Diabetes is a serious chronic disease characterized by elevated blood glucose levels, resulting from either insufficient insulin production or impaired insulin action. Globally, diabetes poses a significant health burden, affecting hundreds of millions of individuals and placing a strain on healthcare systems worldwide. The World Health Organization (WHO) recognizes diabetes as one of the three target diseases in its Global Action Plan for the Prevention and Control of Noncommunicable Diseases (NCDs), highlighting its importance as a public health concern. Despite the growing awareness of the diabetes epidemic and the availability of established prevention and management strategies, the global prevalence of diabetes continues to rise, presenting a formidable challenge to health professionals and policy makers. This increasing prevalence, particularly driven by type 2 diabetes, necessitates an urgent need for a comprehensive understanding of the diabetes burden and its underlying risk factors. The current study, conducted as part of the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021, aims to address this need by providing location-specific, age-specific, and sex-specific estimates of diabetes prevalence and burden from 1990 to 2021. The analysis also examines the contribution of key risk factors, particularly high body mass index (BMI), to the rising burden of type 2 diabetes. Finally, projections of diabetes prevalence through 2050 are provided to inform future policy interventions and resource allocation.

Previous research has extensively documented the global burden of diabetes and its impact on healthcare systems and societies. The GBD 2019 study reported that diabetes was the eighth leading cause of death and disability worldwide, affecting nearly 460 million individuals. The International Diabetes Federation (IDF) estimates that by 2021, the number of people with diabetes had increased to 537 million, resulting in a global healthcare expenditure exceeding US$966 billion. The IDF also projects that healthcare expenditures associated with diabetes will continue to rise, reaching more than $1054 billion by 2045. Despite these alarming figures, the 2016 NCD Risk Factor Collaboration (NCD-RisC) study revealed a stark reality: the probability of meeting global targets to halt the rising diabetes prevalence by 2025 was extremely low, highlighting the urgency for effective intervention strategies. The Lancet Commission on diabetes, published in 2020, further emphasized the disproportionate burden of diabetes on low- and middle-income countries (LMICs), stating that 80% of diabetes cases occur in these regions. The Commission highlighted the need for accurate and focused data to guide the development of effective programs targeting key risk factors and addressing the socioeconomic challenges that contribute to the diabetes epidemic in LMICs. This study responds to these calls for action by providing detailed estimates of diabetes prevalence and burden, stratified by location, age, and sex. By leveraging the updated methodological framework of GBD, this study offers a comprehensive view of the diabetes landscape, including the drivers of the disease and their changes over time, and forecasts global and location-specific diabetes prevalence through 2050.

The GBD 2021 study employed a robust methodological framework to generate comprehensive estimates of diabetes prevalence and burden. The analysis incorporated data from a variety of sources, including: 1) vital registration data, 2) verbal autopsy reports, 3) scientific literature, 4) survey microdata, and 5) insurance claims. These data sources were rigorously reviewed and standardized to ensure consistency and reliability. The analysis was conducted for 204 countries and territories, across 25 age groups, and separately for males and females. The study focused primarily on diabetes prevalence and burden, as these metrics are particularly relevant for characterizing type 2 diabetes and capturing the rapid global rise of the disease. Mortality estimates were also generated but were presented in the appendix due to their secondary importance. The analysis incorporated a variety of statistical models, including: 1) Cause of Death Ensemble model (CODEm) for estimating deaths due to diabetes, 2) Bayesian meta-regression modelling tool, DisMod-MR 2.1, for estimating total and type 1 diabetes prevalence, and 3) a comparative risk assessment framework for estimating the risk-attributable type 2 diabetes burden for 16 selected risk factors. The CODEm model incorporated 25,666 location-years of data from vital registration and verbal autopsy reports to estimate deaths due to diabetes. The model included separate total (including both type 1 and type 2 diabetes) and type-specific models. A log-linear regression model was developed to predict the type-specific proportion of deaths among those coded to unspecified diabetes, using data that specified the diabetes type. The model included country-years with more than 50% of deaths due to diabetes coded as being due to type 1 or type 2 diabetes, as well as country-years with type-specific coding where 70% or more of type-specific deaths for people older than 25 years were coded as type 2 diabetes. The prevalence of obesity was included as a covariate to redistribute deaths accordingly to type 1 or type 2 diabetes. The DisMod-MR 2.1 model analyzed 1,527 location-years of data from the scientific literature, survey microdata, and insurance claims to estimate total and type 1 diabetes prevalence. Type 2 diabetes estimates were computed by subtracting type 1 diabetes from total estimates. The model included predictive covariates such as proportion of livebirths in women aged 35 years and older, maternal education, Healthcare Access and Quality Index (HAQ Index), prevalence of obesity, and year. The comparative risk assessment framework analyzed 16 detailed risk factors for diabetes, including: ambient particulate matter pollution, household air pollution from solid fuels, smoking, second-hand smoke, high alcohol use, high BMI, diet low in fruits, diet low in vegetables, diet low in whole grains, diet high in red meat, diet high in processed meat, diet high in sugar-sweetened beverages, diet low in fiber, low physical activity, high air temperature, and low air temperature. These risk factors fall into six categories: environmental or occupational, tobacco use, high alcohol use, high BMI, dietary risks, and low physical activity. The framework used meta-analyses to estimate the relative risk of diabetes as a function of risk factor exposure and calculated population attributable fractions (PAFs) to quantify the proportional reduction in diabetes that would occur if exposure to the given risk factor was reduced to the theoretical minimum risk exposure level (TMREL). PAFs were multiplied by DALYs to estimate the risk-attributable burden. Finally, a regression model was used to forecast type 1 and type 2 diabetes prevalence through 2050, using Socio-demographic Index (SDI) and high BMI as predictors, respectively.

