New cases of diabetes among U.S. adults are decreasing even while obesity rates are rising, a trend that has health officials puzzled.
Federal data released today in the journal BMJ Open Diabetes Research & Care shows that the number of new cases of diabetes was 1.3 million in 2017 (6 new cases per 1,000 adults), compared to 1.7 million in 2009 (9.2 new cases per 1,000 adults). According to the Centers for Disease Control and Prevention (CDC), this 35% drop represents “the longest decline since the government started tracking the statistic nearly 40 years ago.”
Certain factors may partially explain the drop in new diagnoses: In the late 1990s, the blood sugar threshold for a diabetes diagnosis was lowered, which likely led to an increase in the number of previously unrecognized cases from 2000–2010. “We might have mined out a lot of the previously unrecognized cases,” notes John Buse, MD, PhD.
Another possibility is that doctors have increasing been using the HbA1c test (a measure of glucose control over the previous 2–3 months) to diagnose diabetes. This test is more convenient than others used for diagnosis, as it does not require fasting or multiple blood draws, but it may miss a large number of early, symptomless cases, according to some experts.
A third potential explanation is that more health-care providers have been officially diagnosing prediabetes, in which blood glucose levels are high, but not high enough to be classified as diabetes. Receiving this diagnosis may be motivating increasing numbers of patients to adopt lifestyle changes such as improved diet and increased physical activity, helping them avoid a diabetes diagnosis.
According to lead report author Stephen Benoit, MD, of the CDC, “The bottom line is we don’t know for sure what’s driving these trends.”