Effects of phyto-oestrogens on tissues

Recent investigations on the effects of phyto-oestrogens on various tissues have revealed that these diverse molecules may improve human health, parti cularly by protecting against certain chronic diseases. After a brief exami nation of the food sources, structures, and general cellular actions of the major phyto-oestrogens, current research findings on cardiovascular diseas e, skeletal tissues, and reproductive cancers are reviewed. Phytooestrogen concentrations in blood may be maintained at high levels in those consuming soyabean (Glycine max)-based food daily at several meals and exert their e ffects on target cells through either genomic effects via the classical oes trogen receptors or non-genomic effects mediated by membrane-bound oestroge n receptors or other cellular proteins. The expression of oestrogen recepto r (OR) subtypes alpha (alpha) and beta (beta) varies across tissues, and ce lls that preferentially express OR-beta which may include bone cells, are m ore likely to respond to phyto-oestrogens. Conversely, reproductive tissues contain relatively more OR-alpha and may, thus, be differently affected by phyto-oestrogens. Soyabean phytooestrogens appear to prevent the progressi on of atherosclerosis through multiple interactions, including lowering of plasma lipids and lipoproteins, increased vasodilatation and, possibly, dec reased activation of blood platelets and vascular smooth muscle cells. Howe ver, a favourable impact on cardiovascular disease morbidity and mortality by a soyabean-enriched western-type diet remains to be shown, and unresolve d questions remain regarding dose and form of the phyto-oestrogens in relat ion to risks and benefits. The isoflavones of soyabean have been shown cons istently to have bone-retentive effects in animal studies by several invest igators using rodent models, although intakes must be above a relatively hi gh threshold level for a lengthy period of time, and little or no extra ben efit is observed with intakes above this threshold level. The reports of mo dest or no effects on prevention of bone loss in human and non-human primat e studies respectively, may be due to the limited doses tested so far. The relationship between soyabean-food intake and cancer risk has been more ext ensively investigated than for any other disease, but with less certainty a bout the benefits of long-term consumption of phyto-oestrogen-containing fo ods on prevention of cancer. The observations that breast and prostate canc er rates are lower in Asian countries, where soyabean foods are consumed at high levels, and the high isoflavone content of soyabeans have led to exam ination of the potential protective effects of phytooestrogens. Establishin g diet-cancer relationships has proved difficult, in part because of the co nflicting data from various studies of effects of soyabean-diets on cancer. Epidemiological evidence, though not impressive, does suggest that soyabea n intake reduces breast cancer risk. The isoflavone genistein has a potent effect on breast cancer cells in vitro, and early exposure of animals to ge nistein has been effective in reducing later development of mammary cancer. Thus, continuous consumption of soyabean foods in early hfe and adulthood may help explain the low breast cancer mortality rates in Asian countries. Although the evidence for a protective effect against prostate cancer may b e slightly more supportive, more research is needed before any firm conclus ions can be made about the phyto-oestrogen-cancer linkages.