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Methods Determine Estrogenization Effects in Infants

By Robin Arnette
March 2008

Lead author Judy Bernbaum is a pediatrician and investigator in the NIEHS-funded Soy Estrogens and Development (SEAD) Project.
Lead author Judy Bernbaum is a pediatrician and investigator in the NIEHS-funded Soy Estrogens and Development (SEAD) Project. (Photo courtesy of Steve McCaw)
Rogan is lead researcher in the SEAD project, which evolved from a 2004 review,
Rogan is lead researcher in the SEAD project, which evolved from a 2004 review, "Isoflavones in Soy Infant Formula: A Review of Evidence for Endocrine and Other Activity in Infants," authored by Rogan and former NIEHS Postdoctoral Fellow Aimin Chen. (Photo courtesy of Steve McCaw)

Some studies suggest that adults who consume foods rich in soy protein receive several health benefits such as healthy bones and a decreased risk of breast or prostate cancer, although research investigating diets rich in soy are in progress. However, soy isoflavones are weak estrogens and their affect on newborns, especially in regard to breast and genital development, is less established. In a pilot study to develop methods for investigating estrogen's effects in infants, researchers used several examination methods on babies who were fed breast milk, cow milk or soy formula. The team determined that measurement of breast tissue and characterization of vaginal wall cells could be used to evaluate the effects of estrogen exposure.

The team was comprised of investigators from the NIEHS Epidemiology Branch, Children's Hospital of Philadelphia, Children's Hospital Medical Center in Cincinnati, Westat, Inc. and Social & Scientific Systems, Inc. The study, titled "Pilot Studies of Estrogen-Related Physical Findings in Infants," appears in the March issue of Environmental Health Perspectives. (

According to Walter Rogan, M.D., principal investigator in the Epidemiology Branch at the NIEHS and corresponding author of the paper, the research attempted to address the hypothesis that compounds found in food or pollutant chemicals may have hormonal consequences in humans, such as undescended testicles or early puberty. "This study was an attempt to develop simple, reproducible methods for assessing whether a child exhibited effects consistent with estrogen exposure using physical examination and simple lab tests," Rogan explained.

Seventy-two children, 37 boys and 35 girls, from birth to six months of age, were divided into three groups. Each group was fed breast milk, soy formula or cow milk formula. The researchers measured breast adipose tissue, breast buds and testicular volume. They also observed breast and genital development and collected vaginal wall cells and information on vaginal discharge.

The team was aware that physical effects in newborns could be a response to the mother's estrogen, so they "looked at characteristics that exhibited declines from younger to older children," said Judy Bernbaum, M.D., director of the Neonatal Follow Up Program at the Children's Hospital of Philadelphia and lead author of the study.

The investigators reported that most of the infants from all three groups retained palpable adipose breast tissue at six months, but they did not observe a postnatal increase in breast bud size in males or females. Testicular volume occurred within the range reported in other studies, but because of a possible peak in testosterone at two months, further research with more frequent exams was warranted.

In all three groups, the maximal amount of breast tissue occurred in newborns and decreased in older children, but external genitalia showed few differences by age. In newborn girls vaginal wall cells were responsive to maternal estrogen and lost that effect by one month. However, the team was unable to determine whether cells after this period responded to estrogen produced by the infant or the estrogen in the soy formula.

Although the team was encouraged that the measurement of breast tissue and vaginal wall cells was a dependable test of estrogen exposure, Rogan stressed that the study was too small to have reliable findings about differences in feeding methods. He said, "None of the differences we observed between feeding groups were statistically significant, which is what we expected from this small study."

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