GRAPHICAL ABSTRACT

INTRODUCTION

Diabetes mellitus is a major global public health challenge and a leading contributor to premature mortality. The Global Burden of Disease Study has consistently demonstrated its growing impact on mortality and disability-adjusted life years [1]. Individuals with diabetes experience approximately twice the risk of all-cause mortality compared with those without the disease, largely because of its strong association with cardiovascular disease (CVD) [2], which results in persistently shorter life expectancy [3,4].

Of particular concern is the rising incidence of type 2 diabetes at younger ages, as the condition was once predominantly observed in older adults [4]. Early-onset type 2 diabetes is associated with prolonged exposure to hyperglycemia and related complications, leading to greater cumulative health loss [5]. This metabolic burden heightens the risk of premature death, for which years of life lost (YLL) is a key metric that quantifies its impact. A large multinational study reported that individuals diagnosed in their 30s may lose up to 14 years of life compared with their non-diabetic peers, with YLL decreasing with older age at diagnosis but remaining clinically important across all age groups [3].

Korea mirrors these global patterns, with a rapid rise in diabetes prevalence and overall disease burden [6,7]. Diabetes is now a leading cause of death, and although the average age at death among individuals with diabetes has increased—narrowing the mortality gap relative to the non-diabetic population—it remains a major contributor to premature mortality, particularly when comorbidities such as hypertension or dyslipidemia are present [8]. Consistent with these patterns, a recent study showed that, as of 2020, diabetes was the leading cause of disease burden among Koreans [9].

Accurate assessment of disease burden is essential for informing public health interventions. Among available metrics, YLL, which quantifies premature mortality, plays a central role and requires precise attribution of cause-specific deaths [10]. In this context, we examined temporal trends in YLL attributable to diabetes in Korea from 2008 to 2019 and identified specific causes of death that contributed to these changes.

METHODS

Data source and study design

This study utilized data from the Korean National Health Insurance Service-National Sample Cohort (NHIS-NSC), a nationwide, population-based cohort established by the NHIS. Korea operates a single-payer healthcare system that covers approximately 98% of the population. To support research, the NHIS developed the National Health Information Database (NHID); however, because of its large volume and strict privacy requirements, direct access is limited. To enhance accessibility while maintaining representativeness, the NHIS established the NHIS-NSC, a comprehensive sample database created by stratifying the population into 1,476 strata based on age, sex, eligibility status, and income level. The database includes detailed sociodemographic information, medical reimbursement claims (including International Classification of Diseases, 10th Revision [ICD-10], and Anatomical Therapeutic Chemical [ATC] classification codes), and mortality data [11]. This study included all individuals in the NHIS-NSC who maintained continuous NHIS eligibility from January 1, 2008, to December 31, 2019. The study protocol was reviewed and approved by the Institutional Review Board of Ajou University Hospital, Suwon, Republic of Korea (approval No. AJOUIRB-EX-2025-340), and the requirement for informed consent was waived.

Ascertainment of diabetes and death

Diabetes was defined as the presence of an ICD-10 diagnosis code for diabetes (E10–E14) together with a prescription for glucose-lowering medications (ATC code A10). Mortality data were obtained from the National Death Registry, which assigns a unique identification number to all participants. Underlying causes of death were classified using ICD-10 codes. In addition to all-cause mortality, cause-specific deaths were grouped into six mutually exclusive categories: (1) cancer (C00–C97), (2) CVD (I00–I99), (3) diabetes (E10–E14), (4) infections (A00–A99, J12–J18), (5) kidney disease (N00–N07, N17–N19, N25–N27), and (6) other causes.

Statistical analyses

Annual trends in standardized mortality ratios (SMRs) from 2008 to 2019 were analyzed separately by sex. SMRs for overall mortality were estimated using individuals without diabetes as the reference group for the same period. The expected number of deaths was calculated through indirect standardization, adjusting for age in 5-year intervals. SMRs were computed as the ratio of observed to expected deaths, with 95% confidence intervals (CIs). An SMR was considered statistically significant if its 95% CI did not include 1.0, indicating a departure from the mortality rate observed in the reference population.

Temporal patterns in survival disparities were examined across three predefined periods: 2008–2011, 2012–2015, and 2016–2019. To ensure stability in mortality estimates for individuals with diabetes, the overall study period (2008–2019) was divided into these three consecutive 4-year intervals. This stratification allowed for an adequate number of events in each interval and reduced random fluctuations from small year-to-year variations, thereby enabling more reliable comparisons of temporal mortality trends. Life expectancy for individuals with and without diabetes was estimated using abridged life tables stratified by sex. Age-specific mortality rates were converted into life-table probabilities of dying, with the probability of death set to 1.0 for the terminal age group (≥90 years). Life expectancy at ages 40, 50, 60, 70, and 80 years was also calculated to evaluate the long-term survival impact of diabetes across different life stages, with 95% CIs provided for each estimate. In this study, YLL was defined as the difference in life expectancy between individuals with and without diabetes. YLL estimates were calculated separately for males and females within each period. Arriaga’s decomposition method was then used to partition the life expectancy gap into contributions from specific causes of death, thereby identifying the primary contributors to excess mortality among individuals with diabetes. All analyses were performed using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA) and R version 4.0.3 (R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

