With commentary by Kristian Hallundbæk Mikkelsen, lead study author and a PhD student at the Center for Diabetes Research at Gentofte Hospital and the University of Copenhagen in Denmark
A new study found an increased incidence of type 2 diabetes in people who took more antibiotics. The authors caution that the study does not show whether the antibiotics increase the risk of diabetes or that the findings reflect the fact that people with diabetes have a higher incidence of infections and therefore take more antibiotics.
The new study, conducted in Denmark, looked at more than 170,500 Danes with type 2 diabetes and a control group of more than 1.3 million. The researchers examined the use of all systemic antibiotics between January 1, 1995, and July 1, 2012.
The study, published in the Journal of Clinical Endocriniology & Metabolism, found that patients treated for type 2 diabetes filled on average 0.8 antibiotic prescriptions per year compared to 0.5 prescriptions per year among controls. The more antibiotics someone took, the more likely they were to have diabetes. Those that filled 2 to 4 prescriptions of antibiotics of any type had a 53% increased risk of having type 2 diabetes than those who filled 0 to 1 prescriptions of antibiotics. Slightly higher risks were found for narrow-spectrum antibiotics (like penicillin) compared with broad-spectrum antibiotics, such as fluorquinolones or tetracyclines.
But it isn’t clear what is behind the association. People with diabetes are more susceptible to infections and may naturally take more antibiotics, and there was certainly a chance that people had undiagnosed diabetes or even prediabetes prior to being treated. The authors tried to control for this by excluding antibiotic prescriptions filled less than 6 months before the time when patients were treated with a non-insulin glucose lowering medicine (the authors used this point to determine diabetes rather than date of diagnosis). They also did another analysis, going back three years and found that the risk was slightly lower but still significant.
They did a further analyses that found that antibiotic exposure was increased among those with diabetes up to 15 years earlier, which the authors said was not likely to be caused by increased susceptibility to infections caused by prediabetes or undiagnosed diabetes.
“It is commonly accepted that patients with diabetes have an increased risk of acquiring infections and as a consequence also have a higher demand for antibiotics,” says Kristian Hallundbæk Mikkelsen, the study’s lead author and a PhD student at the Center for Diabetes Research at Gentofte Hospital and the University of Copenhagen in Denmark. “At the same time a number of animal studies have suggested that antibiotics may change glucose and lipid metabolism upon altering the gut bacteria composition of the animal.”
But the authors said more research was needed to determine whether it was a causal link. “The possibility that antibiotics exposure increases diabetes risk cannot be excluded and deserves further investigation in interventional studies,” the authors wrote in the study.
“I don’t think that our study justifies any public recommendations about use of antibiotics, but there are already many good reasons not to overuse antibiotics,” Hallundbæk Mikkelsen says.