New cases of diabetes in the United States decrease as obesity increases

The number of new cases of diabetes in American adults is steadily decreasing, even as the rate of obesity increases, and health officials do not know why.

New federal data released on Tuesday indicates that the number of new diabetes diagnoses dropped to about 1.3 million in 2017 from 1.7 million in 2009.

Previous research has shown a decline and the new report indicates that this has been going on for almost a decade. But health officials are not celebrating.

"In the end, we do not know for sure what motivates these trends," said Dr. Stephen Benoit, lead author of the new report, Centers for Disease Control and Prevention. Among the possibilities: Modify tests and get people to improve their health before becoming diabetic.

The report was published by the journal BMJ Open Diabetes Research & Care. Statistics cover until 2017. Last year's figures are not yet available, Benoit said.

Diabetes is a disease in which sugar accumulates in the blood. The most common form is related to obesity and the number of diabetics has increased as obesity rates in the United States increase.

But other factors may also have pushed up the annual diagnoses of diabetes from 2000 to 2010, and they could partly explain why the numbers have declined since then, some experts said.

First, the diagnostic threshold was lowered in the late 1990s. This has led to more people being considered diabetic, but the impact of this may have played out.

"We may have eliminated a large number of previously unrecognized cases" and new diagnoses in recent years are therefore likely to be new diseases, said Dr. John Buse, diabetes expert at the University of Carolina North.

Meanwhile, doctors are increasingly using a new blood test to diagnose diabetes. This is much easier than tests that require patients to fast for 12 hours or to undergo repeated blood tests for more than two hours.

The American Diabetes Association has recommended the new test, known as the hemoglobin A1C blood test, for routine screening in 2010. Since it is easier to perform, it should lead to more diagnoses. But some experts say it could miss a lot of the first cases in which people do not show symptoms. "You may have forgotten people who would have been diagnosed" with older tests, Benoit said.

Another possibility: more and more doctors are diagnosing a "prediabetes", a health problem characterized by high blood sugar, but insufficient to reach the threshold of diabetes. Doctors usually push these patients into exercise programs and incite them to change diets.

"Prediabetes is becoming an increasingly accepted diagnosis" and could lead an increasing number of patients to improve their health before becoming diabetic, said Dr. Tannaz Moin, an expert at UCLA.

The new report is based on a large national survey conducted annually by the government. Participants were asked if they had been diagnosed with diabetes and whether the diagnosis had been made the previous year.

It revealed that the rate of new cases of diabetes fell to 6 per 1,000 US adults in 2017, from 9.2 per 1,000 in 2009. This is a 35% drop and represents the longest decline since that the government started tracking statistics almost 40 years ago, according to the CDC.

The decrease was mainly observed in white adults, the researchers said.

Meanwhile, the overall estimate of the number of Americans with diabetes – whether recent diagnosis or not – has remained stable at 80 per 1,000 US adults. This translates to about 21 million Americans.