Between 2008 and 2019, SMRs for individuals with diabetes declined substantially in both sexes. Among males, the SMR decreased from 2.19 (95% CI, 2.05 to 2.32) to 1.55 (95% CI, 1.47 to 1.64), representing a 29% relative reduction. Among females, the SMR declined from 2.04 (95% CI, 1.90 to 2.18) to 1.36 (95% CI, 1.28 to 1.44), corresponding to a 33% relative reduction. Although SMRs remained consistently higher in males throughout the study period, the larger relative reduction observed in females indicates a more pronounced improvement in diabetes-related mortality in this group (Fig. 1, Supplemental Table S1).

At all index ages from 40 to 80 years, life expectancy increased between 2008–2011 and 2016–2019 for both sexes, with larger absolute gains in individuals with diabetes than in those without. At age 40, life expectancy among males with diabetes increased from 32.53 to 37.81 years, compared with an increase from 40.89 to 43.51 years among males without diabetes. In females, corresponding estimates rose from 39.41 to 43.77 years and from 46.92 to 48.98 years, respectively (Table 1). As a result, diabetes-attributable YLL at age 40 declined from 8.36 to 5.70 years in males and from 7.51 to 5.21 years in females, representing relative reductions of 32% and 31%, respectively. Similar trends were seen at older ages, although the absolute magnitude of YLL was smaller with advancing age. For example, at age 80, YLL decreased from 1.83 to 1.32 years in males and from 2.12 to 1.60 years in females (Fig. 2, Supplemental Table S2).

The composition of YLL by cause of death varied by sex and age. At age 40, the largest relative reductions in YLL between 2008–2011 and 2016–2019 were observed for diabetes (–40% in males and –46% in females), CVD (–37% in males and –52% in females), and kidney disease (–33% in both sexes). YLL attributable to cancer declined modestly (–28% in males and –13% in females), whereas YLL from infections increased slightly (21% in males and 28% in females). At age 80, overall YLL values were substantially lower, but the pattern of change differed. In males, the greatest relative reductions were noted for CVD (–57%) and cancer (–48%), followed by diabetes (–24%). In females, CVD (–63%) and diabetes (–44%) showed the largest decreases, whereas YLL from cancer increased sharply from 0.11 to 0.37 years, representing an approximately 236% increase (Fig. 2, Supplemental Table S2).

DISCUSSION

In this nationwide analysis of the mortality burden attributable to diabetes in Korea from 2008 to 2019, we found a substantial decline in YLL, accompanied by gains in life expectancy and reductions in SMRs. The most notable reductions in YLL were observed for deaths due to diabetes, CVD, and kidney disease.

Across various countries, SMRs for individuals with diabetes have ranged from approximately 1.0 to 3.5 times those of individuals without diabetes, although temporal patterns differ by country [12-15]. In Korea, SMRs have shown a consistent downward trend, reaching 1.55 in males and 1.36 in females in 2019. Nevertheless, individuals with diabetes continue to experience shorter life expectancy than those without diabetes, reflecting the ongoing burden of diabetes-related complications and premature mortality. Similar findings have been reported elsewhere. In Finland, the life expectancy gap was 4.0 years for males and 3.2 years for females; in Australia, 4.1 years for males and 3.9 years for females [4]; and in China, individuals with diabetes or prediabetes at age 40 had an average life expectancy 4.2 years shorter than those with normoglycemia [16]. In Korea, the YLL at age 40 remained substantial, at 5.70 years for males and 5.21 years for females.

Although YLL in Korea remains significant, it has decreased by approximately 30% over the past decade. The improved outcomes likely reflect system-level enhancements in the quality of diabetes care. Earlier diagnosis, better glycemic and lipid control, and the broad adoption of novel pharmacotherapies—such as sodium-glucose cotransporter 2 (SGLT2) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists—have strengthened risk factor management. A key driver has been the National Diabetes Quality Assessment Program (NDQAP), a nationwide initiative launched by the Korean government. By incentivizing continuity of care, regular monitoring, and adherence to treatment guidelines at the primary care level, NDQAP has been associated with meaningful reductions in severe diabetes complications and all-cause mortality [17]. Collectively, these improvements likely contributed to the decline in YLL observed during the study period.

Substantial disparities in YLL by age and sex remain. In this study, life expectancy at age 40 among individuals with diabetes was 5.7 years lower for males and 5.2 years lower for females compared with their non-diabetic counterparts. Although these differences narrowed with age, the gap persisted at age 80. This pattern suggests that younger adults diagnosed with diabetes carry a disproportionate burden of premature mortality. The long-term consequences of early-onset diabetes are well documented; prior studies have shown that diagnosis at age 30 may reduce life expectancy by as much as 14 years [3]. Our findings reinforce that prolonged exposure to hyperglycemia, earlier onset of complications, and potential delays in diagnosis or suboptimal early management likely contribute to the higher YLL observed among younger adults. These trends highlight the urgent need for public health strategies focused on early detection, prevention, and timely intervention—especially among younger individuals—to reduce long-term mortality risk and close the persistent life expectancy gap.

