Type 2 diabetes in Norway 2009–2021: Have declining incidence rates continued?

Aims/hypothesis To investigate updated trends in the incidence and prevalence of diagnosed type 2 diabetes in Norway by age, sex, country of birth and education.

A nationwide cohort study using registries on primary and specialist healthcare, dispensed drugs, and demographic factors in Norway. We analysed incidence trends 2009-2021 using Poisson regression and JoinPoint.

During 2009–2021, 195 935 incident type 2 diabetes cases were identified. After a decline in incidence 2009–2014, the incidence was largely stable over time, with a suggestive upward trend 2019–2021. The overall incidence rates were 651 per 100 000 person-years in 2009 and 530 per 100 000 in 2021. There were 165 432 prevalent cases of type 2 diabetes in 2009 (5.5% of the population), consistently increasing throughout the study period to a peak at 259 017 (7.5%) in 2021. The time trends were largely consistent across age, sex, country of birth and education. Inhabitants with lower education and born in Asia or Africa had substantially higher incidence and prevalence than those with higher education and born in Norway or other continents, respectively. Conclusions/interpretation The previously described decline in incidence of diagnosed type 2 diabetes during 2009– 2014 was not sustained, and prevalence continued to increase throughout 2009–2021. What is already known about this subject? The incidence rate of type 2 diabetes in Norway and several other countries decreased from 2009–2014, despite an ongoing increase in prevalence. What is the key question? Has the decrease in incidence rate of type 2 diabetes in Norway continued after 2014? What are the new findings? The incidence rate of type 2 diabetes in 30–89-year-old residents in Norway was relatively stable from 2015–2021, with a suggestive increase from 2019–2021, largely consistent by sex, age, education and country of birth. The prevalence continued to increase. How might this impact on clinical practice in the foreseeable future? Both incidence and prevalence are important for shorter term health care planning in an ageing population and to understand time trends. Competing Interest Statement PLDR reports participation in research projects funded by pharmaceutical companies (one on diabetes drug), all regulator-mandated Phase IV studies (PASS) unrelated to the submitted work, with all funds paid to their institution (no personal fees). EQ performs contract studies, for which all funds are paid to her institution (Oslo University Hospital) and has received renumeration for lectures from Novo Nordisk and Lilly. LCS, LBH, GT, IJB and HLG report no conflict of interest. Funding Statement POSDIT funding for position of LBH from South-Eastern Norway Regional Health Authority. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study is part of the DIANOREG project (Population-based register study of diabetes (POSDIT) in Norway). The study was approved by the Regional committees for medical and health research ethics, South East B (REK 28748 (2019/1175). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes Social media: “Type 2 diabetes incidence in Norway: Decline halted – incidence largely stable since 2015” (@c_stene) Data Availability Data are accessible to authorised researchers after ethical approval and application to https://helsedata.no/en/, administered by the Norwegian Institute of Public Health.