DOES IT WORK?Phytoestrogens and menopausal symptoms
LAST WEEK’S column examined new evidence that the side effects of phytoestrogens appear to be limited to gastrointestinal problems. Earlier animal studies had suggested that these products could have serious side effects, but this has not been borne out by the research conducted to date. These results do not address whether phytoestrogens are effective in relieving menopausal symptoms.
Phytoestrogens are a large group of compounds found in many different plant foods. These include wheat, barley, sunflower seeds, many nuts, gooseberries, yams and some vegetables. The best known sources of phytoestrogens used for the relief of menopausal symptoms are soy and red clover.
This connection began with epidemiological studies which are large surveys of people’s lifestyle factors and their health. Such studies reported significant differences in the menopausal symptoms of women in Asia compared with European and American women.
For example, about 25 per cent of Asian women report hot flushes after menopause compared with 80 per cent of European women and 85 per cent of American women.
The researchers then noticed a connection between these trends and soy consumption. Women in Asian countries generally consume much higher quantities of soy and soy products.
Epidemiological studies are designed to suggest possible links between various factors and health.
Once such connections are proposed, they must be tested in controlled trials to show whether the factors actually cause those health changes. Over the past several years, many controlled trials have been conducted to examine whether or not soy and other phytoestrogen-containing supplements bring relief of menopausal symptoms.
The results of randomised controlled trials of phytoestrogens for menopausal symptoms have not been consistent. The majority have found that the supplements are no better than placebo, although some have found beneficial effects.
Even in these beneficial studies, the effects were modest and tended to disappear after about six weeks. When the results of these studies are combined in systematic reviews, the overall effects are not beneficial.
One of the explanations for the inconsistencies has been the variety of supplements tested. Soy and red clover are the most common, with very few red clover studies finding beneficial effects. In studies using soy, a higher proportion report relief of menopausal symptoms.
Further examination of these studies suggests that soy may be more beneficial for certain women, and not helpful for all.
For example, beneficial effects are more commonly found when the studies enrolled women with mild to moderate symptoms compared with those with more severe symptoms.
Also, when menopause is triggered suddenly, such as can happen with certain diseases, after a hysterectomy or with some cancer treatments, soy did not relieve menopausal symptoms.
Relief was more commonly found when menopause developed slowly and naturally.
Phytoestrogens also appear to be more beneficial when they have been part of a woman’s diet for many years prior to menopause compared with when women start the supplements when menopausal symptoms develop.
Phytoestrogens are found naturally in many foods and are safe when taken in dietary quantities. Some people experience gastrointestinal side effects, most commonly constipation, bloating or flatulence, nausea or vomiting, and abdominal pain.
More serious side effects arising from phytoestrogens’ hormone-related actions have not been found in controlled trials.
Phytoestrogens are a large group of compounds with different ones having different effects in different women. The use of red clover for menopausal symptoms is not supported by the available studies.
However, the evidence regarding soy and soy products is more variable. Soy contains compounds in addition to phytoestrogens and these may help menopausal symptoms also.
Soy appears to be most beneficial soon after menopause and when the symptoms are relatively mild. The greatest benefits appear to arise when soy has been included in a balanced, plant-rich diet for years prior to menopause.
The average Asian diet contains 25-40mg phytoestrogens per day, although women have taken up to 100mg per day without adverse effects.
Used alone, there is little evidence that phytoestrogens are effective in treating more severe menopausal symptoms.
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
