The role of bacteria in colon cancer


You’ve probably heard a lot of stories about what causes colon cancer. In the press these are usually overly simplified and horribly misleading. They often leave you thinking that it’s your fault you got cancer because you ate something you shouldn’t or didn’t eat something you should.

The truth is that while doctors can sometimes tell you why you got colon cancer – eg if you have a dodgy gene – in most cases they’re still not really sure. Colon cancer is largely a disease of age, and of wear and tear, so eating a good diet, exercising and not smoking all help to reduce your lifetime risk but that doesn’t mean they eliminate your risk.

In fact, many people who have colon cancer find themselves asking: but hang on a minute I do have a good diet and I’ve never smoked and I exercise. What’s going on? The answer is that we still don’t know.

Often, doctors cannot tell you why you got colon cancer – so you just have to learn to live with not knowing – which can be a difficult thing to do. But scientists are trying hard to find out why colon cancer occurs so that they can stop people from getting it.

The increasing number of young people getting colon cancer suggests a change in lifestyle factor may be at play. But so many things have changed in the way people live in the last 50 years, where do we start looking?

One thing that seems to be important is gut health. A study from Johns Hopkins University led by Cynthia Sears (published in Nature), found that certain bacteria seem to invade the mucus that protects the surface of the colon. The researchers found e-coli and bacteroides fragilis were the two species dominating these patches of invasive bacteria. Each of these carries a gene for a cancer-promoting toxin.

Another culprit that’s been implicated is streptococcus gallolyticus gallolyticus (SGG) which has been found to cause tumour growth in mice and has been found in colon tumours. Research by Yi Xu at the Texas A&M Health Science Center found that mice fed SGG developed twice the volume of tumours as those fed a different microbe. Human colon cancer cells also multiplied faster when SGG was present. And the team found that 74% of tumour samples from colon cancer patients had SGG bacteria in them – 26% had very high levels.

Meanwhile, researchers from the University of Michigan and Baylor College of Medicine found that when healthy mice were exposed to faecal matter taken from mice with colon cancer, they doubled their chance of developing tumours. Treating the mice with antibiotics reduced the number and size of the tumours.

Another study published in the Journal of the National Cancer Institute showed that colon cancer patients had more fusobacteria than healthy patients. They were also had less of the beneficial bacteria clostridia, which helps with digestion.

Clearly, there is still a lot of work to do, but an increasing number of studies are pointing to the fact that having the wrong kind of bacteria in your gut, or the wrong balance of bacteria, increases your risk of developing colon cancer.

This would explain why there is a link to diet, although diet doesn’t wholly explain what’s going on. This is because diet may turn out to be not the causal agent but an indirect influencer that affects gut health, along with your environment, antibiotic use and hormones.

If gut health is important to preventing colon cancer, this points to fairly low-tech and cheap methods to beat this killer and prevent its recurrence. It means eating a good, varied diet, avoiding unnecessary antibiotics (and if you have to take them ensuring you recolonize your gut with good bacteria via probiotics), getting plenty of rest and managing your stress. Fermented foods such a yogurt, kefir, sauerkraut, kimchi, sourdough and homemade pickles can also help.

If bacteria do turn out to be major agents in colon cancer then judicious use of probiotics and antibiotics could be the way forward. Food for thought eh?

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