A Cochrane review [Abstract] 1 included 43 trials involving a total of4 364 women comparing phytoestrogens with control. Very few trials had data suitable for combining in meta-analysis. There was no significant difference between Promensil (a red clover extract) and placebo either in the frequency of hot flushes (mean difference (MD) -0.93, 95% CI -1.95 to 0.10; I²=31%, 5 trials) neither in percentage reduction in hot flushes (MD 20.15, 95% CI -12.08 to 52.38, I²=82%, 2 trials). Some of the other trials found phytoestrogens alleviate hot flushes and night sweats but many of the trials were of low quality and underpowered. There was a strong placebo effect in most trials with a reduction in frequency ranging from 1% to 59% with placebo. There was also no evidence that the treatments caused oestrogenic stimulation of the endometrium when used for up to two years.
A meta-analysis 2 included 62 studies with 6653 women. Use of phytoestrogens was associated with a decrease in the number of daily hot flashes (pooled mean difference of changes, -1.31, 95% CI -2.02 to -0.61) and vaginal dryness score (pooled mean difference of changes, -0.31, 95% CI -0.52 to -0.10) between the treatment groups but not in the number of night sweats (pooled mean difference of changes, -2.14, 95% CI -5.57 to 1.29). Individual phytoestrogen interventions such as dietary and supplemental soy isoflavones were associated with improvement in daily hot flashes (pooled mean difference of changes, -0.79, 95% CI -1.35 to -0.23) and vaginal dryness score (pooled mean difference of changes, -0.26, 95% CI -0.48 to -0.04). Several herbal remedies, but not Chinese medicinal herbs, were associated with an overall decrease in the frequency of vasomotor symptoms. 74% of the included randomized clinical trials demonstrated a high risk of bias within 3 or more areas of study quality.
Comment: The quality of evidence is downgraded by study quality (very variable quality), by inconsistency (variability in results across studies and heterogeneity in interventions and outcomes), and by indirectness (differences in studied patients).
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