For years iron supplements have been given to low weight babies to reduce the long term effects of too little iron in the baby’s blood. A new Swedish study suggests that babies born in the mid-weight range can also benefit from iron supplementation.Babies at the higher end of the low-birth-weight spectrum are at risk of iron deficiency, and should get iron supplements, according to a Swedish study published Monday in Pediatrics.

These "marginally" low-birth-weight infants tip the scales at 4 pounds, 6-8 ounces when born. They represent a large percentage of newborns; for example, 5 percent of babies born in the US every year are in the marginally low-birth-weight range.

While iron supplements are recommended for all low-birth-weight babies, these recommendations aren't always followed for the infants who fall into the marginal range, Dr. Magnus Domellof of Umea University in Sweden told Reuters Health. There is "large variation between different clinics and different hospitals, and there is a lack of guidelines."

Iron deficiency can have a serious impact on a child’s neurological development, but giving too much iron may also be harmful.

To investigate the effects of iron supplementation, Dr. Domellof and his colleagues randomly assigned 285 healthy, marginally low-birth-weight babies to receive either a placebo, or 1 milligram of iron per kilogram of body weight, or 2 milligrams of iron per kilogram, every day between 6 weeks and 6 months of age.

At six months, the researchers found, 36 percent of children in the placebo group were iron deficient, compared to only 8 percent of the 1-mg group and 4 percent of the 2-mg group.

The most severe deficiency, or anemia, was seen in 10 percent of the group given only the placebo.

Eighteen percent of the exclusively breastfed babies in the placebo group had iron deficiency anemia.

Dr. Domellof and his colleagues saw no adverse effects of iron supplementation in any of the infants.

Full-term, healthy babies born to well-nourished mothers have adequate stores of iron in their bodies to carry them through their first 6 months of life. For this reason, they can thrive on breast milk, which contains very little iron, and then begin eating iron-rich solid foods at 6 months of age. But smaller babies have lower reserves, and need to start iron supplementation earlier.

Based on the findings, the researchers conclude that marginally low-birth-weight infants should receive iron supplements from 6 weeks to 6 months of age.

Dr. Domellof, and his colleagues, plan to follow the children up to age seven to determine whether iron deficiency -- or iron supplementation -- has long-term effects on health and development.

Parents should discuss iron deficiency with their Pediatrician before starting their baby on an iron supplementation program.