Nancy A. Melville
September 12, 2019
Amid concerns about the global diabetes epidemic, a new systematic review shows surprising stability, and even reductions in some countries, when looking specifically at the incidence — or new cases — of diabetes over recent years.
The results "suggest that trends in the diabetes epidemic in some high-income countries have turned in a more encouraging direction compared with previous decades," write the authors, led by Dianna Magliano, PhD, MPH, at the Baker Heart and Diabetes Institute in Melbourne, Australia, in their article published this week in BMJ.
Rather than the trends of new cases, studies more commonly report on prevalence rates — or the overall proportion of cases in a population — which can, in fact, represent a "crude and misleading metric of a trajectory of an epidemic," because increases in prevalence can represent factors such as improved survival as well as new diagnoses, say Magliano and colleagues.
But in an accompanying editorial, Louise McCombie, BSc, at the University of Glasgow, UK, and colleagues urge caution when interpreting the findings.
"Incidence is harder to measure (than prevalence) and more likely to have errors," Mike Lean, MD, coauthor of the editorial and a professor of human nutrition at the School of Medicine, GRI Campus College of Medical, Veterinary and Life Sciences, University of Glasgow, told Medscape Medical News.
And he said he finds it hard to believe that new cases of diabetes are falling when obesity is on the rise almost everywhere in the world.
"While we all long for signs that diabetes is in retreat, this sensibly optimistic systematic review does not provide definitive evidence that true incidence is finally falling," he and his fellow editorialists conclude.
Decline in Incidence of Diabetes in Some Places in 2004-2016
For the review, the authors identified 47 studies in 121 populations that met the inclusion criteria of reporting on diabetes incidence in adults in two or more time periods.
Although many of the studies did not accurately specify the type of diabetes, the results apply predominantly to type 2 diabetes because of the greater incidence than type 1 diabetes, the authors note.
Looking at the period of 1960-1989, the incidence of diabetes increased in 36% of the populations, while rates were stable in 55% and diabetes incidence decreased in 9%.
In 1990-2005, the incidence of diabetes increased in 66% of populations, while rates were stable in 32% and decreased in just 2%.
However, in the most recent time period, 2006-2014, there was a notable shift.
"We show evidence that the incidence of diagnosed diabetes increased in most populations from the 1960s to the early 2000s, after which a pattern emerged of leveling trends in 30% and declining trends in 36% of the reported populations," the authors write.
Stable or decreasing diabetes trends were largely seen in Europe and East Asia.
Stepped Up Prevention Efforts? But New Cases Likely in Many Regions
Preventive strategies and public health education and awareness campaigns in some places "could have contributed to this flattening of incidence rates, suggesting that...efforts to curb the diabetes epidemic over the past decade might have been effective," the researchers say.
In the United States, for instance, some research shows improved diets, such as reduced sugar consumption and other behaviors in recent years, and similar reductions have been reported in Norway and Australia, while fast food intake has decreased in Korea.
But Magliano and colleagues admit that a key limitation of their review is the lack of data for non-European populations, including low- and middle-income countries, with incidence data lacking for key regions including the Pacific Islands, Middle East, and South Asia.
"Large increases in incidence could still be occurring in these areas," the authors concede.
Hard to Believe Cases of Diabetes Falling When Obesity Is Increasing
In his comments to Medscape Medical News, Lean expanded upon some of the difficulties he sees in interpreting the study.
"Some of the data they used were actually not incidence. Instead of date of diagnosis they used date when a drug was first started," for example, he said.
"That can vary from immediately at diagnosis to anything up to 5 years or more, and some patients with diabetes are never prescribed a drug at all. Indeed they don't need drugs if they manage to lose plenty of weight," Lean noted.
And that leads to the key piece of the puzzle that needs to be moved for meaningful change, he stressed.
"Type 2 diabetes is virtually entirely driven by overweight and obesity. There has been no decline in overweight or obesity, so being an old-fashioned experienced doctor, trained in research methods, I don't believe there can have been a real decline in incidence of type 2 diabetes," he said.
Funding for the study was received from the Centers for Disease Control and Prevention. The authors have reported no relevant financial relationships. Lean is conducting research on a drug for obesity funded by Novo Nordisk and has given paid advice to Roche on obesity.