The GBD 2021 study revealed a substantial global burden of diabetes, with an estimated 529 million people living with the disease in 2021. The global age-standardized total diabetes prevalence was 6.1%, with significant regional variations. North Africa and the Middle East had the highest age-standardized prevalence at 9.3%, while Oceania had the highest regional prevalence at 12.3%. Qatar had the highest country-level prevalence, reaching 76.1% in individuals aged 75-79 years. The analysis revealed that type 2 diabetes accounted for the vast majority of diabetes cases worldwide, representing 96.0% of all diabetes cases in 2021. The global age-standardized diabetes DALY rate was 915.0 per 100,000, with rates exceeding 1,000 per 100,000 in four GBD super-regions: Latin America and Caribbean, sub-Saharan Africa, north Africa and the Middle East, and south Asia. The study also identified high BMI as the primary risk factor for type 2 diabetes worldwide, accounting for 52.2% of global type 2 diabetes DALYs in 2021. The contribution of high BMI to type 2 diabetes DALYs has increased significantly over time, rising by 24.3% between 1990 and 2021. The analysis further revealed that dietary risks combined accounted for 25.7%, environmental or occupational risks combined accounted for 19.6%, tobacco use accounted for 12.1%, low physical activity accounted for 7.4%, and alcohol use accounted for 1.8% of type 2 diabetes DALYs in 2021. The projections for 2050 indicate a significant increase in diabetes prevalence, with more than 1.31 billion people projected to have diabetes globally, driven primarily by rising rates of obesity. The age-standardized total diabetes prevalence is expected to exceed 10% in two super-regions: north Africa and the Middle East (16.8%) and Latin America and Caribbean (11.3%). The age-standardized diabetes prevalence rate is projected to surpass 10% in 89 countries and territories, and to exceed 20% in 24 countries and territories. Every country and territory in three regions – Oceania, north Africa and the Middle East, and central Latin America – is projected to have a diabetes prevalence rate exceeding 10% by 2050. The projected increase in total diabetes prevalence is expected to be driven by type 2 diabetes, with the age-standardized global prevalence of type 2 diabetes projected to rise by 61.2%, affecting more than 1.27 billion people in 2050. The age-standardized global prevalence of type 1 diabetes is expected to increase by 23.9% in 2050.

The findings of the GBD 2021 study underscore the escalating global diabetes burden and its far-reaching consequences. The study's projections suggest that diabetes will continue to pose a major public health threat for decades to come, particularly in regions with high prevalence rates and rapidly growing populations. The study highlights the need for a multi-pronged approach to address the diabetes epidemic, focusing on: 1) prevention, 2) early diagnosis, 3) effective management, and 4) improved access to healthcare services. The study's findings provide strong evidence for the need to address the growing epidemic of obesity, particularly in regions with high BMI-related type 2 diabetes DALYs. Strategies to promote healthy lifestyles, improve access to healthy food options, and address social determinants of health are critical to limiting the rise in obesity and preventing the development of type 2 diabetes. The study also emphasizes the importance of early diagnosis and effective management of both type 1 and type 2 diabetes to prevent complications and improve health outcomes. Early diagnosis and treatment can delay or prevent the onset of complications associated with diabetes, such as neuropathy, diabetic foot, lower limb amputation, and vision loss due to retinopathy. Improving access to healthcare services, particularly in LMICs, is crucial for providing timely and effective diabetes care. These services include access to medication, regular monitoring, patient education, and support systems to manage the disease and its complications. The study's detailed estimates and forecasts provide valuable data to inform policy interventions and resource allocation. By understanding the geographical and demographic patterns of diabetes, as well as the contribution of key risk factors, policymakers can develop targeted strategies to address the specific challenges faced by different populations. This study serves as a call to action for the global health community to prioritize efforts to control the diabetes epidemic through prevention, early diagnosis, effective management, and equitable access to healthcare.

The GBD 2021 study provides a comprehensive assessment of the global diabetes burden, highlighting the escalating prevalence, significant regional variations, and the critical role of high BMI as a risk factor for type 2 diabetes. The projections suggest a substantial increase in diabetes cases by 2050, underscoring the urgent need for effective interventions. The study emphasizes the importance of a multi-pronged approach that addresses the root causes of diabetes, including obesity, as well as promotes early diagnosis, effective management, and improved access to healthcare services.

The study acknowledges several limitations that might impact the interpretation or generalizability of the results. First, the study excluded studies that relied on self-reported diabetes status without validation through blood glucose tests. This omission might have resulted in a slight underestimation of diabetes prevalence in some populations. Second, the study did not explicitly estimate gestational diabetes, which is captured under a different disease category in GBD. Third, the study did not include rarer forms of diabetes, such as monogenic diabetes, due to limited data availability. Fourth, the study assumed that all individuals younger than 15 years have type 1 diabetes. However, growing evidence suggests that type 2 diabetes can occur in younger individuals, and future research should address this issue. Finally, the study did not capture all known risk factors for type 1 diabetes, relying on SDI as a proxy for better access to care. Further research focused on specific risk factors for type 1 diabetes is needed. These limitations highlight the need for ongoing research and data collection to improve the accuracy and comprehensiveness of diabetes estimates and to inform effective interventions.