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Soy, red clover, and isoflavones and breast cancer: a systematic review.

  • 2013-11-28
  • PloS one 8(11)
    • Heidi Fritz
    • Dugald Seely
    • Gillian Flower
    • Becky Skidmore
    • Rochelle Fernandes
    • Sarah Vadeboncoeur
    • Deborah Kennedy
    • Kieran Cooley
    • Raimond Wong
    • Stephen Sagar
    • Elham Sabri
    • Dean Fergusson

Study Design

Type
Systematic Review
Sample size
n = 131
Population
women with breast cancer and women at risk of breast cancer
Methods
We searched MEDLINE, Embase, the Cochrane Library, and AMED from inception to March 2013 for human interventional or observational data pertaining to the safety and efficacy of soy and red clover isoflavones

Background

Soy and red clover isoflavones are controversial due to purported estrogenic activity and possible effects on breast cancer. We conducted a systematic review of soy and red clover for efficacy in improving menopausal symptoms in women with breast cancer, and for potential impact on risk of breast cancer incidence or recurrence.

Methods

We searched MEDLINE, Embase, the Cochrane Library, and AMED from inception to March 2013 for human interventional or observational data pertaining to the safety and efficacy of soy and red clover isoflavones in patients with or at risk of breast cancer.

Results

Of 4179 records, we included a total of 131 articles: 40 RCTs, 11 uncontrolled trials, and 80 observational studies. Five RCTs reported on the efficacy of soy for hot flashes, showing no significant reductions in hot flashes compared to placebo. There is lack of evidence showing harm from use of soy with respect to risk of breast cancer or recurrence, based on long term observational data. Soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50mg isoflavones) may be protective against breast cancer and recurrence. Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues. Prospective data of soy use in women taking tamoxifen does not indicate increased risk of recurrence. Evidence on red clover is limited, however existing studies suggest that it may not possess breast cancer-promoting effects.

Conclusion

Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (≥ 100 mg) isoflavones can be recommended for breast cancer patients.

Research Insights

  • Soy→Increased Circulating Estradiol Level

    Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues.

    Effect
    Neutral
    Effect size
    Small
    Dose
    not stated
  • Soy→Reduced Breast Cancer Incidence

    Soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50mg isoflavones) may be protective against breast cancer and recurrence.

    Effect
    Beneficial
    Effect size
    Large
    Dose
    25-50 mg isoflavones (2-3 servings daily)
  • Soy→Reduced Breast Cancer Mortality

    Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality.

    Effect
    Beneficial
    Effect size
    Large
    Dose
    25-50 mg isoflavones (2-3 servings daily)
  • Soy→Reduced Breast Cancer Recurrence

    Soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50mg isoflavones) may be protective against breast cancer and recurrence.

    Effect
    Beneficial
    Effect size
    Large
    Dose
    25-50 mg isoflavones (2-3 servings daily)
  • Soy→Reduced Hot Flashes

    Five RCTs reported on the efficacy of soy for hot flashes, showing no significant reductions in hot flashes compared to placebo.

    Effect
    Neutral
    Effect size
    Small
    Dose
    25-50 mg isoflavones (2-3 servings daily)

Adverse Events Reported

  • Soy→Overall tolerability

    Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues.

    Finding
    No significant difference
  • Soy→hot flashes

    Five RCTs reported on the efficacy of soy for hot flashes, showing no significant reductions in hot flashes compared to placebo.

    Finding
    No significant difference
  • Soy→Overall tolerability

    There is lack of evidence showing harm from use of soy with respect to risk of breast cancer or recurrence, based on long term observational data.

    Finding
    Reported
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