Genistein May Adversely Impact Thymic Function

Genistein May Adversely Impact Thymic Function

URBANA, Ill.--Genistein, a component of soy, caused thymusglands in lab mice to shrink by 50 percent, according to a study at theUniversity of Illinois, Urbana, and published in the Proceedings of theNational Academy of Sciences (www.pnas.org).Researchers, led by Paul S. Cooke, Ph.D., found that giving genistein to labmice whose ovaries had been removed caused a decrease in thymic weight by asmuch as 80 percent. Additionally, thymocyte--a thymic lymphocyte involved inimmune function--numbers were decreased by as much as 86 percent, andT-cells--white blood cells that are critical to fighting off infections--werealso significantly decreased.

Genistein, an isoflavone with estrogenic effects, has been thought to affecthuman female reproductive systems and sexual development in children raised onsoy-based formula, but researchers have not established a link between genisteinand improper development or abnormalities. "We fed levels that weredesigned to basically produce blood levels in the animal that were close orcomparable to what soy-fed human infants have," Cooke said.

So while the results suggest that soy-fed infants may be at risk for thymicor immune system abnormalities, the study is not enough to cause panic. "Ifyou see an effect in mice, that doesn't mean you'll see one in humans,"Cooke said. "If you don't see an effect in mice, that doesn't mean youmight not see one in humans. We're showing nothing related to humans here."

The soy industry quickly rushed to defend soy-based formula. "Thesoy-based infant formula industry has worked to ensure that these products arecontinually evaluated in the population in which they're consumed," saidNancy Chapman, executive director of the Soy Foods Association, North America."That's responsible, to look at long-term effects, both positive andnegative."

Cooke defended the results of the study, but quelled media concern that hisstudy should be a warning. "I'm not out to be alarmist, or needlesslysuggest that there should be concern when maybe there's no reason to, but it'san area that need to be looked into," he said.