Type 1 Diabetes Incidence in Sweden Far Higher Than Believed

Miriam E. Tucker

April 09, 2014

The incidence of type 1 diabetes among 0- to 34-year-olds in Sweden is 2 to 3 times higher than previously thought, a new analysis of multiple nationwide registries found.

The results were published online April 6 in Diabetologia by Araz Rawshani, MD, from the Swedish National Diabetes Register and Institute of Medicine, the Sahlgrenska Academy, University of Gothenburg, Sweden.

International multicenter studies beginning in the 1980s have reported annual increases in type 1 diabetes of about 3% per year among children aged 14 years and younger, with the steepest increases among those aged 0 to 4 years. However, data have been conflicting as to whether there has been a corresponding increase among older teens and young adults or whether the overall incidence has stayed the same and merely shifted to a younger age of onset.

Using 2 methods to estimate the incidence of type 1 diabetes among Swedish residents aged 0 to 34 years, Dr. Rawshani and colleagues found type 1 diabetes is occurring as often among adolescents and young adults aged 15 to 34 as it is among 0- to 4-year-olds.

"We certainly did not expect that incidence rates would be so high….These patients need attention," he told Medscape Medical News.

"Previous research has led to the belief that the incidence among adolescents and young adults is decreasing," Dr. Rawshani continued. "This might have led to neglect of these patients in several ways, such as lower suspicion of type 1 diabetes in patients presenting with such symptoms….This patient group is atypical, because we consider type 1 diabetes as a disease of childhood. Therefore, these patients are at risk of falling through the cracks."

The reason for the increase remains elusive, with the prevailing theory being that it can't simply be a matter of genes, which don't evolve that quickly, and must be something in the environment. "Many more efforts are needed to solve the conundrum of autoimmune diabetes. We still don't know what triggers the autoimmune destruction of pancreatic beta-cells. Parallel progress in epidemiology and basic science will hopefully solve the puzzle," he said.

Capture-Recapture Ups Estimates

Dr. Rawshani and colleagues analyzed data from 3 nationwide registers: the National Diabetes Register (NDR), which covers patients aged 18 years and older; the Diabetes Incidence Study in Sweden (DISS), which includes incident cases of diabetes, distinguishing by type, among Swedes aged 15 to 34 years; and the Swedish Childhood Diabetes Register (SCDR), which includes patients aged 14 and younger.

They also used data from the prescription drug register (PDR) of the National Board of Health and Welfare as a proxy for type 1 diabetes in those aged 0 to 34 years by limiting the analysis to patients who had been prescribed insulin only and never any other glucose-lowering drugs. For females, they required at least 3 prescriptions of insulin to exclude those with gestational diabetes.

The investigators used a "capture-recapture" method by which the number of patients in each source/register and the number common in the sources/registers are used to estimate the true population size.

For patients aged 14 years and younger, the incidence rates from the PDR were very similar to those reported in the SCDR in 2005–2007. They range from 20.0 per 100,000 person years among 0- to 4-year-olds in 2008 to 57.2 per 100,000 person-years for 10- to 14-year-olds in 2009.

However, for the 15–19 age group, incidence rates were 2 to 3 times higher in the PDR than in the DISS, ranging from 11.1 to 15.9 per 100,000 person-years during 2007–2009 in the DISS to 31.8 to 36.6 per 100,000 person-years in the PDR.

For ages 20 to 34, the DISS had the lowest incidence and the PDR the highest for the years 2007–2009, but the capture-recapture method produced the highest rates of all. For example, the incidence rate in the PDR for 20- to 24-year-olds in 2009 was 26.5 per 100,000 person-years, while the capture-recapture estimate was 31.2 per 100,000 person-years.

Policy and Research Implications

Dr. Rawshani told Medscape Medical News, "Policy makers should be aware that the incidence of type 1 diabetes in adolescents and young adults is 2 to 3 times higher than previously believed, and resources to manage these patients should be allocated to healthcare system. Policy makers should also support research in epidemiology and basic science in this field."

Obtaining precise disease estimates requires registry data that aren't available in most places, he told Medscape Medical News.

"We believe that to estimate the true population size on a nationwide scale, the optimal method is to use a source that inevitably registers all patients immediately at the time of diagnosis, like the PDR in Sweden."

The study was funded by the National Diabetes Register in Sweden. The authors have reported no relevant financial relationships.

Diabetologia. Published online April 6, 2014. Article

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