A Review of the Evidence for the Use of Phytoestrogens as a Replacement for Traditional Estrogen Replacement Therapy

Abstract

Estrogen replacement therapy (ERT) is recommended for postmenopausal women primarily for reduction of menopausal symptoms and prevention of osteoporosis and cardiovascular disease. However, only 35% to 40% of women ever start ERT, and many do not continue it. One of the reasons women are reluctant to receive postmenopausal ERT is that they perceive prescription estrogens as being "unnatural." Because of this, there is increasing interest in the use of plant-derived estrogens, also known as phytoestrogens. This article reviews the evidence for the potential of phytoestrogens, either in dietary or supplemental form, to replace traditional forms of ERT. A comprehensive search of the English-language literature identified more than 1000 articles published in the past 30 years about phytoestrogens. In total, 74 studies were selected for inclusion in this review based on relevance, inclusion of human subjects wherever possible, and study design. The studies examine phytoestrogens' inhibition of the growth of cancer cell lines in vitro and in animals. They also look at the role of phytoestrogens in the reduction of cholesterol levels, and the use of one phytoestrogen derivative, ipriflavone, in the prevention of osteoporosis. Some small studies examine the role of phytoestrogens in the prevention of menopausal symptoms. Evidence for the potential health benefits of phytoestrogens is increasing. However, the clinically proven health benefits of prescribed ERT far outweigh those of phytoestrogens. Therefore, there is insufficient evidence to recommend the use of phytoestrogens in place of traditional ERT, or to make recommendations to women about specific phytoestrogen products.

Neurobehavioral effects of dietary soy phytoestrogens

“…They are abundant in fruits, vegetables, legumes, whole grains and especially flaxseed, clover and soy products, and they have many of the physicochemical and physiological properties of estrogens [1,2,4,10,17,18,42,56,61,62,83,86,94,101,102,104,110,117]. The three main classes of phytoestrogens of clinical interest are: (1) isoflavones (derived principally from soybeans and clover), (2) lignans (found in flaxseed in large quantities) and (3) coumestans (derived from sprouting plants like alfalfa) [1,2,4,10,17,42,56,61,62,83,86,94,101,102,104,117]. Of the isoflavones, genistein and daidzein are thought to exert the most potent estrogenic hormone activity and thus most of the research attention has been directed toward these molecules [2,4,17,42,56 -59,83,94,101,102,104].…”

“…Phytoestrogens have been shown in animal models and in limited clinical investigations to be protective in the prevention of: (1) hormone-dependent cancers (e.g., breast and prostate), (2) cardiovascular disease, (3) osteoporosis and (4) to alleviate the symptoms of menopause (such as hot flashes) [1,2,4,5,11,42,56,60,61,83,86,94,101,102,104,110,117,126]. The anticancer effects of phytoestrogens appear to be associated with several possible mechanisms including their ability to inhibit tyrosine kinase(s), growth factors, DNA topoisomerase, steroidogenic enzymes and to act as antioxidant and antiangiogenic agents [1,2,4,5,11,34,56,60,61,83,86,101,102,104].…”

“…In the examination of the use of soy, for example, consumption of tofu in Asian countries can be documented for thousands of years [11], whereas the introduction and growing of soybeans in the USA have taken place only within the last 100 years [11]. Moreover, the awareness of the potential health benefits and consumption of soy products [103] in the USA has only increased within recent years [1,2,4,5,11,42,101,102,104,117]. The relatively high consumption of soy in Japan corresponds to the relatively low incidence of PCa and BCa compared to that in the USA.…”

“…Conversely, the benefits of phytoestrogens compared to hormone replacement therapy (HRT) in women have received increased media attention directed mainly at the prevention and treatment of perimenopausal and menopausal symptoms [42,117]. While there is evidence to suggest that phytoestrogens may alleviate many of the symptoms of menopause [42,117], there are abundant data demonstrating the proven health benefits of traditional HRT compared to the relatively small number of clinical studies validating the effectiveness of phytoestrogens in treating menopausal symptoms.…”

“…While there is evidence to suggest that phytoestrogens may alleviate many of the symptoms of menopause [42,117], there are abundant data demonstrating the proven health benefits of traditional HRT compared to the relatively small number of clinical studies validating the effectiveness of phytoestrogens in treating menopausal symptoms. Effects on hot flushes are modest in comparison to that observed for HRT, but nevertheless, there is an indication from the relatively low rates of hot flushes in Japan that the lifelong exposure to soy isoflavones may be a more important determinant of the effectiveness in reducing symptoms of the menopause.…”