The infant formulas currently available in the United States are either "iron-fortified"--with approximately 12 milligrams of iron per liter--or "low iron"--with approximately 2 milligrams of iron per liter.
"There should not be a low-iron formula on the market for the average child because a low-iron formula is a nutritionally deficient formula," says Klish. "It doesn't provide enough iron to maintain proper blood cell counts or proper hemoglobin." (Hemoglobin is a blood protein that carries oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs.)
In addition, studies have shown that school children who had good iron status as infants because they were fed iron-fortified formula performed better on standardized developmental tests than children with poor iron status. However, Wallingford says that "FDA has permitted marketing of low-iron formulas because some pediatricians prefer to use them, with the caveat that the physician would be monitoring iron status and prescribing iron supplements when appropriate."
Why is there low-iron formula on the market? "In the past there have been a lot of symptoms that have been attributed to iron, including abdominal discomfort, constipation, diarrhea, colic, and irritability," says Klish. "Also there was some concern about too much iron interfering with the immune system. All of those concerns and questions have been laid to rest with appropriate studies."
Another reason for originally producing low-iron formulas was that human milk contains low amounts of iron--less than a milligram per liter. However, it is now understood that an infant absorbs virtually 100 percent of the iron from human milk, but considerably less from infant formula.
Researchers continue to try to determine the best amount of iron for infant formula. While low-iron formulas don't supply enough iron, the best amount of iron for formulas has not been established. "We did not have much data at the time the regulations were written for different intake levels of iron," says Wallingford. He explains that the current amounts give good developmental results, "but, based on European experience, half [of the high level] is probably good enough to do the same thing." Currently, the Federation of American Societies for Experimental Biology is evaluating what the best levels may be and will make recommendations to FDA on what levels of iron to require in formulas. The study is also reviewing the level of all other nutrients in infant formula, as well as the need for nutrients not currently included.
