Type 2 diabetes mellitus is a common disease that interferes with the body's ability to store energy. The pancreas makes a substance called insulin, which helps the body store energy from food. In type 2 diabetes (adult-onset diabetes), the body makes plenty of insulin but cannot use it normally. The result is high levels of blood sugar, which can eventually lead to blindness, kidney failure, nerve damage, and heart disease. Fortunately, good care with diet, exercise, and medications can prevent complications. Persons who are overweight, have a family history of diabetes, are older, or had diabetes during pregnancy are at higher risk for type 2 diabetes than persons without these risk factors. Smokers also have a higher risk for type 2 diabetes than nonsmokers, but the cause of this relationship is not well understood. It is also not known whether quitting smoking decreases a person's risk for diabetes. Quitting smoking decreases inflammation in the body, and inflammation may have something to do with the development of diabetes. However, quitting smoking sometimes causes weight gain, and weight gain could increase the risk for diabetes.