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Sulforaphane for Cancer Prevention

Verdict: Promising mechanism, no proven cancer prevention

For cancer prevention, sulforaphane (from broccoli sprouts) earns a Weak (Tier C) rating: human trials show only changes in detoxification and tumor-marker biomarkers, with no evidence that it actually lowers cancer incidence or mortality.

C 🟠 C Weak Evidence Published

🔬Why this grade7-layer evidence engine

The grade is held to weak because every human study stops at the biomarker level, not real cancer outcomes. A mechanistic review (PMID 29242678) confirms KEAP1-NRF2 as a validated chemoprevention target and sulforaphane as a strong inducer of phase II detoxification enzymes, but this is preclinical and cannot be extrapolated to human protection.

The two Qidong trials measured carcinogen handling, not cancer. The aflatoxin trial (PMID 16284385, n=200) found no overall difference between arms, only a correlation between the sulforaphane metabolite and lower carcinogen-DNA adducts; the air-pollutant crossover (PMID 22045030, n=50) raised excretion of carcinogen-glutathione conjugates by 20-50%. Both are surrogate signals only.

The single cancer-population RCT (PMID 25968598, n=78, prostate biochemical recurrence) missed its primary endpoint (PSA slope); only a secondary PSA doubling-time difference favored sulforaphane, which is a surrogate, not proof of fewer recurrences or longer survival. Regulators concur: the FDA notes these are unapproved supplements not evaluated for preventing any disease, and EFSA has left such botanical claims on hold. Cancer-prevention authorities advise against relying on supplements, so the honest verdict is that it does not yet work for preventing cancer.

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Scoring transparency

All scores computed by a 7-layer evidence engine — fully auditable
Raw score 0.45
D
C
B
A
S
← counter-evidence / ineffectiveeffective / strong evidence →
Final grade
C · Published
Confidence
61%
Broadly consistent
Evidence level
E6
Multiple smaller RCTs (n<500)

How strongly each layer supports this effect

lower = less supportive
L2 PubMedPrimary literature
0.40
L5 Clinical bodiesAuthoritative stance
0.40
L1 ExamineGlobal benchmark
0.50
L3 MechanismPlausibility
0.50
L11 AI re-checkIndependent read
0.50
Against Mixed Supports
▸View the full decision path (audit trail)
  1. compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.445
  2. tier_from_score — 依分數區間映射至 tier letter
  3. apply_hec_rules — 無高階證據可裁決
  4. tier_strict_requirement_check — Tier 條件達標，未降階
  5. detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
  6. decide_status — 依 tier + dispute 結果決定 status

📄PubMed studies (4)L2 · primary research & systematic reviews

Effect of Sulforaphane in Men with Biochemical Recurrence after Radical Prostatectomy
PMID: 25968598 2015 RCT (double-blind, placebo-controlled, multicenter) n = 78
Finding: Primary endpoint NOT met. Secondary outcomes favored sulforaphane: smaller mean PSA increase (+0.099 vs +0.620 ng/mL) and 86% longer PSA doubling time (28.9 vs 15.5 months) vs placebo; surrogate biomarker signal only, no hard cancer outcome (no effect on recurrence, metastasis, or survival demonstrated).
Effect size: PSA doubling time 28.9 vs 15.5 months (secondary, primary endpoint missed)
View on PubMed
Effects of glucosinolate-rich broccoli sprouts on urinary levels of aflatoxin-DNA adducts and phenanthrene tetraols in a randomized clinical trial in He Zuo township, Qidong, People's Republic of China
PMID: 16284385 2005 RCT (placebo-controlled) n = 200
Finding: No overall difference between intervention arms in aflatoxin-DNA adduct excretion; however, an inverse association was found between urinary dithiocarbamate (sulforaphane metabolite) levels and both aflatoxin-DNA adducts and phenanthrene tetraols, suggesting bioavailability-dependent carcinogen detoxification. Biomarker-level finding only; no cancer-incidence endpoint.
Government Effect size: Inverse association of dithiocarbamate excretion with carcinogen-DNA adducts (subgroup/correlation, not arm-level RCT effect)
View on PubMed
Modulation of the metabolism of airborne pollutants by glucoraphanin-rich and sulforaphane-rich broccoli sprout beverages in Qidong, China
PMID: 22045030 2012 RCT (crossover) n = 50
Finding: Statistically significant 20-50% increases in urinary excretion of glutathione-derived conjugates of benzene, acrolein and crotonaldehyde, indicating enhanced phase II detoxification of inhaled carcinogens. Biomarker (carcinogen clearance) endpoint only; no cancer-incidence outcome.
Government Effect size: 20-50% increase in pollutant-glutathione conjugate excretion
View on PubMed
KEAP1 and Done? Targeting the NRF2 Pathway with Sulforaphane
PMID: 29242678 2017 Narrative Review (mechanistic)
Finding: Summarizes KEAP1-NRF2 as a validated chemoprevention target and sulforaphane as a well-characterized NRF2 inducer that upregulates phase II detoxification/antioxidant enzymes; emphasizes preclinical anticarcinogenic activity. Mechanistic/preclinical anchor - does NOT establish human cancer-prevention efficacy on hard endpoints.
Academic Effect size: N/A (mechanistic review)
View on PubMed

🏛️Regulatory & authoritative positionsL4/L5 · FDA / EMA / NIH ODS / Cochrane / Mayo …

L4a US FDA
Cautious
Sulforaphane is not an approved drug and broccoli sprout / glucoraphanin products are marketed as dietary supplements; FDA has not evaluated them for the diagnosis, treatment, cure, or prevention of any disease. source↗
L4b EU EFSA
Neutral
1,548 claims on 'botanicals' have been placed on hold by the Commission pending further consideration on how to proceed with these source↗
L4d TW TFDA / 衛福部
Cautious
食品不得標示或廣告宣稱醫療效能 source↗
L5b Mayo Clinic
Cautious
L5c Cleveland Clinic
Cautious
L5d Harvard Health
Cautious
L5e Specialty Society (condition-mapped)
Cautious
✓PMID 100% verifiedevery citation checked via NCBI Entrez
🔬4 PubMed studiesindependently re-checked by multiple sub-agents
engine_version: v1.0 claim_id: CLM-COND-cancer-prevention-INT-sulforaphane-001 繁體中文版 →