Antibiotics linked to increased risk of inflammatory bowel disease, research shows

Those aged 40 and older most likely to suffer side effect, study examining 18 years of data finds

Taking antibiotics is linked with an increased risk of inflammatory bowel disease (IBD), with new research indicating those aged 40 and older are most vulnerable.

The new study, published on Monday, examined 18 years of data and also found the risk of disease increased with each subsequent antibiotic course, and was highest following exposure to antibiotics commonly prescribed to treat gastrointestinal infections.

Experts here welcomed the research and said it would better inform clinicians and patients about the potential risks of using certain antibiotics, particularly in older people – even though there is often little choice but to prescribe the medication.

The research is published in Gut, a specialist journal issued by the British Medical Journal, and is based on national medical data from 2000 to 2018 for Danish citizens aged 10 and upwards who had not been diagnosed with IBD.


Some 5.5 million people had been prescribed at least one course of antibiotics during the study period and follow-up analysis revealed 36,017 new cases of ulcerative colitis and 16,881 new cases of Crohn’s disease were diagnosed.

“Overall, any antibiotic exposure was associated with an increased risk of IBD for all age groups compared with individuals with no antibiotic exposure,” it said, adding that the risk increased with age, with those between 40 and 60 years of age 48 per cent more likely to develop IBD.

“The highest risk was among individuals receiving five or more courses of antibiotics, and held true for all age groups,” it said. It also found the highest risk for developing IBD was one to two years after antibiotic exposure.

The only class of antibiotics not found to be associated with the development of IBD across all age groups was nitrofurantoin, while the highest risk was associated with nitroimidazoles and fluoroquinolones, which treat a range of bacterial infections.

Prof Anthony O’Connor, head of the department of gastroenterology at Tallaght University Hospital, said: “We know that around 40 per cent of the risk of IBD is inherited but we do not really know what makes up the other 60 per cent.

“We know that antibiotics interfere with the gut flora,” he said, adding that the “big question” was whether those antibiotics could trigger IBD, which he said was “elusive to diagnosis”.

Prof O’Connor said there were 3,000 IBD patients in Tallaght hospital alone and the ideal situation would be “better non-invasive testing”, adding: “Where we want to get to is identifying people at risk of IBD at a young age. We are not there yet but we are getting there.”

IBD affects seven million people worldwide and Dr Brian Egan, consultant gastroenterologist and acute medical physician at Mayo University Hospital, warned last year of a significant rise in IBD cases Ireland, where it is estimated to affect 40,000 people.

He echoed Prof O’Connor’s views and said there had been “huge improvements” in antimicrobial stewardship in recent years with clinicians acutely aware of the risks associated with prescribing antibiotics.

“Overall it is a very good study in at least being able to inform patients about the risk of using antibiotics that we often have no choice but to use,” he said.

“The thing that we also try to do is inform the patient of the risk and this is potentially another risk in using these antibiotics, especially in older people.”

Amy Kelly, head of communications and fundraising with Crohn’s and Colitis Ireland, said the organisation had seen a 400 per cent increase in the number of people contacting its helpline during the Covid-19 pandemic.

Ms Kelly said giving GPs a better understanding of the potential need for referral to a specialist could prevent emergency trips to emergency departments.

“It is not atypical for someone living with IBD to take between one to two years to get diagnosed with the illness,” Ms Kelly said. “Often the diagnosis comes from a hospital admission when the illness becomes critical.”