Trends in the incidence of young-adult-onset diabetes by diabetes type: a multi-national population-based study from an international diabetes consortium

Background Population-based incidence data on young-onset type 1 (T1DM) and type 2 diabetes (T2DM) are lacking. We examined secular trends in the incidence of diagnosed T1DM and T2DM with an age of onset between 15 and 349 years.

Methods We assembled eight administrative datasets from high-income jurisdictions describing incidence by diabetes type. We modelled T1DM and T2DM incidence rates using Poisson regression including age and calendar time (2000–2020) by sex.

Findings There were 349591 incident diabetes cases from 346 million person-years of follow-up among people aged 15–39 years. Over time, the incidence of T1DM was stable in Hungary and Japan, and increased in Australia, Denmark, Finland, Scotland, South Korea, and Spain with annual changes ranging from 0·5% to 6·0%. Incidence of T2DM increased in 4 out of 8 jurisdictions (Denmark, Finland, Japan, and South Korea), with annual increases from 2·0% to 8·5%. The magnitude of increase in incidence of T2DM was greater in Asian than non-Asian jurisdictions. T2DM incidence was stable in Australia and Hungary, and decreased in Scotland and in Spain, with annual changes of -0·7% and -1·5%, respectively.

Interpretation
T2DM incidence increased in half of the jurisdictions, but increases were markedly greater in Asian than non-Asian jurisdictions. T1DM increased modestly across most jurisdictions. Changing patterns of incidence of T1DM and T2DM in young adults may call for greater research focus on young people with diabetes.