Medical Encyclopaedia › Diabetes mellitus (short definition)
In brief: Diabetes mellitus is a chronic metabolic disease in which blood sugar is permanently raised because the body produces too little insulin or insulin does not work sufficiently. More than eight million people in Germany live with diabetes, the vast majority with type 2 diabetes.
Types
In type 1 diabetes, the immune system destroys the insulin-producing cells of the pancreas; those affected need insulin from the start. Type 2 diabetes develops over years from insulin resistance, favoured by predisposition, overweight and lack of exercise. There is also gestational diabetes and rarer forms, for example due to diseases of the pancreas or genetic causes.
Symptoms
Typical signs of high blood sugar are severe thirst, frequent urination, tiredness, weight loss, poorly healing wounds and frequent infections. Type 2 diabetes often causes no symptoms at first and is therefore frequently discovered by chance. In type 1 diabetes, symptoms can set in rapidly and lead to life-threatening ketoacidosis.
Diagnosis
The diagnosis is based on fasting blood sugar, a random blood sugar, the oral glucose tolerance test or the HbA1c value, which reflects the average blood sugar over the last two to three months. An HbA1c of 6.5 per cent or more is considered diagnostic; values between 5.7 and 6.4 per cent indicate prediabetes.
Complications
Permanently raised blood sugar damages large and small blood vessels as well as nerves. Possible consequences are heart attack, stroke, kidney damage, retinal damage, nerve damage and diabetic foot syndrome. Regular checks of the eyes, kidneys and feet help to detect damage early.
Treatment
In type 2 diabetes, diet, exercise and weight loss if needed come first. The first medicine is often metformin; in heart or kidney disease, SGLT2 inhibitors or GLP-1 receptor agonists are added, which can also protect the heart and kidneys. If this is not enough, insulin is added. In type 1 diabetes, insulin is indispensable, today often with an insulin pump and continuous glucose monitoring. Education programmes are an integral part of treatment.
When to see a doctor?
In the case of typical symptoms, a family history or overweight, a blood sugar check is advisable; in Germany it is part of the health check-up from the age of 35. Severe nausea, vomiting, abdominal pain, deep breathing or impaired consciousness in a person with diabetes require immediate medical help.
Related terms in the encyclopaedia
Type 1 diabetes, Type 2 diabetes, Insulin, Insulin resistance, HbA1c, Prediabetes, Metformin, SGLT2 inhibitors, GLP-1 receptor agonist, Diabetic foot
Sources
- Bundesärztekammer, KBV, AWMF: Nationale VersorgungsLeitlinie Typ-2-Diabetes, leitlinien.de
- Deutsche Diabetes Gesellschaft (DDG): S3-Leitlinie Therapie des Typ-1-Diabetes
- Robert Koch-Institut: Diabetes-Surveillance, diabsurv.rki.de
- IQWiG: gesundheitsinformation.de – Gesundheitsinformationen des Instituts für Qualität und Wirtschaftlichkeit im Gesundheitswesen
Note: This article is for general information and does not replace advice, diagnosis or treatment from a doctor or pharmacist. Last updated: October 2026.