A new study in mice reported that preconception use of the phytoestrogen genistein could adversely affect and pregnancy outcomes, depending on the dosage and duration of exposure. The study was published in the journal Reproductive Toxicology.

Long-term exposure to genistein before conception affected pregnancy rates in mice, which caused prolonged labor, smaller litters and pups, and higher rates of pup mortality.

Genistein is an isoflavone found in soy foods and dietary supplements. Women consume it to get relief from menopausal conditions such as hot flashes, weight gain, and depression. Information about its potential effects on reproduction in adult women is very less.

The previous study reported that treatment with another phytoestrogen found in liquorice inhibited the ability of isolated ovarian follicles to grow and made sex steroid hormones.

In the present study, adult female mice consumed a diet containing 300, 500 or 1,000 ppm of genistein to examine chronic genistein exposure effects on sex steroid hormone levels and pregnancy outcomes. While, their control group consumed soy- and phytoestrogen-free diet. The mice were exposed to genistein for 1, 2, 5 or 8 months.

The gestation time was decreased after one month of exposure and mice had fewer pups in their litters after two months of exposure. In the mice that consumed 500 ppm/1000 ppm of genistein, pregnancy rate decreased after five months of exposure. In both groups, 83% of the females were fertile.

After five months of treatment, only 50% of mice that consumed 300 ppm of genistein were fertile while 67% of those in the control group were fertile. However, genistein increased fertility rates in the two highest dose groups (83% in the 500-ppm group and 100%in the 1,000-ppm group conceived).

The potential impacts of long-term phytoestrogen use were not fully known. Women should be careful about phytoestrogen exposure, especially when they plan to conceive in the future, the research team said.

Illinois alumna Shreya Patel, the investigator of the study, said that people should be aware of their consumption and certain supplements might not be safe. Hence, they should consult a doctor or a dietitian.

Pre-clinical studies revealed that chronic preconception exposure to phytoestrogen genistein adversely affects female fertility.