Diabetes is caused by an inability to produce enough insulin or use insulin effectively within the body. Insulin allows blood sugar (glucose) to enter cells where it can be used for energy. When the body lacks insulin or is unable to effectively use it, blood sugar rises and can have serious health consequences. High blood sugar can lead to heart disease, stroke, blindness, kidney failure, and other complications. 
Type 1 diabetes is an autoimmune disease, and accounts for about 5 to 10 percent of all diabetes cases. People with type 1 diabetes must take insulin throughout their lives to survive. Type 2 diabetes, also called adult-onset diabetes, accounts for roughly 90 to 95% of all cases. Unlike with type 1, there are a variety of measures that can help prevent the onset of type 2 diabetes. They include such lifestyle changes as exercising and maintaining a healthy diet.