Feeding soy-based formulas that contain genistein to infants may reduce a baby’s susceptibility to sometimes-deadly rotavirus infections by as much as 74%, according to a study published in September’s Journal of Nutrition (“Isoflavones at Concentrations Present in Soy Infant Formula Inhibit Rotavirus Infection in Vitro,” by Aline Andres, Sharon M. Donovan, Theresa B. Kuhlenschmidt and Mark S. Kuhlenschmidt). According to the study authors, this is the first study showing the inhibition of rotavirus infectivity by isoflavones present in soy formula.
“Rotavirus is the primary cause of diarrhea in infants, affecting virtually all children before age five,” says Donovan, the Melissa M. Noel Professor of Nutrition, University of Illinois, Urbana. “In the United States, it mainly leads to dehydration, doctor’s visits, and parents missing work to care for sick children. In developing countries, though, rotavirus causes approximately 611,000 deaths each year.
In the study, cells in culture were exposed to rotavirus in the absence or presence of soy isoflavones. Each different form of soy isoflavones were tested individually and as the complete mixture present in infant formula. Genistein and the mixture significantly reduced rotavirus infections by 33% to 74% compared to the control and when exposed to a variety of virus concentrations. Removing the genistein caused the mixture to lose its anti-rotavirus activity, suggesting that it is the active component.
The study examined the isoflavone concentrations present in soy formula. At that concentration rotavirus inhibition began to occur and then leveled off, indicating the effective range, and that, beyond that range, no additional inhibition or toxicity occurs. Researchers theorize that genistein may diminish infectivity by inhibiting the ability of the rotavirus to bind to tissue-culture cells.
Genistein is a phytoestrogen--a nonsteroidal, estrogenic compound that occurs naturally in plants--found in significant levels in soybeans. The safety of soy infant formulas has been called into question in recent years due to possible negative effects of this phytoestrogen on human development. However, in March 2006, the Center for the Evaluation of Risks to Human Reproduction, a part of the National Institutes of Health, called together a panel of 14 scientific experts to examine soy formula and genistein. The panel reviewed and evaluated scientific research and concluded little or no concern about soy formula existed. Total genistein intake of infants using soy formula is 8 milligrams per kilogram or less, considerably below the 35 mg or higher levels that may cause problems.
Approximately 10% to 20% of all infants in the United States consume soy formula. Although rotavirus vaccines are now available, they are expensive and cannot be given to some infants.
“It’s exciting to think that the isoflavones in soy formula could be a cost-effective nutritional approach to decreasing the incidence and severity of rotavirus infections, especially among children in developing countries who are most at risk,” says Donovan.
The study was funded by the USDA and the Illinois Soybean Association.
