A study of school-age children in northeastern Thailand suggests that iron and zinc do not boost their IQ, memory or other intellectual abilities 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 deficiency of 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.
Until now, little has been known about whether those supplements have lasting benefits.
However, 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, one of the authors of the report that appears in the American Journal of Clinical Nutrition.
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.