Infant formula ingredient studied in rats

Last Updated: 2002-10-07 17:00:39 -0400 (Reuters Health)

By Suzanne Rostler

NEW YORK (Reuters Health) - Scientists have found that newborn rats fed a mineral found in higher levels in infant formula--especially soy formula--than in breast milk may have attention-related changes in a brain chemical.

However, the preliminary findings need to be confirmed in larger studies before it is known if the mineral--manganese--has any link to behavioral problems in children.

Breast milk contains 4-6 micrograms per liter (mcg/L) of manganese, while milk-based infant formula contains about 30-50 mcg/L and soy formula contains 200-300 mcg/L. Manganese is a mineral that helps the cells to obtain energy and it is essential for life, but can be toxic at very high levels.

"Very little is actually known about the association between manganese and ADHD specifically," said Dr. James Perrin, a professor of pediatrics at Harvard Medical School and co-chairman of the American Academy of Pediatrics subcommittee on attention-deficit/hyperactivity disorder (ADHD). "It's too soon to worry."

The American Academy of Pediatrics recommends that infants who are not breast-fed receive infant formula fortified with iron, either soy- or cow's milk-based.

The study, led by Dr. Francis Crinella from the University of California, Irvine, included 32 newborn rats that were fed 0 to 500 micrograms of manganese daily. The amounts given to rats were designed to mimic the amounts in breast-fed and formula-fed infants.

There was no difference between rats fed low doses of manganese and those given none of the mineral, but the highest doses of manganese were associated with lower levels of dopamine, a brain chemical involved in problem-solving tasks, according to the report in a recent issue of NeuroToxicology.

The adult rats that had been fed higher doses of manganese also seemed to have slightly more problems completing tasks and altering certain behaviors, but the results did not reach statistical significance, and may have been a chance finding.

The researchers studied manganese because past research in manganese miners have shown that exposure to extremely high doses of the mineral can lead to a condition similar to Parkinson's disease that is marked by tremors and other neurological symptoms.

In an interview with Reuters Health, Crinella cautioned that rats were given a manganese supplement and not soy formula per se.

"We are worried about soy formula because it contains approximately 80 times the manganese level of human breast milk, but there may be other minerals present in the formula that could offset the toxic effects," he said, noting that he is currently conducting studies on primates.

"Unlike the rat that must have breast milk for survival, the primate can be bottle fed with soy formula from birth," he explained.

Iron and the calcium in milk are known to protect against manganese toxicity, according to the report.

Dr. Mary Beth Arensberg, director of public affairs with Ross Products, said manganese levels in soy infant formula reflect those found in the protein sources used to make the formula and fall within the range recommended by experts. She also notes that infants have consumed such formulas safely for decades.

"Soy formulas are safe and an important feeding option for infants. It has been fed to millions of infants for more than 60 years (in the US)," Arensberg said. Infants in Asia have received soy-based nutrition for centuries.

Ross Products is the division of Abbott Laboratories that manufactures the soy-based formula, Isomil. ProSobee, another soy-based formula, is manufactured by Mead Johnson Nutritionals.

SOURCE: NeuroToxicology 2002;145:1-7.

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