Could a Common Stomach Infection Be Linked to Bowel Cancer?

A bacterium that commonly causes stomach infections may be associated with a greater risk of bowel cancer, according to a large analysis of previous research.

The bacterium, Helicobacter pylori, usually known as H. pylori, is widespread around the world. Many people acquire the infection during childhood and never develop noticeable symptoms. In some cases, however, it can cause inflammation of the stomach lining, ulcers and other digestive problems.

The new research has drawn attention because H. pylori has long been recognised as an important cause of stomach cancer, while its possible relationship with colorectal cancer has remained uncertain.

Researchers behind the latest analysis say their findings add to evidence suggesting that the infection could play a role in bowel cancer. However, they also stress that more research is needed before scientists can establish whether the bacterium directly causes the disease or whether eliminating the infection can prevent bowel cancer.

What is H. pylori?

H. pylori is a type of bacterium that can live in the digestive system, particularly in the stomach. It is one of the most common bacterial infections affecting humans.

According to Guts UK, as many as two in five people in the UK may carry the bacterium. Despite its prevalence, infection does not necessarily mean that a person will become seriously ill.

Some people have no symptoms at all. Others may experience problems such as stomach pain, indigestion or ulcers. Long-term infection can cause persistent inflammation in the stomach and is an established risk factor for stomach cancer.

The bacterium can spread through contact with bodily fluids, including saliva, vomit and stool. Infection frequently occurs earlier in life.

What did the researchers discover?

An international research team, involving scientists from the University of Hong Kong and the University of California San Diego, examined evidence from previous studies investigating the relationship between H. pylori and colorectal cancer.

The researchers combined findings from 43 studies involving more than 48 million people with cancer data from the Global Cancer Observatory.

Their analysis found that people exposed to H. pylori had an estimated 1.59 times higher risk of colorectal cancer than people who had not been exposed.

The researchers then used the available evidence to estimate how many colorectal cancer cases could potentially be associated with the infection.

Under the study's assumptions, they estimated that approximately 22 per cent of colorectal cancer cases worldwide could be related to H. pylori exposure.

That figure is potentially significant, but it needs to be interpreted carefully.

An association between an infection and a disease does not automatically prove that the infection directly caused the disease. Other factors may contribute to the observed relationship, and researchers need high-quality prospective studies to determine whether removing the bacterium actually lowers cancer risk.

Could treating the infection reduce cancer risk?

One particularly interesting part of the research involved studies examining what happened after H. pylori was eliminated using antibiotics.

Only four studies included in the analysis investigated eradication of the infection and subsequent colorectal cancer risk. Their findings suggested that removing the bacterium could potentially reduce the risk of bowel cancer.

However, any possible benefit appeared to take a considerable amount of time to emerge.

The research indicated that a reduction in risk may not become apparent until 10 years or more after eradication.

Because the number of studies examining eradication was small, the researchers said further investigation is needed before conclusions can be drawn about whether treating H. pylori can prevent colorectal cancer.

Why might the infection matter?

Scientists are still investigating the biological mechanisms that could connect H. pylori with colorectal cancer.

One possibility is that long-term infection and inflammation could influence processes elsewhere in the digestive system. Chronic inflammation can affect tissues over time and is known to be involved in the development of several diseases.

However, the precise relationship between H. pylori, the gut environment and colorectal cancer remains an area of active research.

The researchers also examined whether the potential association varied between different generations. Their analysis suggested that the proportion of colorectal cancers potentially linked to H. pylori was higher among people born in more recent periods than among the oldest group examined.

These findings may provide researchers with additional clues about changing patterns of infection and cancer risk.

What are the warning signs of bowel cancer?

Regardless of the findings about H. pylori, people should be aware of possible symptoms of bowel cancer.

The NHS says symptoms can include a persistent change in bowel habits, such as diarrhoea or constipation that is unusual for you. Other possible warning signs include blood in the stool, bleeding from the bottom, unexplained weight loss, abdominal pain, bloating and unusual tiredness.

Some people may also experience a persistent feeling that they need to have a bowel movement even after going to the toilet.

These symptoms can have many causes and do not necessarily mean that someone has cancer. Nevertheless, persistent or unusual changes should not be ignored, particularly if they continue or become worse.

Early diagnosis can make an important difference in cancer treatment, which is why medical advice should be sought when concerning symptoms develop.

Does this mean everyone should be tested for H. pylori?

Not necessarily.

The new research does not establish that everyone carrying H. pylori will develop bowel cancer, nor does it show that testing and treating every infected person will prevent colorectal cancer.

The authors themselves called for further high-quality research, particularly prospective studies that follow people over a long period. Such research could help determine whether eradication of H. pylori actually reduces colorectal cancer risk.

For now, the findings are best understood as evidence of a potentially important association rather than proof of a new cause of bowel cancer.

The research could nevertheless have implications for future cancer-prevention strategies, especially in countries and communities where H. pylori infection is particularly common.

A potentially important area of research

Bowel cancer is influenced by a complex combination of factors, including age, genetics, lifestyle and environmental exposures. The possibility that a common bacterial infection could contribute to some cases offers scientists another potential avenue for prevention.

The latest analysis is notable because of its enormous combined sample size. More than 48 million people were represented across the studies reviewed.

At the same time, the researchers' conclusions underline an important distinction between identifying a statistical association and proving causation.

Future studies will need to establish whether H. pylori directly contributes to the development of colorectal cancer and whether eliminating the infection can meaningfully reduce that risk over the long term.

Until then, people should not interpret the findings as a reason to panic. Anyone concerned about digestive symptoms or possible H. pylori infection should discuss their concerns with a qualified healthcare professional.

Source

eGastroenterology, alongside information from the NHS, Guts UK and the Global Cancer Observatory.

Disclaimer

This article is provided for general information and educational purposes only. It is not medical advice and should not be used to diagnose, treat or prevent any illness. The research discussed describes an association between H. pylori exposure and colorectal cancer and does not, by itself, prove that the infection causes bowel cancer. Speak with a qualified healthcare professional if you have persistent symptoms or concerns about your health.