Penn Researchers Take A Long-Term Look At The Safety
Of Soy-Based Infant Formula
PA) To understand whether hormone-like chemicals in
soy products may influence sexual development in children,
researchers at the University of Pennsylvania School
of Medicine have revisited a study on soy-based infant
formula begun over thirty years ago.
Their results, published in this week's Journal of the
American Medical Association, reaffirm the safety of
soy infant formula and offer evidence against the harmful
effects of soy that have been presented in the popular
media. According to their findings, soy formula does
not appear to lead to any more health or reproductive
problems than cow milk formula.
"We have found that, in terms of sexual development,
there is very little difference between children who,
as infants, were fed cow milk formula and those fed
soy formula," said Brian L. Strom, MD, MPH, director
of the Penn Department of Biostatistics and Epidemiology.
"The biggest concern has been whether or not phytoestrogens
in soy had a 'feminizing' effect on children."
Strom is quick to add, however, that the idea is not
entirely unfounded. Phytoestrogens, which occur naturally
in soy, are analogous to the human female hormone estrogen.
Infants fed soy formula receive relatively high doses
of phytoestrogen during a time of life when they are
rapidly growing. It comes as no surprise, then, that
the possibility of altering a child's development had
concerned some parents and scientists.
"In this study, we interviewed young adults who
had been part of feeding studies as infants," said
Strom. "We were looking for abnormalities in their
adolescent and sexual development attributable to their
early exposure to soy phytoestrogens."
This study has its roots in a landmark study at the
University of Iowa, which first started looking at the
effects of soy formula on infants beginning in 1965
and lasting until 1978. At the time, soy was still relatively
new to the American diet. Then, as now, soy was seen
as an excellent source of nutrition for infants, especially
for infants who are allergic to - or cannot properly
digest - cow's milk.
Strom and his colleagues took up the task of tracking
down and interviewing 811 adults - some from almost
30 years after the Iowa study began - and comparing
those that had been fed soy formula with those that
had been fed milk formula.
The researchers asked the participants a long list of
questions regarding the timing and events in their puberty
and sexual development that might have been effected
by phytoestrogens. For the women, they had an array
of questions regarding menstruation, physical development,
and fertility. For the men, they inquired about possible
delayed sexual maturity and fertility problems. They
also asked the participants about other possible effects,
such as, hormonal disorders, cancers, sexual orientation,
Despite the large number of comparisons made, the groups
were essentially indistinguishable. Menstrual bleeding
in the soy-fed group was, on average, about one third
of a day longer, although without heavier bleeding.
Soy-group participants also seemed to experience slightly
more discomfort with menstruation, but they were not
more likely to seek medical attention for pain or cramps.
"The differences were borderline and - given the
number of questions we asked and the size of the study
- were probably due to chance," said Strom. "The
differences do, however, make leads for follow-up studies."
Strom believes that it would be interesting to revisit
these 'formula infants' as they reach their middle and
elder years, and says that work still needs done to
understand the effects of long-term exposure to phytoestrogens.
While breast feeding remains the preferred means of
sustenance for infants, soy formula has been shown to
be an excellent source of nutrition for infants. Nearly
20% of all infants in the United States are fed soy
formula sometime during their first year of life.
"The good news is that, for children that need
formula, soy formula is as safe as cow milk-based formula,"
said Strom. "As always, the public should be skeptical
of accounts that are based on speculation and case reports,
rather than proper science."
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