Green Tea Extract for Cancer Prevention
There is no reliable evidence that green tea extract supplements prevent cancer, and the highest-quality reviews are null or inconsistent. Because cancer-prevention use means long-term high-dose dosing, the well-documented risk of liver injury makes this an unfavorable bet.
Why this grade7-layer evidence engine
This earns a counter-evidence grade because the strongest synthesis points the wrong way. The 2020 Cochrane review (PMID 32118296) pooled 142 studies and over 1.1 million people, yet found only limited, inconsistent evidence: overall cancer incidence RR was 0.83 but not statistically significant (95% CI 0.65-1.07), and mortality was flat at RR 0.99. Crucially, the largest dedicated randomized trial, the Minnesota Green Tea Trial (PMID 28904061; 932 women on 843 mg EGCG/day for a year), was null on its primary breast-cancer risk biomarker.
The apparent positives do not hold up. A 2025 meta-analysis (PMID 40832777) reported modest reductions (green tea RR 0.91, EGCG RR 0.72), but its authors flag high heterogeneity and explicitly call for higher-quality validation. Site-specific signals, such as the prostate RR 0.38 in a small RCT subset (PMID 28353571), come from low-power or bias-prone observational designs, and the high-quality randomized evidence simply does not confirm a protective effect.
Regulators reinforce the caution. The US FDA recognizes green tea catechins only as a food antioxidant (GRAS), not as a cancer preventive, and the WHO's IARC classifies tea as Group 3 (not classifiable for carcinogenicity), which is neither a benefit nor a warning. Meanwhile the UK COT and EFSA tie EGCG doses at or above 800 mg/day to raised liver enzymes, so taking concentrated capsules long-term to chase an unproven benefit carries real hepatotoxicity risk. Note that any positive talk about brewed green tea the drink does not transfer to the extract supplement.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.485
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 negative 主導 (2 negative > 0 positive)，下層 RCT 不能推翻
- apply_hec_override — HEC-1 高階證據 negative — 強制由 C 改為 D
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status