A leading oncologist has warned that a common stomach infection acquired in childhood may have an unexpected link to bowel cancer. A new study suggests that exposure to Helicobacter pylori (H pylori) could be associated with more than one in five cases of bowel cancer across the globe.
Professor Justin Stebbing, Professor of Biomedical Sciences at Anglia Ruskin University, described this as a striking figure, particularly given how widespread H pylori is. He said: "The wider significance of this research may be what it tells us about the causes of cancer. We tend to think of bowel cancer mainly in terms of genes, ageing and lifestyle. But some cancers also have an infectious component."
"The possibility that an infection acquired in childhood could influence the risk of bowel cancer decades later therefore deserves serious investigation."
What is H pylori?
The NHS says H pylori is a type of bacteria that can infect the lining of the stomach and the first part of the small intestine. One NHS trust says: "Around 40% of people in the UK have H. pylori in their stomach. For most, it causes no problems at all and doesn’t require treatment. Only around 1 in 10 people with H. pylori will experience symptoms or complications."
The professor stressed that the study does not prove H pylori causes bowel cancer, but rather estimates how many bowel cancer cases might be connected to the infection. Bowel cancer, also known as colorectal cancer, develops in the colon or rectum and is among the most commonly diagnosed cancers worldwide, affecting approximately 1.9 million people every year.
Risk factors for bowel cancer
He noted that several risk factors for bowel cancer are already well established, including advancing age, family history, smoking, obesity, alcohol consumption and diets rich in processed meat. However, researchers are increasingly focusing on another potential contributing factor: the trillions of microorganisms residing in our digestive system, known as the microbiome, and the infections that can disrupt this delicate environment.
Writing in The Conversation, the professor, who specialises in oncology and cancer research, highlighted H pylori as a particularly compelling candidate. Not only has the bacterium evolved to survive in the stomach's highly acidic conditions, but it is also already known to trigger gastric cancer.
He said: "It's thought around half of the world's population are infected with H pylori– although rates vary greatly between countries. Infection often occurs during childhood."
"Most infected people never develop symptoms. But in some, H pylori causes long-term inflammation of the stomach lining. This can lead to ulcers and, in a small proportion, stomach cancer. The evidence that H pylori causes cancer is strong enough that it's classified as a carcinogen. But the bacterium's relationship with bowel cancer is less clear."
What the study found
Previous studies have shown that people infected with H pylori have a higher risk of developing colorectal cancer. The latest study attempted to contextualise these findings. It gathered data from 43 studies involving almost 49 million people and combined it with information about the prevalence of both H pylori and bowel cancer globally.
He said: "Overall, people exposed to H pylori had about a 1.6 times greater risk of being diagnosed with bowel cancer compared to those without evidence of infection. Using these figures, the researchers calculated that approximately 22% of bowel cancers worldwide could be associated with H pylori."
"This doesn't mean H pylori has been shown to cause one in five bowel cancers. The calculation depended heavily on the studies included – and, crucially, assumes that at least some of the observed association is causal."
He added that when the researchers narrowed their analysis to 14 population-based and cohort studies — designs generally considered more reliable for examining how risk develops over time — the estimated proportion of bowel cancers linked to H pylori dropped to around 12%.
The professor noted it is also conceivable that some of the apparent connection reflects other distinctions between those who contract H pylori and those who don't – including diet, smoking, physical activity levels, socioeconomic conditions and healthcare access. He continued: "Nevertheless, there are several plausible ways H pylori might influence bowel cancer."
What happens when H pylori infection is treated
H pylori may also have an impact on hormones and other molecules involved in digestion and cell growth. While a fascinating possibility, there is currently no evidence of the chain of events that leads from a stomach infection to cancer in the colon or rectum.
The professor said: "Perhaps the most interesting finding from the study concerns what happens when the infection is treated. H pylori can usually be eradicated using a combination of antibiotics and medicines that suppress stomach acid. Across four observational studies included in the analysis, people who received treatment for H pylori appeared to have a lower subsequent risk of bowel cancer – with the difference becoming apparent after ten years."
Yet he said these were observational studies, not trials in which people were randomly assigned to treatment or no treatment, so we cannot yet conclude that eliminating H pylori prevents bowel cancer. He asked: "So should people now ask to be tested for H pylori to reduce their bowel cancer risk?"
"On the evidence available today, no. We need stronger evidence showing that detecting and treating H pylori actually reduces colorectal cancer incidence."
Best ways to lower bowel cancer risk
He stressed that, currently, the most effective methods of reducing your bowel cancer risk remain those backed by robust evidence. This encompasses bowel cancer screening, which can detect cancers at an earlier, more treatable stage and can occasionally prevent cancer by identifying and removing precancerous growths known as polyps.
Keeping a healthy weight, staying physically active, not smoking, moderating alcohol consumption and cutting down on processed meat can also lower the risk. Warning signs such as blood in the stool, a persistent change in bowel habits, unexplained weight loss or prolonged abdominal discomfort should never be ignored, although they are frequently brought about by conditions unrelated to cancer.
NHS symptoms list for bowel cancer
The NHS website lists a number of symptoms to be aware of:
- needing to poo more or less often than is usual for you
- often feeling like you need to poo, even if you've just been to the toilet
- tummy pain
- bloating
- changes in your poo, such as having softer poo, diarrhoea or constipation that is not usual for you
- blood in your poo, which may look red or black
- losing weight without trying
- feeling very tired or short of breath – these are signs of anaemia, which can be caused by bowel cancer
- bleeding from your bottom
- a lump in your tummy
For more information, visit the NHS website. The Conversation website is updated regularly with articles on health, science and many other topics.
