Frequent use of antibiotics may increase the risk of inflammatory bowel disease (IBD) — Crohn’s disease and ulcerative colitis — in people over the age of 40, a new study has shown.

According to the study published in the journal Gut, the risk appears to be cumulative and greatest 1-2 years after use, particularly for antibiotics used to treat gut infections.

In the study, more than 6.1 million people were included, and just over half of them were female.

In total, 5.5 million (91 percent) were prescribed at least one course of antibiotics between 2000 and 2018.

During this period, some 36,017 new cases of ulcerative colitis and 16,881 new cases of Crohn’s disease were diagnosed, according to the study.

Moreover, compared with no antibiotic use, the use of these drugs was associated with a higher risk of developing IBD, regardless of age, but older age was associated with the highest risk.

The study also reveals that those aged 10-40 were 28 percent more likely to be diagnosed with IBD, 40-60 year-olds were 48 percent more likely to do so, while those over the 60s were 47 percent more likely to do so.

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However, the risks were slightly higher for Crohn’s disease than they were for ulcerative colitis — 40 percent among 10-40 year-olds, 62 percent among 40-60 year-olds, and 51 percent among those over the 60s.

As per the age band, the risk seemed to be cumulative, with each subsequent course adding an additional 11 percent, 15 percent, and 14 percent heightened risk, said the study.

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The highest risk of all was observed among those prescribed 5 or more courses of antibiotics — 69 percent heightened risk for 10-40 year-olds, a doubling in risk for 40-60 year-olds, and a 95 percent heightened risk for those over the 60s.

Among 10-40 year-olds IBD risk was 40 percent higher 1-2 years after taking antibiotics compared with 13 percent 4-5 years later.

The equivalent figures for 40-60 year-olds were 66 percent vs 21 percent and for those over the 60s were 63 percent vs 22 percent.

In terms of antibiotic type, nitroimidazoles and fluoroquinolones, which are commonly used to treat gut infections, were associated with the highest risk of IBD, the study mentioned.

These are referred to as broad-spectrum antibiotics because they target all microbes, not just those that cause disease.

Nitrofurantoin was the only antibiotic that was not linked to an increased risk of IBD at any age, the study added.