Record ID: MS-N098
Family: Foods and dietary supplements
Clinical question: Does long-term aged-garlic extract plus garlic oil prevent gastric cancer in a high-risk population?
Evidence label: Large randomized factorial trial; incidence negative, mortality signal uncertain
Evidence at a glance
Benefit: No significant reduction in gastric-cancer incidence; mortality was lower at 22.3 years with a borderline confidence interval.
Certainty: Moderate for the specific regimen and population, but generalizability and the delayed mortality finding are uncertain.
Risk: Garlic supplements can cause gastrointestinal effects and may increase bleeding risk or interact with anticoagulants.
Cancer control: The regimen is not established as a substitute for Helicobacter pylori testing, eradication, endoscopic surveillance or treatment.
What was studied
The Shandong Intervention Trial enrolled 3,365 adults aged 35–64 in a high-risk region of Linqu County, China. In a masked factorial design, 1,678 received aged garlic extract 400 mg twice daily plus steam-distilled garlic oil 2 mg twice daily and 1,687 received placebo for 7.3 years. Follow-up continued for 22.3 years.
Other randomized factors included two-week H. pylori treatment among seropositive participants and vitamin C, vitamin E and selenium. Factorial analysis separates these interventions but the population and baseline risk remain specific.
What the results mean
Through 2017, 151 gastric cancers and 94 gastric-cancer deaths were identified. Garlic did not significantly reduce incidence: 66 of 1,606 versus 81 of 1,631 in the fully adjusted analysis (OR 0.81, 95% CI 0.57–1.13).
Gastric-cancer mortality was 36 versus 54 deaths (HR 0.66, 95% CI 0.43–1.00). The upper confidence bound and delayed emergence make this a cautious signal, not proof that garlic supplements prevent death. H. pylori treatment produced a clearer reduction in incidence.
Limits and uncertainty
The result applies to a specific aged extract/oil regimen used in a rural Chinese population with unusually high gastric-cancer risk. It does not establish benefit for raw garlic, culinary intake or other supplements.
The mortality finding was based on 90 deaths in the fully adjusted comparison and was not accompanied by a significant incidence reduction. Later subgroup analyses are exploratory.
Safety and practical context
Garlic supplements may cause odor, reflux or gastrointestinal upset and can increase bleeding tendency, especially around surgery or with anticoagulant/antiplatelet medicines.
Evidence-based prevention includes H. pylori testing and treatment when indicated, tobacco avoidance, risk-based endoscopic surveillance and management of precancerous lesions.
Questions for the care team
- Am I in a high-risk population comparable to this trial?
- Have I been tested and treated for H. pylori when appropriate?
- Could anticoagulants, antiplatelet drugs or upcoming surgery make garlic unsafe?
- Is the claim about incidence, mortality or an exploratory subgroup?
Sources
- 22.3-year Shandong trial follow-up (PMID 31511230)
- Full-text trial report
- ClinicalTrials.gov record NCT00339768
- NIH ODS supplement safety context for garlic
Funding and conflicts
The long-running trial involved Chinese public-health and academic institutions with international collaborators. Detailed grant support and disclosures are available in the full report; no commercial garlic product should claim equivalence without matching the tested regimen.
Last literature search: October 21, 2026
Record appraised: October 21, 2026
This educational record is not individualized medical advice. Research doses and schedules are not personal prescriptions; do not delay or replace evidence-based cancer care.
