الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
 |  | from | 148 |  |  |
| | | from | 148 | | |
المستخلص
Phytoestrogens are plant derived substances that are structurally and functionally similar to estrogens.
They are structurally classified into four chemical classes of phytoestrogens, isoflavonoid, coumestans, prenyl flavonoids and lignans.Exposure to these phytoestrogens is mainly through diet which are widespread in food, including herbs (hops), grains (soybeans, wheat and rice), vegetables (carrots and potatoes), fruits (date, pomegranates, cherries and apples), and drinks (coffee).
The chemical structure of phytoestrogens is similar to estrogens. So, they exhibit estrogenic activity by acting on estrogen receptors, but this activity is generally less than that of human estrogens (estrogenic activity ranges from 1/500 to 1/1000 of the activity of human estrogens). Therefore, they have both weak estrogen and anti estrogen activity as they can bind to ER and exhibit estrognic activity by ER activation and antiestrogenic activity by competitive binding to ER and inhibiting E2. So, they are termed as natural Selective Estrogen Receptor Modulator (SERMs). This SERMs like action make them very useful in various indication which include prevention of hormone dependent cancer, osteoporosis, menopausal symptoms and cardiovascular disease. However, this beneficial effect depends on tissue type and number of receptors in it, estrogen concentration, type of phytoestroges, its dose and time of exposure to it.
These factors may shift phytoestrogens from beneficial to harmful side for instance.
Isoflavones present in soy act as antiestrogens in breast tissues, but they act as proestrogens in bone tissues, but this effect is further dependant on the amount of phytoestrogens (isoflavones) and time of exposure to it.
As high isoflavone concentration above 10 μm exerts antiproliferation of breast cancer due to its antiestrogenic effect especially if taken during prepupertal period. However, if taken at low concentration below 100 nm, it exerts marked hyperproliferation of breast cancer due to its estrogenic effect.
So, these natural compounds especially natural herbs can have both good and bad health affects because too much of them can alter hormone dependant tissue structure and function. So, exposure to phytoestrogens are not always beneficial, as inappropriate exposure may be detrimental leading to reproductive disorders, cancer development in certain tissues, infertility and genotoxicity especially in infants because they exposed through soy baby milk to excessive amount in crucial time of their development.