Giving underweight babies iron supplements may reduce their risk of behavioral problems later in life, a new Swedish study has found.

The study found that low-birth-weight babies who did not receive iron supplements were 4.5 times more likely to show signs of behavioral problems at age 3 compared with low-birth-weight babies who received iron supplements during early infancy. There was no difference in IQ between the groups.

Babies of low birth weight, defined as weighing less than 5.5 pounds (2,500 grams), are known to be at risk for behavioral problems as well as iron deficiency, a condition that itself has been linked to behavioral problems.

The results suggest that this risk of behavioral problems may be partially prevented with iron supplements, the researchers said.

The findings support the current recommendation to provide iron supplements to low-birth-weight babies starting at 1 month of age, said Dr. David Mendez, a neonatologist at Miami Children's Hospital, who was not involved in the study. Low-birth-weight babies grow rapidly and may not have received enough iron from their mothers in utero to last them during the first few months of life.

Healthy babies should also receive iron supplements starting at 4 months of age if they are breastfed, according to the American Academy of Pediatrics. (Formula contains iron, and healthy babies who are exclusively formula fed will receive enough iron this way.)

Because the study was conducted in Sweden, and most of the babies were breastfed, Mendez said he would like to see the study replicated in different populations to confirm the effect seen on behavior problems.

Because it's possible to give a baby too much iron, it's important for parents to speak with their pediatrician about iron supplementation, Mendez said.

Low birth weight babies

While iron supplements are recommended for low-birth-weight infants, the long-term health effects of this advice have not been rigorously studied. In addition, some studies suggest that too much iron may linked to health risks, such as impaired cognitive development. And the specific risks and benefits of iron supplements for babies who are marginally low birth weight — between 4.4 to 5.5 pounds — have not been studied much at all.

The new study included 285 babies of marginal low birth weight who were randomly assigned to receive a placebo (no iron) or a daily dose of iron (either 1 mg/kg or 2 mg/kg per day) between 6 weeks and 6 months of age. The parents were not told to which group they had been assigned. As far as the researchers knew, the parents could not tell whether their baby had received the supplement or the placebo, said study researcher Dr. Staffan Berglund of Umeå University in Sweden.

When the babies were 3.5 years old, they were given tests to assess their intelligence and behavior. The results were also compared with those of 95 children who had a healthy birth weight.

Signs of behavioral problems, including attention problems, were seen in 12.7 percent of children who did not receive iron supplements. By contrast, only about 3 percent of children who received an iron supplement and 3 percent of children in the healthy weight group showed signs of behavioral problems.

Of the 19 babies with signs of behavioral problems, 15 had an iron intake of less than 1 mg/kg per day.

The results held regardless of whether or not the babies were breastfed or formula fed. However, the researchers caution that because the study was small, they could not rule out the possibility that iron provided by exclusive formula feeding could have affected their results. But many of the babies were at least partially breastfed for up to six months.

Iron and the brain

“In some ways [the findings are] not surprising because we know iron is an important micronutrient in the diet of very young children,” said Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Steven & Alexandra Cohen Children's Medical Center of New York. In animal studies, iron has been shown to be essential for brain cell development.

The behavior assessment used in the study could not diagnose behavioral problems by itself, so additional evaluations are needed, Adesman said. The results would also have been stronger if teacher assessments had been included, he said.

Mendez noted that iron has a bad taste, and it is often hard to get babies to take supplements every day. In fact, 23 percent of children in the study had poor compliance, meaning that less than 70 percent of the supplement doses were given. This is another reason to replicate the study, Mendez said.

The study is published today (Dec. 10) in the journal Pediatrics.

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