Using a large aggregated health claims database, four key findings on the incidence of type 2 diabetes incidence in Bavaria, the largest German state, could be obtained. First, a decreasing incidence trend from 2012 to 2021, with a strong decrease from 2012 until 2017 followed by a less pronounced decline from 2018 to 2021, was observed for both sexes. Sex-specific ASIR decreased by 34.3% in men and by 35.7% in women from 2012 to 2021. Second, this downward trend was also observed for all 10-year age groups between 50 and 90 years, while the younger age groups 20–29, 30–39 and 40–49 years remained stable throughout for both sexes. Third, the median age at diagnosis decreased by 3.0 years for men and 4.8 years for women. Fourth, the incidence rate during the COVID-19 pandemic period (2020–2021) showed no change compared with the pre-pandemic period. This suggests that the incidence of type 2 diabetes was not affected by the first 2 years of the pandemic.

Our results correspond with previous international findings. A systematic review reporting type 2 diabetes incidence on a global level for the first time also revealed decreasing (36% of studies) or stable (30% of studies) incidence trends for most of the included high- and middle-income countries since 2010 [17, 18]. Of these, a higher proportion of the examined populations came from European countries (52%) than from non-European countries (41%) [17]. Compared with previous decades (starting in the 1960s) with increasing rates, a shift of direction in type 2 diabetes incidence trend in mainly European countries has occurred [17]. By additionally covering the pandemic period in our study, the observed decreasing incidence trend in Bavaria, Germany, not only aligns with these recent findings but allows for further assessment of the pandemic effect. In contrast to these recent international findings, a systematic analysis of the Global Burden of Disease Study 2019, which included 204 countries and territories, found an increase in type 2 diabetes incidence globally from 184.6 per 100,000 population in 1990 to 259.9 per 100,000 population in 2019 [19]. A recent study on incidence trends in Germany based on nationwide health claims data supports our results, also observing a decrease in incidence trend from 2014 to 2019 by 2.4% for women and 1.7% for men, with lower rates of 8.4 for men and 6.9 per 1000 people for women in 2014 and 7.7 for men and 6.1 per 1000 people for women in 2019 [20]. However, this study represents a short time period of 6 years and does not cover the pandemic period. Another recent study in Germany reported a decreasing type 2 diabetes incidence rate of 0.68% in 2015 and 0.57% in 2020, with slightly increased rates of 0.87% in 2021, but did not use any explanatory analysis to quantify the observed trend [21]. Goffrier et al, who also used health claims data, support our findings, reporting a nationwide 5% decrease in incidence in Germany over a short period of 3 years from 2012 to 2014. This study shows comparable incidence rates of 1630 per 100,000 people in 2012, 1600 per 100,000 people in 2013, and 1470 per 100,000 people in 2014 [22]. Further studies reporting incidence rates for Germany are either limited to very short periods, up to a maximum of 3 years, or have data based on selected health insurance funds, not allowing for any adequate inferences about the actual trend [22,23,24,25]. Most studies report incidence rates for the period before 2010, not representing current data [23,24,25]. Usually, slightly more men than women are affected by type 2 diabetes [26]; however, we reported an almost equal number of cases for men (50.4%) and women (49.6%) in our study. While recent prevalence data showed that more men (41.3%) are overweight than women (27.6%), obesity prevalence shows no difference in sex in Germany [27].

The downward trend of incidence observed could be due to robustness of preventive measures. A decrease in type 2 diabetes risk could be observed in Germany from 1997 to 1999 and 2008 to 2011, with the reductions in the consumption of red meat and waist circumference suggested as the main drivers [28]. However, meat consumption remained relatively stable from 2004 to 2014/2015 [29], as did the prevalence of overweight from 2012 to 2020 in Germany [27]. For most risk factors of type 2 diabetes, no major changes in the trend could be observed. While the prevalence of smoking decreased from 1995 to 2018 [30], the prevalence of obesity increased from 2012 to 2020 [27]. Also, physical inactivity levels are high in Germany [31]. Less than half of the adults (51.2% men and 44.8% women) reached the WHO recommendation of at least 2.5 h of aerobic physical activity per week before the pandemic [31] and 24% of adults reported reducing physical activity during the pandemic period in 2021 [32]. A potential reason for the decline in diabetes incidence might be sufficient screening efforts over the last 10 years. Studies show that people with screening-detected diabetes are diagnosed 3.3 to 4.6 years earlier than clinical-based detection [33, 34]. The observed decrease in the median age of diagnosis of 3.0 years for men and 4.8 years for women in our study supports this hypothesis of more effective screening by family physicians. Therefore, screening for type 2 diabetes seems to be an important step in diabetes prevention since cost-effective interventions (pharmacological and behavioural interventions) show benefits in preventing or delaying the progression of diabetes [35]. Glucose-lowering medications have been shown to improve all-cause and diabetes-related mortality for newly diagnosed type 2 diabetes compared to conventional treatment with diet [35]. Additionally, lifestyle interventions also reduce the progression of diabetes [35, 36]. Trials showed that lifestyle intervention in people with impaired glucose tolerance or impaired fasting glycaemia effectively reduced the incidence of diabetes by 28–58% compared with control groups over a period of 3 to 6 years [36].

