Soy Linked to Abnormal Egg Development

Abnormal clustering of egg cells
in mice treated with genistein
© Syracuse University

Genistein, a phytoestrogen, is the primary naturally occurring oestrogen in plants, which can mimic the effects of oestrogen in the body. Previous research showed that female mice given genistein immediately after birth had irregular menstrual cycles, problems with ovulation, and problems with fertility in their adulthood. Researchers of Syracuse University undertook this study to determine when this damage occurs.

Newborn female mice were given different doses of genistein during their first five days of life. The genistein was comparable to what human infants might receive in a soy-based formula (6-9 mg/kg per day). All of the mice that were treated were affected by genistein in some way. The mice that received low levels of genistein were subfertile, meaning they had fewer pups in each litter and fewer pregnancies. The mice that received the high dose were infertile, and the mice with the highest dose were infertile and had a high percentage of eggs that remained in clusters and did not develop normally. In order for an egg to be able to be fertilised, it must break down from clusters into individual eggs (oocytes). The researchers believe that genistein inhibits this process.

The largest difference between the treated and untreated mice occurred at six days of age, when untreated mice had 57 percent single or unclustered egg cells, compared to only 36 percent found in genistein-treated mice.

“It is not yet clear how genistein works and how it causes these effects,” says Melissa Pepling, assistant professor of biology at Syracuse. Although human testing has not yet been conducted, Pepling points out that pregnant or nursing mothers should be cautious when considering using soy-based products. Experiments on pregnant mice do not show effects of genistein on the ovary, but do show other developmental abnormalities.; Source: Syracuse University