Diabetes is widely misunderstood as a mild, manageable disease. In fact, the metabolic disorder is a deadly and costly disease that is rapidly increasing in the United States and around the world. At least 16 million Americans have the disease, caused by a lack or shortage of insulin. The incidence of diabetes in the U.S. has increased by 41 percent over the past decade. Experts say diabetes is partly genetic and at least partly behavioral. Obesity and lack of exercise are key risk factors for the most common form. Public health officials are spreading the word about the epidemic, while doctors and scientists are trying to develop better ways of treating it, and someday a way of preventing it.