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Pure Appl. Chem., Vol. 70, No. 9, pp. 1777-1783, 1998

    Natural and anthropogenic environmental oestrogens:
    the scientific basis for risk assessment

    Dietary phyto-oestrogens and cancer

    S. Bingham
    MRC Dunn Clinical Nutrition Centre, Hills Road, Cambridge CB2 2DH, UK.

    Introduction: The significance of the structural similarity of the lignans and isoflavones to mammalian oestrogens and possible effects on cancer prevention were first promulgated in the early 1980s in publications of Setchell and of Adlercreutz (ref. 1). Since that time the literature on the possible health benefits of the isoflavones found predominantly in soy beans, has expanded exponentially, mainly in response to funding initiatives by the US government and soy bean industries, and more lately by European and UK Ministries of Food. Despite their more widespread occurrence in foods, and greater consumption in western populations, the lignans have received comparatively little attention.

    In vitro studies have established that plant oestrogens are oestrogenic, since they have the ability to bind to mammalian oestrogen receptors. Their affinity to receptors (from rabbit, sheep and rat uterine receptors, and a human cancer cell line) has been compared with oestradiol. Coumestrol has the greatest affinity, only 10 -20 times lower than oestradiol; and genistein about 100 times less. Daidzein and equol bind about 1000 times less. Similar findings are evident when their ability to increase uterine weight of mice is studied (ref. 2).

    However, although these weak oestrogens bind to the oestrogen receptor complex, they fail to stimulate a full oestrogenic response of replenishment of oestrogen receptors and protein synthesis. They have thus been characterised as antagonising oestradiol and acting as both oestrogens and antioestrogens, at least in rats. Newer studies have shown that they bind especially to b oestrogen receptors (ref. 1- 3). Since they are eaten in comparatively high amounts, they are therefore able to interfere with the feedback system of the release of gonadotrophins and thus account for fertility problems in animals (ref. 4). Enterolactone has also been shown to have antioestrogenic effects, suppressing rat uterine RNA synthesis induced by oestradiol (ref. 5).

    The cancers most closely linked to plant oestrogens are the hormone related sites of breast and prostate, and bowel cancer, which are less common in soy consuming populations. Cross sectional studies demonstrated higher levels in urine and plasma samples from individuals in these populations and also in vegetarians (refs. 6-9). However, as yet there have been few detailed epidemiological studies relating intakes of plant oestrogens to individual risk of these diseases. For the time being evidence that increased intakes would be beneficial is derived from experimental and physiological findings.

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