USA: A recent meta-analysis of observational studies showed significant risk reduction in outcomes after breast cancer with the intake of green tea, enterolactone, and soy. The findings were published online in JNCI Cancer Spectrum.
Novel findings of the study were the significant risk reduction with soy isoflavones for recurrence in estrogen receptor–positive survivors and the significant associations between enterolactone (ENL) and all-cause mortality and breast cancer–specific mortality for women with node-negative disease. Findings for the overall cohorts were otherwise consistent with those of previous meta-analyses examining high vs low intake

Previous studies have suggested improvement in outcomes following breast cancer with phytonutrient intakes. Still, the impact of postdiagnosis introduction versus established prediagnostic exposure and optimum doses has not been established. To fill this knowledge gap, M Diana van Die, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA, and colleagues aimed to inform patients, clinicians, researchers, and policymakers of the evidence from observational studies for lignans, soybean, green tea, and cruciferous vegetables, as well as their phytonutrients on breast cancer–specific mortality, breast cancer recurrence, and all-cause mortality, with a focus on the most effective dosage and time frame for consuming these exposures by conducting a systematic review and meta-analysis.
For this purpose, the researchers searched the online databases for retrospective and prospective observational studies investigating the impact of lignans, soybean, cruciferous (cabbage-family) vegetables, green tea, or their phytonutrients on breast cancer survival outcomes. Summary hazard ratios (HRs) were calculated using a random-effects model. Nonlinear dose-response analyses were conducted using restricted cubic splines. A total of thirty-two articles were included.
The researchers reported the following findings:
Soy isoflavones were associated with a 26% reduced risk of recurrence (HR = 0.74), particularly among postmenopausal (HR = 0.72) and estrogen receptor–positive survivors (HR = 0.82), with the greatest risk reduction at 60 mg/day. I
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).
An inverse association was observed for serum or plasma enterolactone, measured prediagnosis and early postdiagnosis, with cancer-specific mortality (HR = 0.72) and all-cause mortality (HR = 0.69).
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).
"To further inform clinical practice, there is a need for evidence on the impact of dietary and supplemental intakes of phytonutrients introduced or substantially increased following diagnosis and treatment," the authors write.
Reference:
Van Die, M. D., Bone, K. M., Visvanathan, K., Kyrø, C., Aune, D., Ee, C., & Paller, C. J. (2024). Phytonutrients and outcomes following breast cancer: A systematic review and meta-analysis of observational studies. JNCI Cancer Spectrum, 8(1). https://doi.org/10.1093/jncics/pkad104