The findings of a recent Danish study of antibiotics and diabetes strengthens the growing body of evidence that links the two. The reason why people who take more antibiotics are more likely to develop diabetes remains unknown, however.

Dr. Kristian Hallundbæk Mikkelsen led the study of more than a million residents of Denmark that compared their antibiotic use and diabetes. She is affiliated with the Center for Diabetes Research at Copenhagen University’s Hospital Gentofte.

Mikkelsen and her research team analyzed data from various sources:

  • Danish National Registry of Patients
  • Danish National Prescription Registry
  • Danish Person Registry

The researchers tallied antibiotic prescriptions filled between 1995 and 2012 for adult men and women. Of these individuals,

  • 170,000 were diagnosed with type 2 diabetes
  • Approximately 1.3 million were never diagnosed as diabetic but matched the diabetic study group in age, gender, and other socioeconomic demographics

Some findings of the study include:

  • People who took five or more antibiotic prescriptions were more likely to become diabetic than those who took no more than one prescription.
  • Diabetes risk increased as more antibiotic prescriptions were filled.
  • Increased risk was associated with diabetes diagnosis even 15 years after antibiotic use.
  • After diagnosis, diabetics continued to take more antibiotics than those without disease.

Antibiotic use did not significantly vary diabetes risk according to antibiotic type or to the medical condition which prompted the prescription although slight differences were observed. Narrow-spectrum and bactericidal antibiotics were associated with a slightly higher risk of type 2 diabetes than broad-spectrum and bacteriostatic antibiotics:

  • Narrow-spectrum antibiotics target specific types of bacteria.
  • Broad-spectrum antibiotics target a less clearly defined array of bacteria.
  • Bactericidal antibiotics kill all bacteria they come in contact with.
  • Bacteriostatic antibiotics make it impossible for bacteria to reproduce, eventually killing off a colony by preventing population growth or reducing the colony to harmless size.

It is unknown at this time if antibiotics alter body chemistry in ways that trigger diabetes development or if the earliest stages of diabetes, when it is still undetectable, make an individual more prone to infection. Diabetics are more prone to infection than the general population without the disease.

The study of the microbiome (also referred to as microbiota, gut bacteria, and gut flora) in recent years has linked this environment of gastrointestinal microorganisms to the immune system and to various diseases, including diabetes and obesity. Mikkelsen cited animal research that revealed gut bacteria necessary for sugar and fat metabolism change when exposed to antibiotics. She suggests use of antibiotics may similarly impair the human body’s ability to metabolize sugar and fat enough to trigger the onset of type 2 diabetes.


  1. Mikkelsen, Kristian Hallundbæk, et al. "Use of Antibiotics and Risk of Type 2 Diabetes: A Population-Based Case-Control Study." JCEM / The Journal of Clinical Endocrinology & Metabolism (2015). Web. 11 Sept. 2015.
  2. "Get Smart: Know When Antibiotics Work." CDC / Centers for Disease Control and Prevention. US Department of Human Health and Services, 17 Apr. 2015. Web. 11 Sept. 2015.