Can H. pylori raise your bowel cancer risk?

By Dr Wong Nan-Yaw, MBBS (NUS), FRCS (Edinburgh). Published 4 Nov 2026. 7 min read.

Possibly, but it is not proven. Large observational studies link H. pylori, a common stomach infection, with a modestly higher chance of colorectal cancer and adenomas, and some suggest treatment lowers that risk. These are associations, not proof of cause, and they do not change Singapore's screening age of 50. Dr Wong Nan-Yaw is a colorectal and general surgeon.

What is H. pylori?

Helicobacter pylori is a bacterium that lives in the stomach lining. It is a common chronic infection, present in up to 31% of Singaporeans according to the National University Health System, and most people who carry it never have symptoms. It is a major risk factor for stomach and duodenal ulcers and for stomach cancer.

A simplified picture of H. pylori, a bacterium that lives in the stomach lining.

H. pylori is classed as a class I carcinogen because of its causal link with stomach cancer (Shah and colleagues, Journal of Clinical Oncology, 2024). The NUHS notes that developing cancer from the infection is uncommon for any one person, but because so many people carry it, it is an important cause of stomach cancer worldwide.

When it causes symptoms, these are usually from gastritis or an ulcer: upper abdominal pain or burning, bloating, feeling full after a small amount of food, nausea, or, with a bleeding ulcer, black stools or vomiting blood (NHS).

What does the research show about H. pylori and bowel cancer?

Several large studies have found that people with H. pylori infection have a somewhat higher rate of colorectal cancer and adenomas than people without it. The studies are observational, so they show an association. They cannot prove that the infection causes bowel cancer, because other differences between infected and uninfected people may explain part of the link.

Study	Who was studied	Main finding
Shah and colleagues, J Clin Oncol 2024	812,736 US veterans tested for H. pylori; 25.2% tested positive	Testing positive was linked with an 18% higher rate of colorectal cancer (adjusted hazard ratio 1.18) and 12% higher colorectal cancer deaths (1.12)
Li and colleagues, eClinicalMedicine 2025	Meta-analysis of 55 studies with 48,945,236 participants	Infection was linked with higher odds of colorectal cancer (odds ratio 1.59), adenoma (1.47) and advanced adenoma (1.77)
Han and colleagues, Gut 2026	Two Chinese trial cohorts of 3,365 and 180,284 people	Untreated infection was linked with a higher colorectal cancer risk (hazard ratio 2.96 in the smaller cohort, 1.27 in the larger)

Reported ratios from three H. pylori studies

Shah and colleagues, J Clin Oncol 2024 (adjusted hazard ratio)
Colorectal cancer1.18
Colorectal cancer deaths1.12
Li and colleagues, eClinicalMedicine 2025 (odds ratio)
Colorectal cancer1.59
Adenoma1.47
Advanced adenoma1.77
Han and colleagues, Gut 2026 (hazard ratio)
Colorectal cancer, smaller cohort2.96
Colorectal cancer, larger cohort1.27

Each dot is a ratio comparing two groups in one study, using the figures in the table above. A ratio of 1 means no difference between the groups. A dot is not a person's chance of cancer. The studies use different measures, so compare dots within a study rather than across studies.

Figures are taken from the published abstracts and full texts, read 2 November 2026. These figures compare groups using different statistical measures. They do not mean an 18% chance of cancer and cannot, by themselves, tell you your own risk. The meta-analysis authors reported high variation between the studies they combined (I-squared 89% for colorectal cancer), which lowers confidence in the exact size of the link.

Does treating H. pylori lower bowel cancer risk?

It may, but the evidence is mixed. In the US veterans study, people whose infection was untreated had a 23% higher colorectal cancer rate and a 40% higher death rate than those treated. One Chinese trial cohort showed a lower risk after treatment, while a much larger one showed no overall benefit after 13.8 years.

The Gut authors describe their findings as post hoc observational analyses of established trial cohorts, so they are not direct trial evidence on bowel cancer. The eClinicalMedicine authors conclude that large randomised trials with long follow-up are still needed to show whether treatment changes colorectal cancer rates.

US veterans: treatment was linked with an absolute reduction in colorectal cancer of 0.23% to 0.35% over 15 years of follow-up
Meta-analysis: treatment was linked with fewer colorectal cancers or adenomas (odds ratio 0.44), but this rested on only 3 retrospective studies
Shandong Intervention Trial: treatment was linked with lower colorectal cancer risk over 29.4 years (hazard ratio 0.47)
Mass Intervention Trial in Linqu: no overall benefit at 13.8 years (hazard ratio 1.17), with possible benefit only in people at high genetic risk or with antibodies to particular H. pylori proteins

How might a stomach infection affect the bowel?

The possible mechanisms are hypotheses, mostly from laboratory and animal research. The JCO authors suggest that bacteria and their products shed from the stomach may reach the lower bowel, that H. pylori may trigger inflammation in the bowel lining, and that it may change the bowel's mix of microbes in ways that favour polyp growth.

One mouse study cited by the JCO authors found that H. pylori infection activated inflammatory pathways in the colon and sped up tumour growth in mice prone to polyps. Animal findings do not necessarily apply to people. The JCO authors also note that severe stomach damage from long-standing infection has been linked with colorectal adenomas, which may point to shared pathways, but this too is unproven.

How is H. pylori tested for and treated?

H. pylori can be found with a urea breath test, a stool test, or a gastroscopy with biopsy. A blood antibody test shows exposure but cannot tell a current infection from a past one. Treatment is a course of acid-reducing medicine with antibiotics for 7 to 14 days, followed by a repeat test to confirm the infection has cleared.

Breath and stool tests can find the infection, and treatment is a course of medicines.

NUHS describes treatment as a proton pump inhibitor, which reduces stomach acid, with two antibiotics for 7 to 14 days, and states that confirming eradication afterwards is mandatory. The 2024 American College of Gastroenterology guideline prefers 14-day regimens and addresses the need for a test of cure after treatment in everyone treated. Take every dose as prescribed, because incomplete treatment can lead to the infection returning or to antibiotic resistance (NUHS).

Urea breath test: you swallow a drink or tablet and breathe into a tube; the bacteria break the test substance down and the products appear in your breath (NUHS, NHS)
Stool test: a sample of stool is checked for the bacteria (NHS)
Gastroscopy: allows the stomach to be examined for ulcers and samples to be taken (NUHS)
Blood antibody test: shows past exposure, so a positive result does not confirm active infection (JCO 2024)

Does H. pylori change bowel cancer screening in Singapore?

No. Singapore's national programme invites people aged 50 and above to screen for colorectal cancer every year with a stool test (FIT), or by colonoscopy every 10 years (Ministry of Health). H. pylori infection does not change that starting age. People with bowel symptoms or a family history of bowel cancer should be assessed regardless of age.

If you have had H. pylori, the practical steps are to make sure it was treated and that a repeat test confirmed it had cleared, and to keep up with bowel screening when you reach the recommended age. Do not wait for screening if you notice blood in your stool, black stools, a lasting change in bowel habit, unexplained weight loss or tiredness; see a doctor, who may recommend a colonoscopy (NHS).

Sources

Medically reviewed by Dr Wong Nan-Yaw

MBBS (NUS), FRCS (Edinburgh). 33 years in medicine (since 1993), 23 years as an accredited specialist (since 2003) and 18 years in private practice at Mount Elizabeth (since 2008). Last reviewed 6 November 2026.

How this article is prepared

Statements are checked against the sources listed above. This article is general education and does not replace a consultation. It is reviewed and updated when guidance changes. In an emergency, call 995.