It depends on what kind of diabetes you are inquiring about.
- Type 1 diabetes is non-preventable and non-curable. It is an autoimmune disease, the pancreas has cells called beta cells that create the hormone insulin and insulin controls the glucose/blood sugar levels in the body. With type 1 the pancreas no longer functions at all. It comes from your genes, so if someone in your family has type 1 or any kind of diabetes, you are at a higher risk. Type 1 requires daily insulin shots, done at home, by yourself.
- Type 2 - The pancreas may still work a little, but doesn't provide enough insulin to keep the blood sugar under control. Most type 2 patients take oral insulin, but in extreme cases they must take the shots. Type 2 can be prevented; it is widely caused by being overweight and/or not exercising enough. So stay fit.
- Gestational - high blood sugar caused by pregnancy, leading to a temporary diabetes. Requires treatment during pregnancy, usually resolves itself after the child is born, but both mother and child are at higher risk for type-2 diabetes afterwards. Go to diabetes.org that's the American Diabetes Association website.
- Pre-diabetes - the final one, not considered to be a type, but it's the beginning to diabetes, can lead to type 1 or 2. It's just where the pancreas works almost right, but not completely, leading to slightly higher blood sugar levels. Normally this is caused by genes also.
- Pancreatitis - chronic inflammation of the pancreas, can cause permanent damage to the pancreas that can lead to type-1 diabetes. So you can be maybe 50+ and then get type 1.
Diabetes has a long list of complications. I'll list a few complications here. Blindness, Amputations, Kidney failure, Peripheral Arterial Disease, known as PAD for short, and Heart Attacks & Strokes.
One of the least-discussed complications of diabetes (all types) is diabetic deterioration: damage to the pancreas and body from high blood glucose (hyperglycemia), which in turn reduces the effectiveness of the pancreas at making insulin, and increases insulin resistance. These in turn make diabetes worse, causing poorly-treated type-2 diabetics over time to become more and more like type-1 patients. For this reason, it's best to treat high blood glucose aggressively even in early stages, so as to prevent the later stages. See the link below "Keeping your blood sugar under control"