A bacterium that can reside in the stomach for decades, Helicobacter pylori (H pylori), may have an unexpected connection with bowel cancer. A recent study estimates that exposure to this bacterium could be associated with more than 22% of bowel cancer cases globally. While this figure is striking, the study does not definitively prove causation, but rather estimates the potential link.
Bowel cancer, also known as colorectal cancer, affects approximately 1.9 million people annually worldwide. Known risk factors include older age, family history, smoking, obesity, alcohol consumption, and diets high in processed meat. Researchers are increasingly investigating the role of the gut microbiome and infections, such as H pylori, in cancer development.
H pylori is a notable candidate as it is known to cause gastric cancer and is adapted to survive in the stomach's acidic environment. It is estimated that around half of the world's population is infected, often during childhood, though most individuals remain asymptomatic. In some cases, H pylori leads to long-term inflammation of the stomach lining, potentially causing ulcers and, in a small percentage, stomach cancer. Its classification as a carcinogen is well-established.
Previous studies have indicated a higher risk of colorectal cancer in individuals infected with H pylori. The latest research analysed data from 43 studies involving nearly 49 million people. It found that those exposed to H pylori had approximately a 1.6 times greater risk of being diagnosed with bowel cancer. When the analysis was restricted to more robust study designs, the estimated proportion of bowel cancers associated with H pylori fell to about 12%.
The observed association may also reflect other differences between infected and uninfected individuals, including diet, smoking habits, physical activity, socioeconomic conditions, and healthcare access. Plausible mechanisms for H pylori influencing bowel cancer include chronic inflammation, which can alter cell growth signals, and changes to the gut microbiome affecting chemical production in the bowel.
Interestingly, some studies suggest that treatment for H pylori may be associated with a lower subsequent risk of bowel cancer, particularly after 10 years. However, these observational findings require further confirmation through randomised controlled trials to establish a causal link.
Currently, the most effective strategies for reducing bowel cancer risk remain evidence-based. These include regular screening, maintaining a healthy weight, physical activity, limiting alcohol and processed meat intake, and not smoking. Prompt medical attention for symptoms like blood in the stool or persistent changes in bowel habits is also crucial.
This research highlights the potential infectious component in the causes of some cancers, suggesting that infections acquired in childhood could influence cancer risk decades later, warranting further investigation.