Recent studies have hypothesised about the impact of COVID-19 on type 2 diabetes. Either a COVID-19 infection itself [37] or disease containment measures possibly altering the impact of lifestyle factors such as physical activity may increase the risk of type 2 diabetes by affecting glycaemic control and thus lead to an increase in type 2 diabetes [38, 39]. With no relevant changes in incidence in the first 2 years of the pandemic, our data suggest that patients continued to seek healthcare from their family physicians (and to a lesser extent with their specialists) [40]. However, type 2 diabetes often develops slowly over the course of several years [41], delaying the direct impact of the pandemic on incidence. Therefore, future monitoring is necessary to assess the long-term effect of the pandemic on diabetes incidence.

To accommodate the need for adequate diabetes monitoring, the German Diabetes Society has proposed a national diabetes registry [42]. Existing studies about diabetes development mainly focus on monitoring prevalence alone, with incidence rates rarely reported [1]. But incidence should also become a standard reporting metric for diabetes, since unlike prevalence, it allows the direct assessment of the effects of changes in risk factors, as it is not influenced by other factors, such as survival [17]. Recent prediction of the prevalence of type 2 diabetes in Germany projects an increase of 54–77% by 2040, with the incidence trend being the key factor in this increase [4]. Increased prevalence can coexist with decreasing incidence [20]. By monitoring and reporting both prevalence and incidence, a better understanding of the burden of type 2 diabetes can be achieved.

This study is the first to report the current 10-year incidence trend of type 2 diabetes for adults (>20 years) in Germany, effectively filling an important gap in diabetes monitoring, and providing a better understanding of the disease burden. Routinely collected health claims data were used in our analyses, encompassing all statutorily insured people in the state of Bavaria, with an insurance population of 11 million residents. These data represent a reliable data source and provide high accuracy for describing the incidence trend in Bavaria, the largest German state. In contrast to previous incidence studies of type 2 diabetes in Germany, which are mainly based on data from selected health insurance companies and short observation time periods [22,23,24], our study allows for a more extended analysis over 10 years with a complete regional sample. However, the data do not include the privately insured and typically high-income population (10–15% of the Bavarian population), who may have lower rates of diabetes than the general population [43]. Given the small share of this group of insurees in the total population, the present observed incidence rates may slightly overestimate population incidence. Additionally, this is one of the first studies reporting type 2 diabetes incidence in adults during the pandemic and comparing it to the pre-pandemic period in Germany. Only one study with a similar time period also showed decreasing incidence rates until 2020 with slightly increasing rates in 2021 in Germany [21].

General weaknesses of health claims data should be considered when interpreting the results [44]. Since claims data exist primarily for billing and reimbursement purposes, data might not always necessarily reflect just the medical burden, but also the coding and clinical practice of practitioners. This may also partly explain the seasonal patterns observed in the data. Studies investigating the seasonal patterns of the incidence of type 2 diabetes and changes in glycaemic control are inconsistent and can only partially explain the peaks in quarter four. Factors influencing seasonality include physical activity, dietary habits and ambient temperature [45,46,47]. In England, peak consultation occurred during hot weather waves [48], whereas in Hungary, incidence of type 2 diabetes was highest in March and lowest in August [46]. Additionally, physicians’ diagnostic coding errors could lead to misdiagnosis. To reduce any bias due to diagnostic accuracy, only cases with confirmed new diagnoses with the same ICD code twice in four consecutive quarters were included. Possible misclassification of type 2 diabetes was addressed in the sensitivity analyses. Additionally, the pandemic period only covers the first 2 years, 2020 and 2021. To investigate the later years of this global health emergency, data covering 2022 should be included as soon as reliable data are available. In contrast to quarterly data, weekly or monthly data during the pandemic could provide more information in relation to disease containment measures during the pandemic, similar to other studies primarily investigating the pandemic effect [49, 50].

To fully understand the epidemic of type 2 diabetes, reporting of incidence is crucial. Although prevalence seems to increase overall, a decreasing incidence trend in Germany from 2012 to 2021 could be observed in our study. This indicates a break in the upward trajectory of disease burden, potentially resulting from better screening efforts by the family physicians and thereby reducing the median age of diagnosis by 3–5 years for both sexes. No changes in incidence for the pandemic period in 2020 and 2021 relative to the pre-pandemic period were observed, indicating that this group of patients continued to seek healthcare services even during an extraordinary healthcare crisis. Reasons for the declining incidence trend need further investigation using appropriate data sources, and continuous monitoring of the incidence is necessary to identify the long-term trend and potential effects of the pandemic on diagnoses.