Exposure to the phytoestrogen genistein prior to conception may adversely affect female fertility and pregnancy outcomes, depending on the dosage and duration of exposure, a study of the University of Illinois (UI) found.
UI researchers found that chronic preconception exposure to genistein affected pregnancy rates in mice and was associated with prolonged labor, smaller litters and pups, and higher rates of pup mortality.
For the study, the researchers fed adult female mice a diet containing 300, 500 or 1,000 parts per million of genistein, while their counterparts in the control group consumed food that was soy- and phytoestrogen-free. The groups of mice that consumed genistein were exposed to it for 30, 60, 150 or 240 days, which produced blood serum concentrations equivalent to those found in women who consume soy foods or supplements.
"When we looked at animals exposed for 30 days, the gestation time, the length of time they were pregnant, was decreased, similar to premature births," said Jodi Flaws, a professor of comparative biosciences at UI and a co-author of the study. "And after 60 days' exposure, they had fewer pups in their litters."
After 150 days, the mice that consumed 500 ppm or 1000 ppm of genistein were less likely to become pregnant after mating. Only 83 percent of the females in either of those groups were fertile, the researchers found.
After 240 treatment days, only 50 percent of mice in the 300-ppm group were fertile compared with 67 percent of those in the control group.
While mice in the 240-day treatment group that gave birth bore normalized litters, they often killed their pups, and the pups were much smaller than peers of similar age.
Although the findings are preliminary, the researchers said that little is known about the potential effects of long-term phytoestrogen use, and women should be cautious about their exposure, especially if they plan to conceive in the near future.
The findings add to a growing body of research that raises troubling questions about the potential health risks of long-term exposure to plant-based estrogens. Genistein is an isoflavone found in soy foods and dietary supplements, and, like other plant estrogens, may be consumed by women to relieve menopausal conditions such as hot flashes, weight gain and depression.
The study has been accepted for publication in the journal Reproductive Toxicology.
