Influence of phytoestrogens on endometrial thickness: a systematic review and meta-analysis

The objective of this systematic review was to evaluate the influence of the use of phytoestrogens on variations in endometrial thickness in postmenopausal women. Randomized controlled trials were searched in the following electronic databases until March 2020: MEDLINE, Embase, Cochrane Library, Web of Science and LILACS. We used the terms 'phytoestrogens' and 'endometrium' or 'endometrial hyperplasia' to search for relevant trials. The data were analyzed using RevMan 5.3 software. A total of 10 studies involving 1476 patients were included. The difference in endometrial thickness was evaluated in 10 studies, with a total of 805 participants in the phytoestrogen group and 761 in the control group. Such a difference was not significant between groups after 3 months (standardized mean difference [SMD] 0.00, 95% confidence interval [CI] - 0.37 to 0.37; I² = 63%), 6 months (SMD -0.30, 95% CI -0.79 to 0.19; I² = 70%), 12 months (SMD -0.02, 95% CI 0.22 to -0.18; I² = 0%) and 24 months (SMD -0.09, 95% CI -0.25, 0.08; I² = 0%) of use. Our meta-analysis shows no changes in endometrial thickness in women using phytoestrogens. Evidence is still uncertain owing to the presence of heterogeneity among the studies currently available, whose reported outcomes cover a period between 3 and 6 months.