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Phytonutrients and outcomes following breast cancer: a systematic review and meta-analysis of observational studies.

  • 2023-12-09
  • JNCI cancer spectrum 8(1)
    • M Diana van Die
    • Kerry M Bone
    • Kala Visvanathan
    • Cecile Kyrø
    • Dagfinn Aune
    • Carolyn Ee
    • Channing J Paller

Study Design

Type
Meta-Analysis
Population
breast cancer survivors
Methods
MEDLINE, EMBASE, CINAHL, Cochrane Library, ClinicalTrials.gov, and the ISRCTN registry were searched for prospective and retrospective observational studies; random-effects model used for meta-analysis

Background

Phytonutrient intakes may improve outcomes following breast cancer, but the impact of postdiagnosis introduction vs established prediagnostic exposure as well as optimum doses has not been established. Evidence from observational studies for key exposures was evaluated, including dosage and intake time frames.

Methods

MEDLINE, EMBASE, CINAHL, Cochrane Library, ClinicalTrials.gov, and the ISRCTN registry were searched for prospective and retrospective observational studies investigating the impact of soybean, lignans, cruciferous (cabbage-family) vegetables, green tea, or their phytonutrients on breast cancer survival outcomes. A random-effects model was used to calculate summary hazard ratios (HRs) and 95% confidence intervals (CIs). Nonlinear dose-response analyses were conducted using restricted cubic splines.

Results

Thirty-two articles were included. Soy isoflavones were associated with a 26% reduced risk of recurrence (HR = 0.74, 95% CI = 0.60 to 0.92), particularly among postmenopausal (HR = 0.72, 95% CI = 0.55 to 0.94) and estrogen receptor-positive survivors (HR = 0.82, 95% CI = 0.70 to 0.97), with the greatest risk reduction at 60 mg/day. In mortality outcomes, the reduction was mostly at 20 to 40 mg/day. Soy protein and products were inversely associated with cancer-specific mortality for estrogen receptor-positive disease (HR = 0.75, 95% CI = 0.60 to 0.92). An inverse association was observed for serum or plasma enterolactone, measured prediagnosis and early postdiagnosis, with cancer-specific mortality (HR = 0.72, 95% CI = 0.58 to 0.90) and all-cause mortality (HR = 0.69, 95% CI = 0.57 to 0.83). No effects were observed for cruciferous vegetables. There was a 44% reduced risk of recurrence with prediagnostic green tea for stage I and II breast cancer (HR = 0.56, 95% CI = 0.38 to 0.83).

Conclusions

Soy, enterolactone, and green tea demonstrated significant risk reductions in outcomes following breast cancer. Evidence is needed regarding the impact of postdiagnostic introduction or substantial increase of these exposures.

Research Insights

  • Soy→Reduced All-Cause Mortality

    In mortality outcomes, the reduction was mostly at 20 to 40 mg/day.

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    20 to 40 mg/day (mortality reduction)
  • Soy→Reduced Breast Cancer Recurrence

    particularly among postmenopausal (HR = 0.72, 95% CI = 0.55 to 0.94) and estrogen receptor-positive survivors (HR = 0.82, 95% CI = 0.70 to 0.97)

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    60 mg/day (greatest risk reduction for recurrence)
  • green tea→Reduced Breast Cancer Recurrence

    particularly among postmenopausal (HR = 0.72, 95% CI = 0.55 to 0.94) and estrogen receptor-positive survivors (HR = 0.82, 95% CI = 0.70 to 0.97)

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    60 mg/day (greatest risk reduction for recurrence)
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