The number of American adults treated for diabetes jumped from about 9 million in 1996 to 19 million in 2007, according to a report issued in January by the Agency for Healthcare Research and Quality. The largest increase was among adults aged 45 to 64. The number of patients with diabetes in that age group climbed from 3.6 million to 8.9 million. Among adults 65 and older, the number of diabetes patients nearly doubled from 4.3 million to 8 million in that time. Researchers say the most obvious culprit is the huge increase in adults who are overweight and obese, but that some of the higher numbers are the result of greater testing and at younger ages.