Objective: To perform a systematic review and meta-analysis of all randomized, controlled trials of isoflavone supplementation to determine the efficacy of isoflavone therapy in reducing the number of daily menopausal flushes.
Methods: A comprehensive search of published studies of isoflavone treatment and menopausal flushing was undertaken. Studies were selected if they were randomized, were placebo controlled, provided the number of baseline flushes, the variance in flushes and the reduction in flushes. Effects for isoflavone treatment compared to control were calculated and a meta-analysis was performed. Regression analysis, weighted for the size of the study was performed to investigate the relationship between the dose of isoflavone, or number of baseline flushes and the reduction in flushes achieved compared to control.
Results: Isoflavone supplementation was found to be associated with a significant reduction in flushes (effect size -0.28, 95% confidence intervals -0.39 to -0.18, P < 0.0001). Marked heterogeneity was found between the studies, but the effect remained significant when analyzed using a random effects model (delta = -0.49, 95% confidence intervals -0.81 to -0.17, P = 0.001). The percentage reduction in flushes was significantly related to the number of baseline flushes per day and the dose of isoflavone studied (beta = -0.49 and -0.26, respectively, both P < 0.0001).
Conclusions: These results suggest that isoflavone supplementation may produce a slight to modest reduction the number of daily flushes in menopausal women and that the benefit may be more apparent in women experiencing a high number of flushes per day.