Author: Picherit C, Coxam V, Bennetau-Pelissero C, Kati-Coulibaly S, Davicco MJ, Lebecque P and Barlet JP
Publication: J Nutr. 2000 Jul;130(7):1675-81
Bone loss occurs when there is more bone resorption than bone formation. An important cause of bone loss with women is the low level of estrogen after menopause. Hormone replacement therapy is often recommended to these women but this therapy has some negative side effects, such as the increased risk of breast cancer. Natural therapies, including the consumption of isoflavones and food rich in isoflavones, are becoming more popular. The consumption of soybeans which are very rich in isoflavones has been link with many health benefits, including lower risk of arthrosclerosis, some cancers, bone loss and easing of typical menopausal symptoms (vaginal dryness and hot flushes). Although isoflavones are 1000 to 10.000 times less biological active than human estrogen (17 beta estradiol) their plasma concentration can rich high concentration, up to 1000 times as high as estrogen. Depending on the type of estrogen receptor, isoflavones can act as weak estrogens or as anti-estrogens. Other studies have shown that isoflavones might improve bone mass of humans.
The purpose of this study was to investigate the ability of isoflavones genistein and daidzein to prevent bone loss in ovariectomized rats. Ovariectomized rats do produce almost no estrogen and they obtain similar serum isoflavones levels than humans, making them ideal models for postmenopausal women. The tests were carried out on 65 female rats. They were divided in different groups depending on the type of isoflavones or estrogen that was fed:
- Control group of rats which were not ovariectomized
- Ovariectomized rats
- Genistein group of ovariectomized rats (daily 10 mcg genistein per gram body weight)
- Daidzein group of ovariectomized rats (daily 10 mcg daidzein per gram body weight)
- Ovariectomized rats treated with 17 alpha-ethinylestradiol (daily 30 mcg pr kg body weight).
After 3 months, the bone mineral density was determined in the lumbar vertebrae, femur and its metaphyseal and diaphyseal zones. As expected, the ovariectomized rats showed lower bone mineral density than the not ovariectomized rats. Rats treated with daidzein and 17 alpha-ethinylestradiol, but not with genistein, kept their initial bone mineral density. Image analysis performed in the distal femur metaphysis revealed that the cancellous bone area was lower ovariectomized rats than in the control group. In addition, the bone turnover was higher in the ovariectomized rats but not in those treated with daidzein. The intake of genistein or daidzein did not influence the uterine weight of the ovariectomized rats.
The study concluded that 17 alpha-ethinylestradiol and daidzein were more efficient than genistein in preventing both cancellous and cortical bone loss in rats in ovariectomized rats. Neither genistein nor daidzein exerted an estrogenic affect on the uterus demonstrating the safety of isoflavones for the treatment of postmenopausal bone loss.