Taking antibiotics seems to be associated with an increased risk of developing type 2 diabetes, according to the Journal of Clinical Endocrinology & Metabolism.

Researchers from Denmark matched 170,504 people with type 2 diabetes and 1,364,008 controls, with a median age of 62 years. About half (52.3 per cent) were males.

Type 2 diabetes patients filled, on average, 0.8 antibiotic prescriptions a year, compared with 0.5 prescriptions among controls. People who took at least five courses of antibiotics between January 1, 1995 and July 1, 2012 were 53 per cent more likely to develop type 2 diabetes than those who took 0-1 prescriptions.

“A clear dose-response effect” emerged: two to four courses increased the risk of type 2 diabetes by 21 per cent.

The increased type 2 diabetes risk was especially marked with narrow-spectrum and bactericidal antibiotics (55 and 48 per cent increases respectively) compared to broad-spectrum and bacteriostatic antibiotics (31 and 39 per cent respectively). The increased use of antibiotics among people who developed type 2 diabetes emerged up to 15 years before diagnosis.

Use of antibiotics was 20 per cent higher in the type 2 diabetes group 15 years before diagnosis, increasing to 35 per cent the year before. Use was also higher following diagnosis.

“Although we cannot infer causality from this study, the findings raise the possibility that antibiotics could raise the risk of type 2 diabetes. Another equally compelling explanation may be that people develop type 2 diabetes over the course of years and face a greater risk of infection during that time,” says study author, Kristian Hallundbæk Mikkelsen, Gentofte Hospital, Hellerup.

Antibiotics can change the composition of gut bacteria, and certain gut bacteria may contribute to the impaired ability to metabolise sugar seen among people with diabetes.

“Further investigation into the long-term effect of antibiotic use on sugar metabolism and gut bacteria composition could reveal valuable answers about how to address this public health crisis,” Dr Mikkelsen comments. “Patterns in antibiotic use may offer an opportunity to prevent the development of the disease or to diagnose it early.” (doi:10.1210/jc.2015-2696)