The little-known toxin that could be behind the rising rates of bowel cancer in under-50s
Cases among the under-50s have shot up by 22 per cent over the last few decades too. Now every year, more than 2,600 people in this age group are told they have bowel cancer.
The reason behind the surge remains unknown. Our sedentary lifestyles, the rise in obesity, heavy drinking and low-fibre, high-fat diets are some of the reasons that scientists have put forward as contributing factors.
Now, a study suggests that exposure to a toxin in childhood – called colibactin and produced by certain strains of E. coli – could, at least in part, be fuelling the surge. Here's what you need to know.
Escherichia coli (E. coli) bacteria is commonly found in our guts. Most strains are harmless and some, such as Nissle 1917 (EcN) are even beneficial and aid in digestion.
However, others, such as pks+ E. coli, release toxins that may cause bowel cancer. Scientists don't yet know how these 'bad bug' make there way into our gut or how we can avoid them. Additionally, they may not be harmful in all cases and some strains that produce toxins are even used in probiotics.
Outside of a research study, it's not currently possible to tell whether the bacteria in your gut are producing harmful toxins that could raise your bowel cancer risk.
Certain strains of E. coli produce a bacterial toxin called colibactin. This is thought to be a defence mechanism to protect itself from other bacteria, explains Dr Paul Brennan, who runs the genetics section at the International Agency for Research on Cancer.
Colibactin can damage the DNA in our bowel cells by introducing mutations, adds Justin Stebbing, an oncologist and professor of biomedical sciences at Anglia Ruskin University.
The DNA damage caused by colibactin leaves a trail of mutations that scientists have previously found in 10 to 15 per cent of all bowel cancer cases.
But the new study, published in the journal Nature, strengthens this link, suggesting that exposure to colibactin in early childhood by the age of 10 sets the stage for cancer, long before symptoms arise.
Scientists led by the University of California San Diego analysed nearly 1,000 bowel cancer genomes and found that mutations caused by colibactin were 3.3 times more common in patients who developed bowel cancer before they turned 40, compared to those who developed the disease after the age of 70.
'This suggests a strong link between colibactin exposure and early onset bowel cancer,' says Dr Vivian Li, the group leader of the Stem Cell and Cancer Biology Laboratory at the Francis Crick Institute.
'The latest research on this shows a clear correlation, especially in younger people, between colibactin and the production of mutations that potentially caused bowel cancers to grow,' adds Prof Trevor Graham, the director of the Centre for Evolution and Cancer at The Institute of Cancer Research.
'There is more work to do to really prove that colibactin is responsible for the increase that we're seeing in early onset bowel cancer, but we should be looking very hard at the link with colibactin producing bugs going forward,' Prof Graham adds.
However, it may be that colibactin is just one part of the jigsaw puzzle of risks fuelling the rise in bowel cancer among young people, Prof Stebbing notes. 'I'd describe it as a potential culprit. We just can't say it's causative,' he says.
Scientists don't yet know how children are being exposed to colibactin-producing bacteria, so it isn't yet clear what actions will reduce the risk of it taking hold in your gut.
'We are working to try to understand exactly when these mutations occur,' says Dr Brennan, who is also co-investigator for Cancer Research UK's Cancer Grand Challenges, which funded the research.
'If they occur within the first weeks of life then this would implicate exposures around childbirth and weaning. This is when the infant microbiome is formed. Conversely, if they occur later in infancy, this could implicate dietary sources.'
'We just don't know yet what might disrupt the natural bacteria in the gut early in life to lead to growth of these strains of bacteria that produce colibactin,' Prof Stebbing adds.
However, Dr Li notes that contaminated food and untreated water can contain these bacteria, so improving food safety and hygiene may help minimise exposure.
And some colibactin-producing bacteria are used in probiotics, she notes. 'More research would be needed to address the safety [of this],' she adds.
The researchers behind the latest study are now investigating potential sources – such as diet, the environment and lifestyle behaviours – and what can be done to prevent or mitigate that contact with these bugs.
It's also not currently possible to find out whether you have worrying mutations caused by the bacterial toxin.
'This is very much laboratory based research just now, and there's no routine test for it,' Prof Stebbing explains. However, the researchers are currently developing an early detection test to analyse stool samples for colibactin-related mutations.
But, even if these tests become available, it is unclear what can be done to reduce the risk of bowel cancer occurring. 'We don't have a treatment available, or know if removal of the bugs would be beneficial to prevent bowel cancer, or even if there could be other unintended consequences,' notes Prof Graham.
The researchers are exploring whether probiotics could safely eliminate harmful bacterial strains from the gut, which produce colibactin. In the meantime, there are plenty of other actions that can dramatically lower your bowel cancer risk.
Adding more fibre to your diet – such as by eating plenty of fruit, vegetables, legumes and wholegrains – can drive down the chance of developing the disease because it helps to keep bowel movements regular, meaning harmful chemicals in stools spend less time in the bowel.
Additionally, fibre interacts with bacteria in the gut to make butyrate, which helps keep the cells in the bowel healthy, reducing the risk of tumours developing. More than a quarter (28 per cent) of bowel cancer cases are caused by not consuming enough fibre.
Limiting red and processed meat intake can help to reduce your risk of bowel cancer. Around 13 per cent of bowel cancer cases in the UK are linked to having too much of it in our diet because the foods contain substances such as nitrates and nitrites, which damage the cells in the bowel.
Obesity is another cause of bowel cancer (estimated to be behind 11 per cent of cases) so losing weight by eating a balanced diet and exercising more can help to reduce your risk.
'Being physically active and cutting back on alcohol are also changes you can make to reduce bowel cancer risk,' says Sophia Lowes, a senior health information manager at Cancer Research UK.
'No matter how old you are, if you notice anything that isn't normal for you, don't ignore it, speak to your doctor. In most cases it won't be cancer, but if it is, spotting it early can make a real difference.'
Symptoms of bowel cancer include changes in stools – such as having softer stools, diarrhoea or constipation that is not normal for you – needing to go to the toilet more often and blood in the stool.
'Whatever your age, it's important that you contact your GP and ask for an at-home test if you spot any symptoms,' says Dr Lisa Wilde, director of research, policy and influencing at Bowel Cancer UK. 'Bowel cancer is treatable and curable especially if diagnosed early.'
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