Study Links Common Stomach Bacteria to 22% of Bowel Cancer Cases Worldwide, But Researchers Call the Connection 'Highly Controversial'

The Numbers

An international team led by researchers at the University of Hong Kong and the University of California San Diego published an analysis in the journal eGastroenterology estimating that exposure to Helicobacter pylori, the bacteria behind a common stomach infection, may be linked to as many as 22% of bowel cancer cases worldwide.

The study found people exposed to H. pylori had a 1.59-fold higher risk of bowel cancer compared to those never exposed, according to The Independent and MSNBC, which both carried identical accounts of the findings. News Medical reported the figure slightly rounded, at 1.6-fold.

The researchers pooled data from 43 prior studies covering more than 48 million people, then combined that with global cancer figures from the Global Cancer Observatory (GLOBOCAN) for 2022. Worldwide, bowel cancer, also called colorectal cancer, killed roughly 900,000 people and produced nearly 2 million new diagnoses that year, according to News Medical.

The Caveat Missing From Most Coverage

When the researchers narrowed their analysis to just the 14 highest-quality, population-based and cohort studies, the estimated share of bowel cancer cases linked to H. pylori dropped to 12%, according to News Medical's report on the paper. That's roughly half the headline 22% figure.

The 22% number comes from pooling all 43 studies, including weaker study designs. The 12% figure comes from the studies researchers themselves consider more reliable. Readers getting this story only from the outlets that led with 22% never saw that number cut in half under stricter methodology.

The study's authors were upfront that the H. pylori-bowel cancer link remains "highly controversial," according to The Independent and Express, and separately described it as "hotly debated" in the News Medical account. H. pylori is already classified as a definite (Group 1) carcinogen for stomach cancer specifically. Its role in bowel cancer is a different, less-settled question.

What the Data Actually Shows

The researchers broke results down by birth year. Bowel cancers were linked to H. pylori exposure in 9.5% of cases among people born before 1947, 10.2% among those born 1948-1962, and 15% among those born 1963-1977, according to The Independent and Express. That upward trend by birth cohort is an observed pattern, not a proven cause.

Geographically, the Western Pacific region and Mongolia showed the highest estimated proportions of cases tied to H. pylori, at 25% and 36% respectively, while China had the highest raw number of linked cases at 139,619, according to News Medical. Notably, Africa, South-East Asia and the Eastern Mediterranean have similarly high H. pylori infection rates but far lower estimated shares of bowel cancer attributable to it, an inconsistency the researchers didn't fully explain.

On treatment, only four observational studies in the entire analysis actually tracked whether eradicating H. pylori with antibiotics changed bowel cancer risk. Those four suggested a reduced risk, but only showed up after 10 years, according to both The Independent and Express.

The Honest Read

About 40% of people in the UK carry H. pylori in their stomachs, according to the charity Guts UK, most without symptoms. It typically spreads through contact with an infected person's saliva, vomit or stool, often picked up in childhood.

The study's own authors wrote that "high-quality, prospective studies with long-term follow-up are warranted to clarify whether H. pylori eradication causally reduces CRC risk," as quoted by The Independent, Express and MSNBC. In doing so, they acknowledged that this paper establishes an association, not proof that killing the bacteria prevents cancer.

No public health agency has issued new screening or treatment guidance based on this analysis. Future prospective trials tracking people who get treated for H. pylori against those who don't may show lower bowel cancer rates over time. Until that data exists, the 22% figure is an estimate under what the authors themselves call "a causal assumption," not a confirmed cause.