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Soy Causes Infertility

Kaayla T. Daniel, PhD

Author of The Whole Soy Story: the Dark Side of America's Favorite Health Food


January 11, 2006


Santa Fe, NM:   Research published in this month's Biology of Reproduction shows that genistein, a plant estrogen found in soybeans, can disrupt the development of the ovariesof newborn female mice, causing reproductive problems and infertility.

“This is a wakeup call for parents and pediatricians,” says Kaayla T. Daniel, PhD, author of The Whole Soy Story: The Dark Side of America's Favorite Health Food. “Soy infant formula contains high levels of phytoestrogens that can adversely affect the development of a baby's ovaries and other reproductive organs. This study adds to a growing body of evidence linking soy genistein and other phytoestrogens to endocrine disruption. Clearly soy consumption must be considered a factor in America's epidemic of infertility.”

The study, conducted by researchers at the National Institute of Environmental Health Sciences (NIEHS), involved giving injections of soy genistein to three different groups of female mice during the first five days of their lives. The researchers found adverse effects at all levels, including at doses comparable to the amount of genistein found in soy infant formulas given to human infants. Mice treated with the highest dose were infertile and mice treated with the lower doses were subfertile, meaning they had fewer pregnancies and fewer pups per litter. Mice receiving the highest level of genistein showed a high percentage of oocyte (egg cell) clustering, making fertilization much less likely to occur.

“We knew that genistein was linked to reproductive problems later in life but we wanted to find out when the damage occurred,” says Retha R. Newbold, a developmental endocrinologist at NIEHS. “The study showed that genistein caused alterations to the ovaries during early development, which is partly responsible for the reproductive problems found in adult mice.” A previous NIEHS study showed that newborn mice given genistein grew up to experience irregular menstrual cycles, erratic ovulation and other problems indicative of infertility.

“I don't think we can dismiss the possibility that these phytoestrogens are having an effect on the human population,” said Wendy Jefferson , PhD, lead author of the study. NIEHS director Dr. David Schwartz commented, “Although we are not entirely certain about how these animal studies on genistein translate to the human population, there is some reason to be cautious.”

“The NIEHS is not alone in recommending caution,” says Dr. Daniel. “Last July the Israeli Health Ministry warned that babies should not receive soy formula and that children up to age 18 should eat soy foods or drink soy milk no more than once per day to a maximum of three times per week. The ministry was most concerned about adverse effects on fertility. The French government has also taken these dangers seriously, and is now implementing regulations that will require manufacturers to remove most of the soy estrogens from soy formula and from soy foods targeted to children under 3.“

Although the strongest warnings against soy formula come from Israel and France, the

United Kingdom's Chief Medical Officer and the British Dietetic Association have warned pediatricians and parents to use soy formula only a last resort. In New Zealand, the Health Ministry has suggested that doctors carefully monitor the thyroids of infants on soy infant formula. “Sadly, here in the United States the myth that soy is a 'health food' has led to increased use of soy formula, which now constitutes nearly 25 percent of the bottle-fed market,” says Dr. Daniel.

“The evidence is mounting that soy formula puts infants at risk for reproductive problems, including infertility,” says Dr. Daniel. “I hope this important new study will encourage the United States to follow the examples set by the Israeli and French governments and issue warnings that will discourage the sale of soy formula. A good policy is 'Better safe than sorry.'”

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