Diabetes mellitus is a common disease that interferes with the body's ability to store energy from food. The pancreas makes a substance called insulin that helps to store energy from food. Type 1 diabetes (juvenile diabetes) occurs when the pancreas stops making insulin. In type 2 diabetes (adult-onset diabetes), the body makes plenty of insulin but is unable to use it normally. In both cases, the result is high blood sugar levels. Over time, high blood sugar levels can lead to blindness, kidney failure, nerve damage, and heart disease. Fortunately, good care with diet, exercise, and medications can prevent the development of complications. Good care includes treatment to keep blood sugar levels normal. People with diabetes have more heart attacks and strokes than people without diabetes. Controlling blood pressure and cholesterol helps to prevent these complications. For people with diabetes who also have high blood pressure and cholesterol problems, good care also includes intensive treatment of these conditions. Type 1 diabetes usually does not go long before being diagnosed. However, many people with type 2 diabetes have diabetes for years before symptoms begin. Testing people who have no symptoms to try to detect disease early is called screening. Screening for diabetes would be helpful only if people who begin treatment before symptoms develop do better than people who start treatment after symptoms develop.