Infant development could be delayed when supplemental iron is given to infants who don't need it, according to a new study. Too much or too little of this essential nutrient is problematic for infants and children.

In many parts of the world, the amount of iron in infant formula is routinely boosted to avoid iron deficiency anemia and other illnesses. The findings from this study suggest a need to reconsider the call for universal iron supplements.

The extra iron seemed to give a slight boost to kids whose hemoglobin levels were initially low, but was linked to lower scores in kids whose hemoglobin levels were normal.

Iron deficiency is a worldwide public health problem. Iron is a nutrient that's essential to the growth and development of infants and children. It is necessary for healthy red blood cells which move oxygen from the lungs throughout the body and helps the muscles store and use oxygen.

Low iron levels in children can lead to anemia, a condition in which the body does not have enough healthy red blood. Untreated iron deficiency in children can cause physical and mental delays in areas such as walking and talking. Anemic children tend to score lower on tests and be disruptive in the classroom.

Now it appears that children who have too much iron in their blood are also at risk.

The study actually began in 1991 when researchers tested the hemoglobin levels of 835 infants when they were six months old. Those who were not anemic were randomly assigned to a group who received low-iron (2.3 mg/L) or high-iron (12.7mg/L) formula until they were one year old.

Ten years later, nearly 500 of the children in the original study were given a series of thinking, coordination, and memory tests. Comparing the cognitive and visual-motor development of the children who received the high-iron formula to those who received the low-iron formula, those who received the high-iron formula lagged behind.

According to Betsy Lozoff, the study's principal investigator and research professor at the University of Michigan in Ann Arbor, most of the children who received the 12 mg formula did not show lower scores, but the 5 percent with the highest hemoglobin levels at 6 months of age showed the poorest outcome. These children scored 11 points lower in IQ and 12 points lower in visual-motor integration.

Similar scores were observed for spatial memory and eye-hand coordination. The extra iron seemed to give a slight boost to kids whose hemoglobin levels were initially low, but was linked to lower scores in kids whose hemoglobin levels were normal.

The American Academy of Pediatrics' Committee on Nutrition has advocated iron-fortified infant formulas since 1969 as a way of reducing the prevalence of iron-deficiency anemia and its side effects during the first year of life. In the United States, the concentration of iron in iron-fortified formulas ranges from 10 mg per liter to 12 mg per liter.

The researchers caution that the study was based on a very small sample size and most of the infants in the study had normal or low hemoglobin. The ten-year test scores were also not the original focus of the study, and more research needs to be performed before any conclusions can be made about harmful side effects from consuming too much iron through infant formula.

The study was published first online in the Archives of Pediatric and Adolescent Medicine.