to normal brain development, and children in developing nations are at risk of deficiencies in both minerals.

Some studies have found that giving these children iron and zinc during infancy can improve their blood levels of the nutrients, and possibly help them reach some developmental milestones sooner - like walking on their own.

But little has been known about whether those supplements have lasting benefits.

In the new study, researchers assessed 560 nine-year-olds in Thailand who, as infants, had been randomly assigned to have supplements of iron, zinc, both nutrients, or a placebo (a substance that looked like the real supplements but didn’t contain any nutrients). The infants received the supplements or the placebo for 6 months, starting between the ages of 4 and 6 months.

At the age of 9 years, the children were given a variety of standard tests of their IQ, memory, attention and school performance. Overall, the researchers found no differences in the average test scores of children who had received iron, zinc or the placebo.

But the findings do not necessarily mean that iron and zinc supplements offer no brain benefit to children in the developing world.

“It is too soon to tell,” said senior researcher Dr. Reynaldo Martorell, of Emory University in Atlanta, an author of the report that appears in the American Journal of Clinical Nutrition.

One possibility, Martorell told Reuters Health in an email, is that the supplements need to be started sooner - given to mothers during pregnancy - and continued through at least a child’s first 2 years.

A recent study of schoolchildren in rural Nepal found that when mothers took iron and folic acid during pregnancy, their kids did better on tests of intelligence and fine motor skills.

But it’s also possible, according to Martorell, that iron and zinc, or any two nutrients, are not enough. “Maybe all nutrient intakes need to be improved, not just two,” he said.

“I think the evidence will eventually show that in order to have long-term benefits on (the brain), major deficiencies in early life - such as iron and zinc, but others as well - need to be addressed,” Martorell said.

Still, the researcher added, there are many short-term reasons to ensure that infants and children in the developing world have enough iron and zinc. There is some evidence, for example, that zinc supplements help prevent or treat diarrhea - a major killer of children in poor nations.

Iron supplements can also prevent some cases of anemia, a disorder in which the blood’s oxygen-carrying capacity is reduced - causing problems like fatigue, dizziness and breathlessness.

Few children in the current study had overt iron deficiency as infants, when their supplements were started. But worldwide, iron deficiency is the most common nutritional disorder, affecting 2 billion people, according to the World Health Organization.

SOURCE: American Journal of Clinical Nutrition, online January 26, 2011