Phytoestrogens are a diverse group of plant-derived compounds that structurally or functionally mimic mammalian estrogens (female sex hormones). There are three major classes of phytoestrogens.
The two major chemical classes of phytoestrogens found in the human diet are isoflavones and lignans. Phytoestrogens are found mostly in citrus fruit, cherries, berries, apples, grapes, celery, capsicum, broccoli, onions, tomatoes, red wine, flaxseeds, grains, nuts, chocolate, green tea, soya bean, legumes, clover, alfalfa, and spinach. Diadzein and genistein are the two best known isoflavones, and are found in soy-based food and beverages.
Phytoestrogens have long been associated with a reduction in risk of osteoporosis, heart disease and menopausal symptoms. Menopause is connected with decreased estrogen as the ovaries reduce their function significantly. The administration of phytoestrogens may help to reduce symptom related with menopause as an exogenous (outer) source of estrogen.
Polycystic ovary syndrome (PCOS) is a heterogeneous condition associated with menstrual irregularities and hyperandrogenic (elevetade concentrations of male sex hormones) state. Latest finding show that phytoestrogens administration in such case may help to improve function of reproductive system and increase the ovulation and pregnancy rates. However, more recently, phytoestrogens have been considered endocrine disruptors having the potential to cause adverse health effects.
Endocrine disruptors (ED)
Endocrine disruptors are chemical substances affecting endocrine system of human body. The effect of such chemical is dose-specific. This means, that in specific concentration does not manifest or present with beneficial effect while in different concentrations may prove detrimental for the health. The behaviour of endocrine disruptors also often varies in presence of other specific chemical substances which may significantly change its effect on endocrine systems. Quite much attention has been put to ED, as they often involve substances commonly used across all types of industry.
The role of phytoestrogens as endocrine disruptors is based upon their chemical properties. Thanks to structural similarities of phytoestrogens to human estrogens, they can bind to specific sites known as estrogen receptors (cell communication “node”). The unique structural configuration enables phytoestrogens to display estradiol-like effects; estradiol is the prevalent estrogen. Phytoestrogens also modulate the concentration of endogenous estrogens (estrogens produced by the body) by binding or inactivating some enzymes and also affect the bioavailability of sex hormones by depressing or stimulating the synthesis of sex hormone binding globulin (SHBG).
Therefore, besides the known beneficial effects, these herbal hormones may have possible unfavourable effects in humans by interfering with the function of normal cellular activities, such as DNA replication (formation of new DNA) and cell cycle regulation leading to cancerous growth.
Special attention should be given to phytoestrogen consumption by kids/adolescents. When given at high doses (50 mg/kg), genistein causes delayed mammary gland morphogenesis (development). Further, genistein at 0.5 mg/kg causes increased ovulation, and at 50 mg/kg decreases ovulation. A precocious thelarche (postnatal breast development) occurring very early in a girl due to excessive intake of phytoestrogens in the form of soy was also reported.
There is a lack of information about long-term effect of phytoestrogens on human health and the complications which may arise from increased intake are yet not clarified. Due to the functional and structural differences of phytoestrogens, their biological activities are also highly variable. Usually abnormal estrogen levels are related to high dosage of soy protein. Increased estrogen in both genders manifests by alteration of hypotalamo-pituitary gonadal axis which is the hormonal cascade controlling the function of reproductive system. This may manifest by many complications related to reproductive health.
Increased intake of phytoestrogens may induce hyperestrogenic state of the body. It is known that hyperestrogenism may cause significant medical problems in both males and females. In particular, hyperestrogenism has been related to gynecomastia (increased breast development in males), hypogonadism (decreased function of gonads), reduced fertility in men, macromastia (excessively large breast in females), enlarged uterus and menstrual irregularities in women. In addition, hyperestrogenism represents a major risk factor for the rare male breast cancer.
There is a lack of information on the effect of phytoestrogens on the humans. Although there are many studies focusing on the benefits of phytoestrogens as therapeutic supplements replacing synthetic hormones, there are few studies focusing on long-term effects of these endocrine disruptors. The contemporary fashion is to focus on use of natural products. Yet is should be noted that “natural” does not necessarily mean harmless and safe. Further investigation of the biological mechanism at the base of observed hormonal alterations induced by phytoestrogens is needed. It should be advised against the use of nutritional supplements for superficial purpose.