Helicobacter pylori — the common stomach bacterium best known for causing ulcers and gastric cancer — is increasingly being linked to colorectal cancer (CRC) too. But the science is a case study in why “linked to” is not the same as “causes.”
What the evidence shows
Many observational studies and recent meta-analyses report an association between H. pylori infection and higher CRC risk (and its precursor, adenomas). H. pylori infects roughly half the world’s population, so even a modest risk increase would matter at scale. Plausible mechanisms include chronic inflammation and shifts in gut hormones and the microbiome.
Why it’s unsettled
The crucial open question is whether eradicating H. pylori lowers CRC risk — and here the data conflict. A 2026 population-based study found CRC incidence and mortality were lower in treated individuals than in the general population. Yet a large Swedish nationwide cohort found eradication was associated with an elevated risk of colorectal adenocarcinoma. With few randomized controlled trials, a causal link can’t be established either way.
Why it matters
H. pylori testing and eradication are already routine for stomach-related reasons, and this growing body of work is a reason to keep studying the colon connection — not yet a reason to treat the bug specifically to prevent colon cancer. The honest status: a real and strengthening association, an unresolved treatment question. This summarizes research and is not medical advice; screening decisions belong with your doctor.