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Side Effects of Phytoestrogens: A Meta-analysis of Randomized Trials
American Journal of Medicine, 09/29/09

Tempfer CB et al. – Based on the available evidence, phytoestrogen supplements have a safe side–effect profile with moderately elevated rates of gastrointestinal side effects. Rates of vaginal bleeding, endometrial hyperplasia, endometrial cancer, and breast cancer were not significantly increased among phytoestrogen users in the investigated studies.

Methods

• Using a fixed–effects model, the authors performed a meta–analysis of side effects comparing phytoestrogen treatment with placebo or no treatment in randomized controlled trials.

Results

• The authors identified 174 randomized controlled trials. Side effects were reported in 92/174 randomized controlled trials with 9629 participants.
• The overall incidence of side effects in the phytoestrogen and control groups was 2019/5502 (36.7%) and 1824/4806 (38.0%), respectively.
• Comparing various side effect categories, we found significantly higher rates of gastrointestinal side effects among phytoestrogen users.
• Gynecological, musculoskeletal, neurological, and unspecific side effects were not significantly different between groups.
• Specifically, the rates of hormone–related side effects such as endometrial hyperplasia, endometrial cancer, and breast cancer were not significantly different between groups.