The substantial age- and sex-related disparities in YLL observed in Korea likely stem from a complex interplay of demographic, biological, behavioral, and socioeconomic factors. Korea’s rapid population aging—especially among females, who have one of the longest life expectancies within the Organization for Economic Cooperation and Development—has increased the absolute burden of age-related deaths. Lower screening participation among older or low-income females further exacerbates these disparities [18,19]. Persistent inequalities in education, income, and healthcare access also contribute to the widening gap in YLL between sexes and across age groups [20,21]. These findings underscore the need for targeted, age- and sex-specific public health strategies that emphasize early detection, preventive efforts, and equitable access to high-quality care to reduce premature mortality and narrow the life expectancy gap in Korea. Additional research is required to examine these disparities in greater detail and identify specific factors driving the observed trends.

The shifting pattern in the cause-specific composition of YLL was particularly evident among older adults. As YLL attributable to vascular causes declined, cancer and infection emerged as increasingly prominent contributors. Among males aged 80 years, cancer-related YLL decreased by 48%, whereas in females it increased more than three-fold. In contrast, infection-related YLL increased by 82% in males and rose slightly among older females. The sharp rise in cancer-related YLL among older females likely reflects Korea’s rapidly aging female population and persistent disparities in cancer prevention and care. Mortality from breast, pancreatic, and ovarian cancers remains stagnant or increasing in this group, contributing disproportionately to YLL [22,23]. Despite expansions in national screening, participation remains lower among older, rural, and low-income females, leading to later diagnoses and poorer outcomes [19,24]. Additionally, metabolic risk factors such as abdominal obesity and glucose intolerance—both highly prevalent in older females—further elevate cancer risk [25]. Evidence also suggests that older females receive fewer standard treatments, including surgery and adjuvant therapy, which can lead to poorer survival [26-28]. These demographic, behavioral, and healthcare factors likely underlie the observed increase in cancer-related YLL among older females. Collectively, these findings reflect an epidemiological transition in the burden of diabetes-related mortality, similar to trends seen in other high-income countries such as the United States and Japan [29,30]. Aging, immunosenescence, multimorbidity, and polypharmacy may further exacerbate vulnerability to non-vascular causes in elderly individuals with diabetes, particularly among females [31,32].

This study has several limitations. First, the use of administrative claims data limited our ability to assess clinical risk factors such as glycemic control, obesity, lipid levels, and smoking status, all of which may confound mortality outcomes. Second, the identification of diabetes and comorbidities relied on diagnostic and procedural codes and may therefore be subject to misclassification or underascertainment. Third, diabetes was defined as the presence of both a diagnostic code and a prescription code for glucose-lowering medication recorded during the same period. However, we were not able to apply additional criteria related to treatment persistence, such as requiring at least two prescriptions or a minimum duration of therapy. Consequently, short-term prescriptions or individuals with prediabetes may have been included. Such potential misclassification likely resulted in an underestimation of the true difference in life expectancy between the diabetes and non-diabetes groups. Lastly, although this study provides valuable insights into trends in YLL attributable to diabetes in Korea—potentially influenced by the introduction of SGLT2 inhibitors and GLP-1 receptor agonists—we were unable to conduct a detailed pre- and post-introduction comparison of life expectancy and mortality due to data limitations. Future studies with comprehensive longitudinal data are needed to further clarify these trends and elucidate the impact of these therapies on long-term survival. Despite these limitations, the use of large, nationally representative data allowed for robust estimation of temporal patterns in YLL and its contributing causes.

In conclusion, Korea has made meaningful progress in reducing mortality attributable to diabetes, with notable declines in YLL driven by reductions in major metabolic and vascular causes. However, persistent age- and sex-related disparities remain, and the increasing contribution of cancer and infection to YLL underscores the need for tailored, age- and cause-specific strategies. Strengthening early detection, expanding access to novel therapies, and integrating chronic disease management across the life course will be essential for further reducing avoidable mortality and closing the life expectancy gap among people living with diabetes.

Supplementary Material

Article information

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

ACKNOWLEDGMENTS

This study used National Health Insurance Service-National Sample Cohort (2002–2019) data (NHIS-2025-08-2-021) provided by the National Health Insurance Service (NHIS).

AUTHOR CONTRIBUTIONS

Conception or design: K.H.H., D.J.K. Acquisition, analysis, or interpretation of data: K.H.H., D.J.K. Drafting the work or revising: D.H.S., K.H.H., D.J.K. Final approval of the manuscript: D.H.S., K.H.H., D.J.K.

Fig. 1.

Trends in age-standardized mortality ratios, 2008–2019. (A) Male and (B) female.

Fig. 2.

Trends in absolute years of life lost attributable to specific causes among individuals with diabetes, 2008–2019. (A) Male and (B) female. CVD, cardiovascular disease.

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Figure & Data

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