There are two main types of diabetes: type 1 and 2.
The trigger for type 1 diabetes is a congenital autoimmune disease, ie a defect of the immune system. Type 1 diabetes usually develops during childhood and is often referred to as juvenile diabetes. Type 2 diabetes is much more common and is also called age-related diabetes. The cause of type 2 diabetes is an increasing insulin resistance of cells with age: sugar can no longer be adequately absorbed by cells from the blood.
The genes of a person determine to a large extent whether you suffer from type 2 diabetes. The risk increases with age, but is also increased by obesity, unhealthy diet and lack of physical activity. This is why young people are increasingly being affected by type 2 diabetes. The positive side: a balanced diet and sufficient physical activity can counter type 2 diabetes.