Beneficial And Adverse Effects Of Phytoestrogens In Humans

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4.5.1 Introduction

The bulk of the available data on the effects of phytoestrogen on humans is mostly from postmenopausal women, and in particular on the effects on hot flushes. Data are beginning to emerge on the effect of phytoestrogens in bone, but very little is known about the effects of these compounds on the uterus and breast. This information is urgently required to allow evaluation of long-term safety of these compounds, particularly in view of long-term treatment of postmenopausal women for the prevention of osteoporosis. Very little is known about the therapeutic potential of phytoestrogen in men.

4.5.2 Effects of Soy or Red Clover Derived Phytoestrogen on Climacteric Symptoms

To date, six randomized studies (Murkies et al., 1995; Albertazzi et al., 1998; Washburn et al., 1999; St Germain et al., 2001; Kotsopoulos et al., 2000; Knight et al., 2001) have investigated the effect of soy or other pulses on incidence and severity of hot flushes in perimenopausal and postmenopausal women (Table 4.1). Some of the studies utilized soy as whole grains, some in flour form. Other studies have utilized isolated soy protein that is a soy-derived powder containing over 90% protein and a high concentration of isoflavones. This is possibly a more physiological diet-like way of administering isoflavones as it maintains intact the original food matrix, which may be of importance for absorption and clinical efficacy.

The results of studies on the effects of soy on hot flushes are quite contradictory. Three studies have failed to observe any effects (St Germain et al., 2001; Kotsopoulos et al., 2000; Knight et al., 2001), while others have observed some benefit. Soy preparations appear, at best, to only halve the incidence of hot flushes (Albertazzi et al., 1998), which is somewhat in contrast with a complete lack of hot flushes observed in Japanese women (Lock, 1993).

One could argue that efficacy may be improved by extracting and concentrating in tablets the compound considered to be the active principal of soy. This should also, at least theoretically, improve compliance. Western women, in general, do not find the traditional Japanese diet easy to follow, hence, isolated isoflavones in tablet form have been used.

Four studies (Scambia et al., 2000; Upmalis et al., 2000; Han et al., 2002; Faure et al., 2002) using isolated isoflavones in tablet form have been performed to date (Table 4.2). Doses ranging from 50 to 100 mg per day were used. Again, at best, number of hot flushes was halved. This is not an obvious improvement in the treatment effects over those achieved with whole soy and suggests that the effect of these compounds is small. It will be necessary to use a large population size with a high number of severe symptoms to obtain an effect that is statistically significant.

Table 4.1

Randomized placebo-controlled studies performed with soy and other grains.

Table 4.1

Randomized placebo-controlled studies performed with soy and other grains.

Trial reference

Phytoestrogen source


Trial type and duration

Hot flushes

Murkies et al. (1995). Maturitas, 21, 189195.

45 g soy flour, 45 g wheat flour

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