Decreasing incidence of pharmacologically and non-pharmacologically treated type 2 diabetes in Norway: a nationwide study

Abstract

Aims/hypothesis: This study aimed to examine recent time trends in the incidence and prevalence of type 2 diabetes in Norway.

Methods: In this Norwegian nationwide cohort study, we linked data from national registries with prospectively collected data on diabetes medication and diabetes diagnoses for all residents in Norway aged 30 to 89 years (>3.2 million people). We analysed trends in incidence and prevalence of type 2 diabetes from 2009 to 2014 by type of treatment, sex, age, education level and place of birth.

Results: During 15,463,691 person-years of follow-up from 2009 to 2014, we identified 75,496 individuals with new-onset type 2 diabetes. Of these, 36,334 (48%) were treated with blood-glucose-lowering drugs within 6 months of diagnosis. A low education level and being born in Asia, Africa or South America were significant risk factors for incident type 2 diabetes. While the prevalence of type 2 diabetes increased from 4.9% to 6.1% during the study period, the incidence decreased significantly from 609 cases per 100,000 person-years in 2009 to 398 cases per 100,000 in 2014, an annual reduction of 10.1% (95% CI -10.5, -9.6). A declining incidence was seen for both pharmacologically and non-pharmacologically treated type 2 diabetes, and in all subgroups defined by sex, age group, education level and place of birth.

Conclusions/interpretations: This nationwide study shows that, despite a decreasing incidence of type 2 diabetes in Norway, the prevalence continues to rise, probably due to diagnosis at a younger age and increased longevity.

Keywords: Incidence; Prevalence; Register-based study; Time trends; Type 2 diabetes.

Fig. 1

Time trends in proportion of people diagnosed with type 2 diabetes in the population aged 30–89 years in Norway from 2009 to 2014, in all participants and by treatment and sex. Black line, all participants; blue lines, men; red lines, women; solid lines, pharmacologically treated; dashed lines, non-pharmacologically treated

Fig. 2

Incidence trends in type 2 diabetes (a) Stratified by sex: blue line, men; red line, women; black line, all participants. Average annual per cent change in incidence rate: −10.1 (95% CI −10.5, −9.6). (b) Stratified by age group and sex: blue line, men; red line, women; solid line, age group 70–89 years; long dashed line, age group 50–69 years; short dashed line, age group 30–49 years. (c) Stratified by age for those treated with glucose-lowering medication within 6 months of diagnosis. (d) Stratified by age group for those not treated with glucose-lowering medication within the first 6 months of diagnosis. In (c) and (d): grey line, age group 30–49 years; orange line, age group 50–69 years; green line, age group 70–89 years. Data are presented as cases per 100,000 person-years with vertical bars representing 95% CI. T2D, type 2 diabetes

Fig. 3

Incidence trends for type 2 diabetes by place of birth and by education level. (a) By place of birth: red line, Norway; dashed grey line, Europe (except Norway); green line, Africa; dashed light-blue line, Asia; dashed dark-blue line, South America. Since there were very few cases from Oceania and North and Central America, to improve interpretability, data from these places of birth have not been included in the graph. (b) By education: red line, lower education level (≤10 years); black line, medium education level (11–13 years); dashed blue line, high education level (>13 years). Results stratified by education level are shown for individuals born in Norway only (85% of the source population), because of a high proportion of missing data on education level for people born abroad. Data are presented as cases per 100,000 person-years with vertical bars representing 95% CI. T2D, type 2 diabetes