It's common for people to have high blood sugar for years and not know it. Although many people function quite well for a time with untreated diabetes, eventually the disease causes complications. Unfortunately, once these occur, it's often difficult or impossible to undo the damage. Some of the complications of chronic high blood sugar are eye disease, circulatory problems, kidney disease, and nerve problems. Untreated eye disease can lead to blindness.
Cardiovascular disease can lead to heart attacks and stroke, often at an early age.
Nerve problems can lead to numbness or even pain in the legs and feet, and impotence in men. Type 2 diabetes is a treatable condition. It's possible for many people to control it with diet and exercise alone. In fact, achieving and maintaining a normal weight can often be enough to keep the blood sugar normal, eliminating symptoms and essentially curing the disease. Some people may need to use oral medications or insulin.