Effects of phytoestrogens on female estrogen sensitive tissues are discussed controversially. There is growing evidence that exposure early in life may have a larger (and lasting) impact than an exposure later in life.
To further investigate this issue we performed a study in female Wistar rats. Animals were divided into three groups: Group K received a phytoestrogen free diet, group P phytoestrogen rich diet and G a phytoestrogen free diet supplemented with genistein (Gen, daily intake 100 mg Gen/kg per BW) prior to mating, throughout pregnancy and up to weaning. Their offspring were kept on the diets during growth and then sacrificed at the age of 25, 50 or 80 days.
In groups G and P significant increases of the Gen plasma levels were detected. At day 25, the uterine wet weight, the height of the uterine epithelium and the expression of complement C3 were significantly stimulated in group G animals compared to the K and P group. At day 80 no significant differences were observed between the treatment groups and the control group. Interestingly, at day 50 the uterine wet weight was significantly increased in groups G and P. The trabecular bone mineral (BMD) density of the groups G, but also P was significantly elevated compared to group K, both in juvenile rats (at day 25) and in adult rats (at day 80).
In summary, our results demonstrate that exposure to phytoestrogens during gestation, lactation and growth increases the BMD of juvenile but also adult female rats. Interestingly, a phytoestrogen rich diet results in an increase of BMD but in contrast to the administration of GEN, does not stimulate estrogen sensitive uterine parameters. These findings support the hypothesis that lifelong exposure to phytoestrogen by diet may be responsible for the different epidemiology of fracture risks in eastern and western countries and may protect against osteoporosis.