Concerning new research suggests repeated antibiotic use could raise the risk of type 2 diabetes by altering gut bacteria.

The findings highlight the need to reduce the prescription of unnecessary antibiotics, the Society for Endocrinology reported.

A team of researchers from the Departments of Gastroenterology and Medical Oncology at the University of Pennsylvania looked at over cases 200,000 antibiotic prescriptions given to diabetics at least one year before their diagnosis, and compared them to 800,000 prescriptions given to non-diabetics.

The findings revealed patients prescribed at least two courses of penicillins, cephalosporines, quinolones and macrolides had a significantly higher risk of developing type 2 diabetes. The findings suggest patients who are prescribed two to five courses of penicillin have an 8 percent higher risk of developing type 2 diabetes, those who are prescribed over five penicillin courses have as much as a 23 percent higher risk of developing the condition. Two to five courses of quinolones appeared to up type 2 diabetes risk by 15 percent, and five or more courses raised risk by a whopping 37 percent.

"Gut bacteria have been suggested to influence the mechanisms behind obesity, insulin resistance and diabetes in both animal and human models," said lead author of the study Ben Boursi. "Previous studies have shown that antibiotics can alter the digestive ecosystem."

The researchers noted the study did not show a concrete cause and effect link, but suggests gut bacteria diversity is responsible for the correlation between antibiotic use and type 2 diabetes. There was no observed risk increase associated with anti-virals or anti-fungal medications.

"Over-prescription of antibiotics is already a problem around the world as bacteria become increasingly resistant to their effects" Boursi said. "Our findings are important, not only for understanding how diabetes may develop, but as a warning to reduce unnecessary antibiotic treatments that might do more harm than good."

The findings were published in a recent edition of the European Journal of Endocrinology.