Middle-aged and older patients appear most at risk, and the chances are highest in the first two years after taking antibiotics.
Taking antibiotics may increase the risk of inflammatory bowel disease, especially in people over 40, research suggests.
There also appears to be a dose-response relationship, with the risk of developing inflammatory bowel disease increasing with subsequent antibiotic courses.
âThe highest risk was among individuals receiving five or more courses of antibiotics, and held true for all age groups,â the authors wrote in Gut.
The analysis of two decades of Danish health data found that 90% of participants were prescribed at least one course of antibiotics in that period. The chances of developing inflammatory bowel disease were highest after patients were treated with antibiotics commonly used against gastrointestinal pathogens, and the link was found for both ulcerative colitis and Crohnâs disease.
Such a link âunderscores the importance of antibiotic stewardship as a public health measure, and suggests the gastrointestinal microbiome as an important factor in the development of inflammatory bowel disease, particularly among older adultsâ, the authors wrote.
Age appeared to play an important role; people aged 40 to 60 had a 66% greater chance of developing inflammatory bowel disease within one to two years of exposure to antibiotics, compared to those who hadnât been exposed in the two-decade study period.
People over 60 had a 63% increased risk, and people aged 10 to 40 had a 40% increased risk.
The study authors pointed to recent research showing older adults has less of an abundance of Bifidobacterium in their gut microbiome, which is also reduced in patients with inflammatory bowel disease, compared to younger adults.
âThese aging-related changes can be compounded by antibiotic use, which further deprives the gut microbiome of diversity, and has the potential to lead to longstanding microbial changes,â they wrote.
Australian gastroenterologist Professor Jon Watson said the size of the study population and the quality of the data meant the study was robust.
Researchers have already found evidence that the diversity of the microbiome drops in older patients.
âIf you’re over 40 and your microbiome is already reduced, and then you take antibiotics, maybe that’s what flicks the switch,â said Professor Watson, from University Hospital Geelong.
This study was larger than previous studies exploring the microbiome and inflammatory bowel disease and drilled into the effects of different courses of antibiotics, said Professor Watson.
âThe obvious extension to this is if there’s a change in the microbiome which causes one of these diseases, how can we help our patients to try and reverse the changes in the microbiome?â
During the study period, there were 6000 new cases of ulcerative colitis and 17,000 new cases of Crohnâs disease.
Antibiotics associated with the highest risk were nitroimidazoles and fluoroquinolones. But nitrofurantoin, which has less impact on the gastrointestinal flora, was not tied to inflammatory bowel disease.
