Evidence suggesting that soya-based infant formulas could damage infants' abilities to fight off disease has been published this week. Research from the US suggests that some chemicals contained in soya can suppress the immune system, at least in mice.
Soya-based infant formulas are widely used by parents who cannot breast feed or use formulas based on cow milk. Scientists have suggested that parents who are able to use an alternative to soya formulas should consider doing so, although they stressed that their research had been based on an animal models and as such did not prove any risk to humans.
The research was carried out by a team led by Dr Paul S. Cooke at the University of Illinois in Urbana. When researchers injected mice with the plant oestrogen genistein, which is found in soy products, they discovered that the levels of several immune cells dropped. Furthermore, the size of the thymus, a gland where immune cells mature, was significantly smaller after taking the oestrogen.
The researchers also tested whether the same effects were seen after eating genistein, since soya products are usually consumed rather than injected. They found that the thymus shrank after the mice ate a diet containing genistein, a worrying development since the levels of genistein found in their blood was lower than would normally be found in human babies after eating infant formula.
Despite the findings, Cooke stressed that parents should not stop using soya-based formulas at all costs, since the research had focused on mice, not humans. Furthermore, soya-based formulas have been used for decades, and the researchers suggested that if there were any significant adverse effects from soya, they would have become clear already.
Cooke said his team would continue to look at the effects of genistein in a bid to discover exactly how it affects the immune system. He added that until similar trials were carried out on human subjects, however, the research would be incomplete.
The findings were published in the Proceedings of the National Academy of Sciences (2002; 99:7616-7621).