DOES IT WORK?Phytoestrogens are relatively safe for women, especially for those under 55
PHYTOESTROGENS ARE a diverse group of compounds found in many plants and food supplements. They have become widely used by women to treat menopausal symptoms.
Menopause is triggered when a woman’s body starts producing lower levels of female hormones, particularly oestrogen.
For some women, the transition is relatively smooth, but others experience hot flushes, depression, vaginal dryness and irritation, and other symptoms.
Their severity also can vary significantly. Hormone replacement therapy is effective in relieving many of these symptoms, but concerns have been raised about its possible side effects. For this reason, many have looked to natural remedies, including phytoestrogens.
Phytoestrogens come in many forms and include flavonoids such as genistein and daidzein, found in soy and red clover; coumestans such as coumestrol, found in soybeans; and lignans, found in flaxseed.
Studies found that in cultures where phytoestrogen intake is high (especially through soy and soy-based foods), the incidence of menopausal symptoms is lower. However, concerns have been expressed about the potential side effects of phytoestrogens, especially when taken for long periods of time.
Little evidence has been available in this area, but in the October issue of the American Journal of Medicine, Austrian researchers published a report systematically summarising all the available evidence in this area.
They concluded that apart from increased risks of gastrointestinal problems, phytoestrogens are as safe as placebo or no treatment when taken for menopausal symptoms.
Evidence from studies
Concerns initially arose from laboratory studies that showed that phytoestrogens work by mimicking the action of oestrogen. While this can compensate for the lower production of oestrogen at menopause, it could cause problems.
Studies with various cells showed that phytoestrogens can stimulate the growth of certain cancer cells and they can counteract the effects of some anti-cancer drugs. However, other laboratory studies showed that phytoestrogens have protective effects against some cancers.
The Austrian researchers sought to provide clear guidance by examining studies involving women taking phytoestrogens. They collected information from randomised controlled trials of phytoestrogens which documented any side effect.
They found 92 such trials, involving almost 10,000 women. They summarised the data using a statistical method called meta-analysis. The result allowed them to compare the incidence of various side effects in women taking phyto- estrogens with the incidence in those taking a placebo or having no treatment.
The overall incidence rate was 37 per cent in the phytoestrogen groups compared with 38 per cent in the control groups. That difference is not statistically significant.
The researchers then looked at particular side effects. Of special interest was the finding that the rates of hormone-related side effects, such as endometrial cancer, breast cancer and endometrial hyperplasia, and of vaginal bleeding, were not significantly different between the groups.
The only significant difference was that higher rates of gastrointestinal side effects were found in women taking phytoestrogens compared with those in control groups.
The Austrian researchers also examined whether the duration of treatment affected the rate of side effects. Unexpectedly, they found that women using phytoestrogens for longer periods reported fewer side effects.
However, they also found that women over 55 years were more likely to experience side effects than women under 55.
Recommendations
This study provides important reassurance for women taking phytoestrogens. There is a moderately increased risk of gastrointestinal side effects, most commonly constipation, bloating or flatulence, nausea or vomiting, and abdominal pain. However, the incidence of more serious side effects was not higher than in women taking a placebo or no treatment. This is an especially welcome finding.
At the same time, some caution is warranted when interpreting these data. The methods used to combine many studies involving different phytoestrogens could hide a serious side effect from one particular compound.
Also, the average length of these studies was relatively short (six months), and uncommon, but serious, side effects from long-term treatment might have been missed. Nonetheless, this report provides important evidence that phytoestrogens are relatively safe for women, particularly women under 55 years.
Importantly, however, this study did not examine whether or not phytoestrogens are effective in relieving menopausal symptoms. That question will be addressed in next week’s column.
- Dónal O'Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University
