Фитоэстрогены: растительные ксеноэстрогены и их влияние на организм

Plant derived xenoestrogen
A phytoestrogen is a plant derived xenoestrogen (a type of estrogen produced by organisms other than humans) not generated within the endocrine system, but consumed by eating plants or manufactured foods. Also called a "dietary estrogen", it is a diverse group of naturally occurring nonsteroidal plant compounds that, because of its structural similarity to estradiol (17 β estradiol), have the ability to cause estrogenic or antiestrogenic effects. Phytoestrogens are not essential nutrients because their absence from the diet does not cause a disease, nor are they known to participate in any normal biological function. The similarities, at molecular level, of an estrogen and a phytoestrogen allow them to mildly mimic and sometimes act as an antagonist of estrogen. but it was unknown if they could have any effect in human or animal metabolism. In the 1940s and early 1950s, it was noticed that some pastures of subterranean clover and red clover (phytoestrogen rich plants) had adverse effects on the fecundity of grazing sheep.

Phytoestrogens mainly belong to a large group of substituted natural phenolic compounds: the coumestans, prenylflavonoids and isoflavones are three of the most active in estrogenic effects in this class. but also occurring elsewhere, e. g. on various forages. Although mycoestrogens are rarely taken into account in discussions about phytoestrogens, these are the compounds that initially generated the interest on the topic.

Phytoestrogens exert their effects primarily through binding to estrogen receptors (ER). There are two variants of the estrogen receptor, alpha (ER α) and beta (ER β) and many phytoestrogens display somewhat higher affinity for ER β compared to ER α. In vitro studies show an activation of PPARs at concentrations above 1 μM, which is higher than the activation level of ERs. At the concentration below 1 μM, activation of ERs may play a dominant role. At higher concentrations (>1 μM), both ERs and PPARs are activated. Studies have shown that both ERs and PPARs influence each other and therefore induce differential effects in a dose dependent way. The final biological effects of genistein are determined by the balance among these pleiotrophic actions. Soybeans naturally produce isoflavones, and are therefore a dietary source for isoflavones. Phytoestrogens are ancient naturally occurring substances, and as dietary phytochemicals they are considered to have coevolved with mammals. In the human diet, phytoestrogens are not the only source of exogenous estrogens. Xenoestrogens (novel, man made), are found as food additives and ingredients, and also in cosmetics, plastics, and insecticides. Environmentally, they have similar effects as phytoestrogens, making it difficult to clearly separate the action of these two kind of agents in studies.

The consumption of plants with unusual content of phytoestrogens, under drought conditions, has been shown to decrease fertility in quail. Parrot food as available in nature has shown only weak estrogenic activity. Studies have been conducted on screening methods for environmental estrogens present in manufactured supplementary food, with the purpose of aiding reproduction of endangered species.

In humans, phytoestrogens are digested in the small intestine, poorly absorbed into the circulatory system, circulate in plasma, and are excreted in the urine. Metabolic influence is different from that of grazing animals due to the differences between ruminant versus monogastric digestive systems.

It is unclear if phytoestrogens have any effect on the cause or prevention of cancer in women. Some epidemiological studies have suggested a protective effect against breast cancer. Additionally, other epidemiological studies found that consumption of soy estrogens is safe for patients with breast cancer, and that it may decrease mortality and recurrence rates. It remains unclear if phytoestrogens can minimize some of the deleterious effects of low estrogen levels (hypoestrogenism) resulting from oophorectomy, menopause, or other causes.

It is unclear if phytoestrogens have any effect on male sexuality, with conflicting results about the potential effects of isoflavones originating from soy. Sperm count decline and increasing rate of testicular cancers in the West may be linked to a higher presence of isoflavone phytoestrogens in the diet while in utero, but such a link has not been definitively proven. Furthermore, while there is some evidence that phytoestrogens may affect male fertility, more recent reviews of available studies found no link, and instead suggests that healthier diets such as the Mediterranean diet might have a positive effect on male fertility.

Some studies have found that some concentrations of isoflavones may have effects on intestinal cells. At low doses, genistein acted as a weak estrogen and stimulated cell growth; at high doses, it inhibited proliferation and altered cell cycle dynamics. This biphasic response correlates with how genistein is thought to exert its effects. Some reviews express the opinion that more research is needed to answer the question of what effect phytoestrogens may have on infants, but their authors did not find any adverse effects. Studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy based infant formula compared to conventional cow milk formula. The American Academy of Pediatrics states: "although isolated soy protein based formulas may be used to provide nutrition for normal growth and development, there are few indications for their use in place of cow milk based formula. These indications include (a) for infants with galactosemia and hereditary lactase deficiency (rare) and (b) in situations in which a vegetarian diet is preferred."

In some countries, phytoestrogenic plants have been used for centuries in the treatment of menstrual and menopausal problems, as well as for fertility problems. Plants used that have been shown to contain phytoestrogens include Pueraria mirifica and its close relative kudzu, Angelica, fennel, (black cohosh is also used for menopausal symptoms, but does not contain phytoestrogens).