Taking too many antibiotics could raise the risk of Type 2 diabetes, research has shown.

A study of more than a million people, including 170,500 with the disease, found a clear link between higher numbers of prescriptions for the drugs and having a diabetes diagnosis.

Increasing amounts of antibiotics led to a greater chance of developing the disease.

Antibiotics may affect the “microbiota” of bugs in the gut, some of which are known to influence metabolism. But an alternative explanation could be that people with as-yet undiagnosed diabetes may be more prone to infection, and therefore use more antibiotics, say the scientists.

The researchers, whose findings appear in the Journal of Clinical Endocrinology & Metabolism, tracked antibiotic prescriptions made out for 170,404 Danes with Type 2 diabetes and 1.3 million people who did not have the disease.

Five or more prescriptions over a period of up to 15 years was associated with a 53 per cent increase in risk compared with being given antibiotics just once, or never.

The relative risk was slightly higher for antibiotics effective against a narrow range of bacteria as opposed to broad-spectrum drugs.

Study author Kristian Mikkelsen, from Gentofte Hospital in Hellerup, Denmark, said: “In our research, we found people who have Type 2 diabetes used significantly more antibiotics up to 15 years prior to diagnosis compared to healthy controls.

“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.”

Type 2 diabetes is one of the greatest health problems facing the UK and other countries in the Western world.

More than three million people in the UK are believed to be living with the disease. The number of British diabetics has more than doubled since 1996 and experts predict that by 2025 it could reach five million.

The study found that people with Type 2 diabetes filled out 0.8 prescriptions for antibiotics per year on average. In comparison, non-diabetic individuals filled out 0.5 prescriptions per year.

Previous research has shown that antibiotics can alter the kind of bacteria living in the gut. Some of these bugs may contribute to the impaired ability of people with diabetes to metabolise sugar.

Mikkelsen added: “Diabetes is one of the greatest challenges facing modern health care, with a globally increasing incidence.

“Further investigation into 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.

“Patterns in antibiotic use may offer an opportunity to prevent the development of the disease or to diagnose it early.”

Commenting on the research, microbiologist Professor Mark Wilcox, from Leeds General Infirmary, said: “The study data are interesting and are certainly provocative. It is plausible that the detrimental effects of antibiotics on the bacteria present in our gut, which actually outnumber our human cells, can lead to diseases that are due to malfunctioning of body control mechanisms.”

Jodie Lindsay, professor of Microbial Pathogenesis, at St George’s, University of London, said: “Considering the enormous burden that diabetes has on our healthcare systems, it is important that further research is funded to investigate the role of antibiotics on the risk of developing diabetes.”

Richard Elliott, from Diabetes UK, stressed that the research did not demonstrate a causal link between antibiotics and Type 2 diabetes.

He said: “The influence of other key diabetes risk factors could not be ruled out and it might be that obesity and Type 2 diabetes cause an increased use of antibiotics, because both are thought to increase the risk of infection.

“As the researchers themselves suggest, clinical trials are needed to work out the causes involved. We know that being overweight is the key risk factor for Type 2 diabetes, and that the best way to prevent the condition is to maintain a healthy weight by eating a healthy balanced diet and by taking regular physical activity.”