For the study, researchers examined data on 6.1 million people 10 years and older in Denmark, including 5.5 individuals who received at least one course of antibiotics between 2000 and 2018. During the study period almost 53,000 people were newly diagnosed with IBD, including both Crohn’s disease and ulcerative colitis. Compared with people who never used antibiotics, those who did were significantly more likely to develop IBD at all age groups in the study. With each additional course of antibiotics, the risk of IBD climbed by at least another 10 percent, impacting all ages and rising more for those over 40, according to research published in Gut. Among those 10 to 40 years old, their odds of developing IBD were 28 percent higher, and this increased risk climbed to about 48 percent after age 40. The IBD risk was greatest one to two years after people took antibiotics specifically for gastrointestinal infections, the study also found. “It’s certainly possible that the underlying inflammatory response related to an infection may lead to the associated risk seen,” says lead study author Adam Faye, MD, an assistant professor of medicine and population health at the New York University Grossman School of Medicine. “However, we do have some evidence that antibiotics themselves may contribute to onset of disease.” For example, the study didn’t find any connection between IBD and one antibiotic — nitrofurantoin — which treats urinary tract infections. If the underlying infections could cause IBD then scientists would expect to see an increased risk even when people took nitrofurantoin, Dr. Faye says. The fact that this didn’t happen suggests that the issue is specific to the antibiotics people took, not the underlying infections, Faye adds.
Antibiotic Use Can Have a Detrimental Effect on the Gut Microbiome
While the study wasn’t designed to prove whether or how antibiotics might directly cause IBD, scientists suspect that it may be because they can impact the gut microbiome, the collection of bacteria and other microorganisms that live in your digestive tract and can influence your health. Nitrofurantoin — the antibiotic that doesn’t have much impact on the gut microbiome — was the only one that wasn’t linked to IBD in the study, Faye notes. “The hypothesis, we think, is that antibiotics are altering the intestinal microbiome and leading to the development of IBD,” Faye says. The two types of antibiotics with the highest IBD risk in the study — nitroimidazoles and fluoroquinolones — are both commonly prescribed for gastrointestinal infections. For nitroimidazoles, the increased risk climbed steadily with age and reached 61 percent for those 60 and older. With fluoroquinolones, the increased risk was greatest for people 40 to 60 years old, at 79 percent. One limitation of the study is that researchers lacked data on why antibiotics were prescribed and detailed patient medical information — including whether people had any antibiotics administered during hospital stays. It’s also possible that some people in the study had undiagnosed IBD before they took antibiotics, the authors point out. But the findings add to a growing body of evidence linking antibiotics to an increased risk of IBD. One study of more than 577,000 Danish children, for example, found that kids had a quadrupled risk of Crohn’s disease in the first three months after taking antibiotics. Another study of Swedish adolescents and adults found a more than doubled risk of Crohn’s disease after taking antibiotics and 74 percent higher risk of ulcerative colitis — with the IBD risk rising for each subsequent course of antibiotics. The latest findings support the emerging theory that antibiotics might lead to IBD by destroying beneficial and healthy bacteria that normally lives in the gut, altering the composition of the microbiome or even letting harmful bacteria flourish, says Bincy Abraham, MD, a professor and director of the Fondren Inflammatory Bowel Disease Program at the Underwood Center for Digestive Disorders at Houston Methodist Hospital. This shift in the microbiome may cause inflammation that leads to IBD, says Abraham, who wasn’t involved in the new study. “Antibiotics are quite important if one needs it and can help treat bacterial infections,” Abraham says. “What we do not want to do is to take antibiotics unnecessarily — for example, for a viral infection.” Even the antibiotics with the highest risk of IBD — those that treat gastrointestinal pathogens — are sometimes necessary to avoid sepsis, a potentially fatal bloodstream infection, says Jonas Ludvigsson, MD, PhD, a professor of epidemiology and biostatistics and an IBD researcher at the Karolinska Institute in Stockholm. “I think we should be careful using antibiotics because its use has drawbacks,” says Dr. Ludvigsson, who wasn’t involved in the new study. “But a severe gastrointestinal infection can lead to sepsis, and if one’s physician believes it is indicated, I would not hesitate to take the antibiotics.”
