A 40 percent decline in the death rate of diabetic American adults from heart disease and strokes is a sign that patients are taking better care of themselves and receiving improved treatment, according to a government study released on Tuesday. Overall death rates among diabetic adults dropped 23 percent from 1997 to 2006, according to the study by researchers at the U.S. Centers for Disease Control and Prevention and the National Institutes of Health. The study examined data from 250,000 patients. Despite the significant decline in diabetic deaths from cardiovascular disease, the rate is still twice as high as those without the disease, the CDC said.