Antibiotic use is linked to a heightened risk of bowel cancer, according to new research published in the journal Gut.
The findings suggest a pattern of risk that may be linked to differences in gut bacteria activity along the length of the bowel and reiterate the importance of judicious prescribing.
In 2010, patients around the world took an estimated 70 billion doses of antibiotics, equivalent to 10 doses each. Antibiotics have a strong and long lasting impact on the gut microbiome, altering the balance of helpful and harmful bacteria. The researchers wanted to find out if this might affect bowel and rectal cancer risk, and how.
They drew on data submitted to the nationally representative Clinical Practice Research Datalink between 1989 and 2012.
This contains the anonymised medical records of around 11.3 million people from 674 general practices (around 7 per cent of the UK population).
The researchers collected prescribing information for 28,930 patients diagnosed with bowel (19,726 ) and rectal (9254) cancers during an average monitoring period of 8 years, and for 137,077 patients, matched for age and sex, who didn’t develop these cancers.
Antibiotics had been prescribed to 70 per cent (20,278) of patients with bowel and rectal cancers and to 68.5% (93,862) of those without. Nearly six out of 10 study participants had been prescribed more than one class of antibiotic.
Those with bowel cancer were more likely to have been prescribed antibiotics: 71.5 per cent vs 69 per cent. Exposure levels were comparable among those who developed rectal cancer (67 per cent).
The association between bowel cancer and antibiotic use was evident among patients who had taken these drugs more than 10 years before their cancer was diagnosed. Patients who developed bowel cancer were more likely to have been prescribed antibiotics targeting anaerobes, which don’t need oxygen, as well as those targeting aerobes (which do) than patients without cancer.
Cancer site was also associated with antibiotic use. Cancer of the proximal colon (the first and middle parts of the bowel) was associated with the use of antibiotics targeting anaerobes, when compared to people without cancer.
After taking account of potentially influential factors, such as weight, smoking and drinking, cumulative use of antibiotics for a relatively short period (16+ days) was associated with a heightened risk of bowel cancer, with the impact strongest for cancers of the proximal colon.
The researchers conclude: ‘Whether antibiotic exposure is causal or contributory to colon cancer risk, our results highlight the importance of judicious antibiotic use by clinicians.’