Phyto-oestrogens through the life cycle
Cassidy, A. and Faughnan, M. 2000. Proceedings of the Nutrition Society. 59:489-496.
Substantial epidemiological and experimental evidence supports the protective role of phytoestrogens in human health. The physiological behavior during absorption and metabolism and the clinical relevance of such effects is limited. Similar to other weakly estrogenic compounds, phytoestrogens have the potential to exert antagonistic effects, and may have actions comparable with selective estrogen receptor modulators (SERMS). These effects include exertion of estrogenic effects in vascular and bone tissues, and antiestrogenic effects on breast and reproductive tissue. Lignans and isoflavones are two major classes of phytoestrogens, obtained from flaxseed and soya bean respectively. After ingestion phytoestrogens are absorbed and metabolized by the action of intestinal microflora. Large intra- and inter-individual variability appears to exist in the metabolic fate of these compounds. Phytoestrogens are able to cross the placenta and some animal evidence suggests that in utero exposure may provide beneficial effects, such as reducing the risk of developing breast cancer in later life. Evidence suggests that phytoestrogens ingestion appears to lower the incidence of many hormone-dependent diseases, including coronary heart disease (CHD), menopausal symptoms, osteoporosis and breast cancer, and that beneficial effects occur in both premenopausal and postmenopausal women. Limited data exists on the optimal intake of phytoestrogens to provide potential health benefits. Different intakes may be required to provide various effects and some data from human trials suggest that the intake required to exert effects on bone may exceed that required to alter lipoprotein metabolism and antioxidant activity. Because of their potential to act as SERMS, phytoestrogens are being investigated as a potential natural alternative to conventional hormone replacement therapy. Clinical evidence suggests phytoestrogens may have several beneficial effects in women, including the ability to decrease menopausal symptoms and prevent bone loss, and decrease CHD through various effects such as lowering lipid levels (cholesterol), and decreasing platelet activation and aggregation. In relation to men’s health, there is speculation that phytoestrogens may play a role in reducing the risk of prostatic cancer. Further clinical research is needed in these areas to confirm the potential beneficial effects. As well, the physiological behavior of phytoestrogens, the doses required to exert biological and specific health effects, and the influence of factors such as age and sex is limited, and thus, further research is needed.