More Americans are diagnosed with diabetes than ever before, though improved preventive care has cut the rate of serious complications such as heart attack and stroke over the past 20 years, a government report found.

While the rate of medical complications fell, the number of Americans diagnosed with the disease tripled to 20.7 million in 2010 from 6.5 million in 1990, according to research from the Centers for Disease Control and Prevention published this week in the New England Journal of Medicine. The jump in diagnoses resulted in more people suffering from complications despite the rate reduction, said Linda Geiss, one of the study authors.

"Although we've seen a decline in the rates and we've come a long way in preventing the complications and improving the quality of life for people with diabetes, most of the numbers are still increasing," Geiss, head of diabetes surveillance at the CDC in Atlanta, said in a telephone interview. "We need to make some progress in preventing Type 2 diabetes in order to help decrease these numbers."

Diabetes, which is caused when the body doesn't use insulin properly or doesn't make the hormone, is the seventh-leading cause of death in the U.S. Insulin is a hormone secreted by the pancreas that helps the body control blood sugar. Type 2 accounts for 90 percent to 95 percent of U.S. cases.

About 79 million Americans are at risk for developing diabetes, according to the CDC. Diabetes and the associated complications cost $176 billion in medical expenses each year.

Diabetes drug sales may surpass $50 billion by 2017, according to data compiled by Bloomberg. The newest therapy, GlaxoSmithKline's Tanzeum, won U.S. approval Tuesday to control Type 2 diabetes. Analysts estimate the treatment will generate $306.6 million in 2017.

The report issued this week found the rate of heart attack among diabetics declined 68 percent from 1990 to 2010, while stroke fell 53 percent and amputations were cut 51 percent. Rates of deaths from high blood sugar and end-stage kidney failure also fell during the 20 years. The largest decline in many of the complications was seen in those ages 75 and older.

The CDC has said that 25.8 million Americans have diabetes, including 7 million who haven't been diagnosed.