Study: Soy Formula Is Safe

Aug. 14, 2001 -- Everyone would agree that breastfeeding is best for baby, but what if that is not an option?

After making the decision to replace or supplement breastfeeding, parents find themselves in the midst of a long-running and often heated debate — Which is better? Cow milk or soy formula?

In an article appearing in this week's Journal of the American Medical Association, researchers at the University of Pennsylvania's Center for Clinical Epidemiology and Biostatistics find no apparent long-term positive or negative effects of feeding infants soy versus cow milk formula.

There has been much speculation as to whether soy formula, derived from soybeans and high in phytoestrogens, a natural estrogen found in some plants, is safe, in infancy and later in life.

In the United States, an estimated 750,000 infants are given soy formulas each year — 20 percent of the infant population. It has been suggested that giving infants soy formula could accelerate puberty and cause developmental and reproductive abnormalities and thyroid disorders.

Products Called 'Remarkably Safe'

After surveying adults given soy versus cow milk formulas in infancy, researchers at the University of Pennsylvania found little scientific evidence linking health problems to soy formula.

"We found the widely used products are remarkably safe," noted the lead author of the study Dr. Brian Strom, professor and chair of the Center for Clinical Epidemiology and Biostatistics at the University of Pennsylvania.

The study surveyed 811 participants who, as infants, were fed either soy or cow milk formula. Researchers evaluated the subjects, ranging in age of 20-34, and looked at more than 30 medical conditions, including various types of cancer, thyroid conditions, reproductive development, history, and difficulties, as well as general physical development and education levels.

The results showed no higher incidences of the conditions considered in either group. The study did find, however, that women who were given soy as infants had slightly longer and more uncomfortable menstrual periods. But Strom attributes the elevated numbers to statistical chance.

"We don't believe this is biologic," he said. "If it were biologic we'd expect to see higher incidences of other estrogen-based conditions." The research team suggests exploring these findings in future studies.

Reassuring Mom and Dad

Dr. Nancy Krebs, associate professor, University of Colorado School of Medicine, Department of Pediatrics and chair of the American Academy of Pediatrics Committee of Nutrition, is pleased with the results.

"Parents can be reassured," she said "There has been a lot of discussion recently and so far there is no evidence in humans of long-term effects of soy. At this point, the data is very reassuring. There is no reason for the American Academy of Pediatrics to change its [feeding] recommendations."

Although the results are encouraging through the subject's early 30s, this study does not give any indication as to whether differences will develop between the groups as they age. Strom suggests a follow up study in 10-15 years may be needed.