Efficacy of isoflavones related to frequency of hot flushes

Soyfoods and soybean isoflavone supplements seem to be most effective at alleviating the hot flushes experienced during menopause when initially most frequent, report researchers in this quarter's Journal of Medicinal Food​.

Drs Mark Messina and Claude Hughes review the evidence to date on the impact of soyfoods and soy isoflavones on hot flush symptoms in women. The authors find a statistically significant relationship between initial hot flush frequency and treatment efficacy.

"Initial hot flush frequency explained about 46 per cent of the treatment effects, and hot flush frequency decreased by about 5 per cent (above placebo or control effects) for every additional initial hot flush per day in women whose initial hot flush frequency was five or more per day,"​ reported the team.

Soy has received attention as an alternative to conventional hormone replacement therapy (HRT) largely because it is a unique dietary source of isoflavones. However there have been conflicting results from trials measuring the ability of isoflavones to reduce menopausal symptoms, despite some evidence linking the dietary component to the lack of hot flushes experienced by Japanese women.

A Finnish study​ published in this month's Obstetrics and Gynecology​ journal found that supplements containing a soy compound were no better than a placebo at relieving the symptoms of menopause. However this study enlisted breast cancer survivors as subjects. The review by Messina and Hughes eliminated trials on breast cancer patients. They also eliminated non-blinded trials.

Out of 11 studies on soyfoods, only one found that women showed a significant decrease in hot flush frequency. The researchers note however that "the large placebo effect makes most of these trials underpowered to detect modest effects"​. In four out of six studies on isoflavone supplements, there was a positive link to reduced menopausal symptoms, the researchers report. But the baseline level of hot flush frequency was higher on average among participants in the supplement trials.

This led the scientists to the theory that efficacy increased with hot flush frequency, so that those women having around 10 hot flushes each day saw this frequency halved, while those experiencing only seven daily only saw a reduction of around three flushes, after taking isoflavones.

The researchers write that although conclusions based on the analysis should be considered tentative, "the available data justify the recommendation that patients with frequent hot flushes consider trying soyfoods or isoflavone supplements for the alleviation of their symptoms"​.

They add that future trials involving soyfoods and isoflavone supplements are warranted, "but should focus on women who have frequent hot flushes".​ The correlation between initial hot flush frequency and the extent of reduction of symptoms should also be studied, they said.

"Finally it would be interesting to determine whether isoflavones are more effective at preventing the onset of hot flushes when consumed before menopause (rather than alleviating them once they have already begun), "​ concluded the team.