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The effects of phyto-oestrogens on menopause symptoms and other conditions

Alyson Huntley discusses how soy and other plants may prevent hot flushes and reduce bone loss

Alyson Huntley discusses how soy and other plants may prevent hot flushes and reduce bone loss

Epidemiological data from Asian countries suggests that a diet rich in phyto-oestrogens may be the basis of a less problematic menopause and play a preventive role in other diseases. Phyto-oestrogens bind to the oestrogen receptors but only weakly (about 1,000 times weaker than 17-ß oestradiol) and can act as both agonists and antagonists.

The most widely studied phyto-oestrogen compounds are the isoflavones daidzein and genistein, found abundantly in the soya bean (Glycine max) and also in a supplement made from red clover (Trifolium pratense L).

Menopausal symptoms

There are many randomised controlled trials of phyto-oestrogens investigating a variety of formats and dosages, and mainly looking at the effect on hot flushes. One recent systematic review concluded that the evidence for the effectiveness of soya preparations is mixed and that the frequency of hot flushes was not reduced with red clover extracts1. However, a further more comprehensive systematic review that divided high-quality trials into the different phyto-oestrogen sources concluded that although overall the evidence was unconvincing, the results from six out of seven randomised controlled trials of soya bean isoflavone extracts suggested a reduction in hot flushes of around 50% of the improvement expected with conventional HRT2. Figures from these trials show no effect of phyto-oestrogen supplementation on vaginal symptoms.

Bone density

There is a large amount of animal data suggesting retention of bone mass with phyto-oestrogen supplementation. The human studies are flawed by being short term (six to 12 months) and lacking appropriate outcome measures, although they are, as with the animal studies, suggestive of a beneficial effect of isoflavones on bone health.

Of particular interest are studies using isolated isoflavone extracts. One double-blind randomised controlled trial compared pure genistein with HRT and a placebo group. Some 90 women aged 47 to 57 were randomised to one of the three groups for 12 months. At six and 12 months, both genistein and HRT significantly reduced excretion of pyridinium cross links (marker of bone retention) and increased bone mass density of the femur and lumbar spine, with no effect seen in the placebo group3.

Cardiovascular risk factors

There are studies that describe the effect of phyto-oestrogens on lipid markers, blood pressure and endothelial function. Meta-analysis of trial data has suggested that soya food or protein (but not isolated isoflavones) has some beneficial effect on lipid markers4. The data on blood pressure and endothelial function are mixed. The evidence that phyto-oestrogens have any effects on blood pressure is sparse but the positive studies are with soya bean protein. Effects seen with soya bean protein and endothelial function include increased flow mediated dilatation and improved peripheral vascular resistance but the results are not consistent. Positive results have also been reported for isolated isoflavones and endothelial function.

There are suggestive indications from epidemiological data in Asian countries, but there is no definitive evidence to suggest a protective effect of phyto-oestrogens against breast cancer. Equally, though, there is no indication that prolonged use of an isoflavone-rich diet induces malignant growth of hormone-dependent tissue.

A 12-month controlled trial of 177 women (aged 49 to 65 years), randomised either to red clover isoflavones (42mg standardised product) or placebo showed that neither group exhibited any changes in breast density5. Endometrial tissue status is routinely monitored in most trials of phyto-oestrogens in the menopause and no adverse effects have been seen in the short term (six months or less).

However, in one five-year study in which 376 postmenopausal women were randomised to 150mg of soy isoflavones or placebo, five cases of simple hyperplasia and one complex hyperplasia were seen in the active group compared with no cases in the placebo group6. Although there are fewer cases of colorectal cancer in Asian countries compared with Western countries, soya bean or isoflavone intake cannot be positively associated with the lower rate.

Cognitive function and diabetes

There are insufficient data on phyto-oestrogen intake and cognitive function to draw a meaningful conclusion. The studies on diabetes in postmenopausal women are mixed in terms of their study population, different phyto-oestrogen preparations and outcome measures. They suggest a positive effect for diabetes control and this effect is thought to be due to the soluble fibre content as opposed to a specific effect of isoflavones.

Dosage

Studies involve a wide variety of phyto-oestrogen preparations and dosages, but the menopause studies use in the region of 60-120mg of isolated isoflavones daily. The bone health literature quotes 100mg of isolated isoflavones daily as being an efficacious dose. It is important to note that the bioavailability of these potentially active phyto-oestrogens are affected by many factors including which format they are in (food stuff, pure isoflavones) frequency of ingestion, individual metabolism and other dietary factors.

Alyson Huntley is a freelance researcher for NICE's National Collaborating Centre of Women's and Children's Health and a past research fellow in complementary medicine at the Universities of Exeter and Plymouth

Competing interests: None declared

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