But the risk is highest in people over 40 in the first two years after taking antibiotics, researchers say.
Taking antibiotics may increase the risk of inflammatory bowel disease, especially in people over 40, research suggests.
The risk is highest within one to two years of using antibiotics but begins dropping after that, according to an analysis of Danish data over 19 years published in Gut.
“The risk of inflammatory bowel disease was greatest among individuals aged 40 years and older, increased with each subsequent antibiotic course, and was highest following exposure to antibiotic groups commonly prescribed to treat gastrointestinal pathogens,” the Danish and US researchers said.
The researchers said the increased risk was observed for both ulcerative colitis and Crohn’s disease.
“The highest risk was among individuals receiving five or more courses of antibiotics, and held true for all age groups,” they said.
The researchers found that people aged 40 to 60 had a 66% higher risk of developing inflammatory bowel disease within one to two years of exposure to antibiotics. People over 60 had a 63% increased risk, while the risk was 40% higher for those aged 10 to 40.
The observational study included data on 6 million Danes, 90% of whom were prescribed at least one course of antibiotics between 2000 and 2018.
During that period there were 6,000 new cases of ulcerative colitis and 17,000 new cases of Crohn’s disease.
The researchers said nitroimidazoles and fluoroquinolones had the highest association with inflammatory bowel disease.
But they said nitrofurantoin, which had less impact on the gastrointestinal flora, was not associated with the risk of inflammatory bowel disease.
The study authors referred to a recent study comparing the microbiome of healthy older and younger adults, where older adults were found to have decreased abundance of Bifidobacterium, which is also reduced in patients with inflammatory bowel disease.
“These 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,” they wrote.
“The association between antibiotic exposure and the development of inflammatory bowel disease underscores 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 adults.”
Australian gastroenterologist Professor Jon Watson said the size of the study population and the quality of the data meant the study was robust.
“It’s a good study, and there are limitations, but I think it’s an important step on the journey as we understand more about the microbiome and its association with these two diseases,” said Professor Watson, from University Hospital Geelong.
“And it might tell us more about the microbiome and strategies for trying to help our patients with Crohn’s disease and ulcerative colitis,” he added.
Professor Watson said it was already known that there was a reduction in diversity of the microbiome in older patients.
“If you’re over 40 and your microbiome is already reduced, and then you take antibiotics, maybe that’s what flicks the switch and turns it off.”
Professor Watson said there had been previous studies examining the link between the microbiome and inflammatory bowel disease, but this study included a larger population and looked at one to four courses of antibiotics.
“The 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?
“There have been studies around that, but to my knowledge, I don’t think there’s a direct equivalent to the Danish study, which is why it’s so interesting.”