New research published in Diabetologia (the journal of the European Association for the Study of Diabetes) suggests that Sweden--the country already thought to have the second highest prevalence of type 1 diabetes in the world--could have 2-3 times more adolescents and young adults with type 1 diabetes than previously estimated. The research is by Dr Araz Rawshani, Swedish National Diabetes Register, Gothenburg, Sweden, and colleagues.
Current estimates in Sweden are based on the Diabetes Incidence Study in Sweden (DISS), which has been around since 1983. The DISS is one of very few registers to record data on adolescents and young adults and therefore findings from the DISS study have had implications for diabetes research and care in many countries. Dr Rawshani and colleagues found that the DISS had very low coverage which discards previous findings.
The researchers found that they could more accurately estimate actual numbers by examining the country's Prescribed Drug Register (PDR) and establishing a diagnosis of type 1 diabetes via a patient's prescription medications; men with at least 1 and women with at least 3 prescriptions for insulin were included as having type 1 diabetes if they had not been given oral antidiabetic drugs. Women needed three prescriptions to avoid confusion with gestational diabetes, and oral antidiabetic drugs ruled out a type 1 diabetes diagnosis since these are used in patients with type 2 diabetes.
They then compared the results from the PDR with incidence rates in patients aged 14 and younger in the Swedish Childhood Diabetes Register (SCDR), which has almost all (95-99%) cases in that age group included, and by assessing diabetes type among 18-34 year olds in the National Diabetes Register (NDR). The absolute number of cases in adolescents and young adults aged 18-34 years was found to be 1,217 in the PDR, almost 3 times that originally thought (435 based on the DISS).
The researchers also found that their findings did not back previous research that the incidence is increasing among children and therefore decreasing in the rest of the population. Previous theories have stated that individuals develop disease earlier, but the total number of individuals has not changed. The new study shows that the incidence in adolescents and young adults is 2-3 times higher than previously reported and is actually as high as that reported in children aged 0-4 years. Consequently these previous theories are now being strongly questioned. "Our analysis of the Prescribed Drug Register found that that incidence rates in young people aged 15-34 years were equal to those in children aged 0-4 years," say the authors.
Since all patients with a diagnosis of type 1 diabetes must be entered into the PDR, the researchers say that this should be the ongoing method to determine type 1 diabetes incidence in any future studies. The authors say: "The incidence of type 1 diabetes is 2 times as high in 15 year olds. We believe that the Prescribed Drug Register is likely to be the gold standard for monitoring the incidence of type 1 diabetes, particularly in patients age 30 and younger. This method is feasible, reliable and cost-effective."
In terms of estimates in other countries, the authors note that "few countries can make similar estimations due to lack of possibilities to link different registries. Sweden has unique abilities in this area, due to the unique personal identification number which is assigned to every Swede and available in all health registers." But the authors add "we believe our findings are presumably applicable to other high-income countries due to the similarities in populations, lifestyle and incidence patterns."
The authors point out that type 1 diabetes was once a rare disease. They say: "It is not known why the incidence began to increase drastically in the 1980s. It is predicted that the incidence in Europe will rise by an alarming 70% between 2005 and 2020. The present study shows that the incidence in adolescents and young adults is 2-3 times higher than previously thought. Importantly, all epidemiological data suggest strongly that the changes in disease prevalence is due to changes in our environment, which now cause more individuals to develop disease. We now have a simple method to monitor the disease on a nationwide scale but many more multinational efforts are needed to resolve the conundrum of type 1 diabetes."