The number of new diabetes cases fell from 1.7 million in 2009 to 1.3 million in 2017, according to federal data released Tuesday, the Associated Press reported.
"The bottom line is we don't know for sure what's driving these trends," said Dr. Stephen Benoit, Centers for Disease Control and Prevention, the lead author of the report in the journal BMJ Open Diabetes Research & Care.
Possible reasons include changes in testing and getting people to make healthy lifestyle changes before they develop diabetes, the AP reported.
The data show that the rate of new diabetes cases fell from 9.2 per 1,000 in 2009 to 6 per 1,000 U.S. adults in 2017, a 35% drop. That's longest decline since the government started tracking the data nearly 40 years ago, according to the CDC.
The decrease mainly occurred among white adults. Diabetes has continued to rise among young adults and blacks and Hispanics, the AP reported.
And despite the decline in the number of new cases, the number of Americans with diabetes has been stable at 80 per 1,000 adults, or about 21 million.