A new study has found that genistein, a component of soy, can disrupt the development of the ovaries in newborn female mice. The researchers, from the National Institute of Environmental Health Sciences (NIEHS), say the new findings add to a growing body of literature demonstrating the potentially adverse consequences of genistein on the reproductive system. While the results were observed in mice, the researchers believe that caution is warranted. "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," said Dr. David A. Schwartz, Director of NIEHS. "More clinical studies are needed to determine how exposure during critical windows of development can impact human health."
Genistein, a naturally occurring estrogen, can be found in foods containing soy such as soy-based infant formulas, as well as over-the-counter dietary supplements. Previous research had showed that mice given genistein immediately after birth had irregular menstrual cycles, problems with ovulation, and problems with fertility as they reached adulthood. The new study, published in the journal Biology of Reproduction, looked at the direct effects of genistein on the ovaries during early development.
"We knew genistein was linked to reproductive problems later in life, but we wanted to find out when the damage occurs," said Retha R. Newbold, author on the study. "The [new] study showed that genistein caused alterations to the ovaries during early development, which is partly responsible for the reproductive problems found in adult mice."
"We think genistein inhibits the oocytes, or egg cells, from separating apart," said researcher Wendy Jefferson. "Since there are many egg cells in the same follicle instead of just one, the resources from the surrounding cells are spread too thin and they can't get the support they need to become a mature functioning egg cell."
"I don't think we can dismiss the possibility that these phytoestrogens [such as genistein] are having an effect on the human population," added Dr. Jefferson. "They may not show their effects or be detected until later in life, but chances are they are having an effect."
Source: National Institute of Environmental Health Sciences
