Long-term trends of municipal-level variation in ischemic heart disease mortality in Korea and Japan, 1999–2023
H Kim, M Cho, H Lee, T OkuiAbstract
Background
Korea and Japan have achieved some of the lowest age-standardized death rates (ASDRs) from ischemic heart disease (IHD) globally, with substantial long-term reductions in mortality. However, it remains unclear whether these national-level improvements have been accompanied by corresponding reductions in subnational geographic disparities. Long-term comparative evidence on municipal-level variation in IHD mortality remains limited.
Purpose
To examine long-term trends in IHD mortality and municipal-level regional variation in Korea and Japan from 1999 to 2023, including differences between metropolitan and non-metropolitan municipalities.
Methods
National mortality data from Korea and Japan were analysed for 1999–2023. IHD deaths were identified using ICD-10 codes I20–I25. The study included approximately 250 administrative districts in Korea and 1,800 municipalities in Japan. ASDRs were calculated using direct standardization with the 2015 Japanese population as the standard. Standardized mortality ratios (SMRs) were computed annually based on national sex- and age-specific mortality rates. Regional variation was assessed using the standard deviation (SD) of municipal-level ASDRs and SMRs. Municipalities were classified as metropolitan or non-metropolitan.
Results
National ASDRs declined markedly in both countries (Korea: 64.6 in 1999 to 39.9 in 2023; Japan: 99.5 to 48.5). However, trends in regional variation diverged. In Korea, absolute variation (SD of ASDRs) decreased overall, while relative variation (SD of SMRs) declined until the mid-2010s and re-expanded after 2020. In Japan, both absolute and relative variation increased gradually throughout the study period. When municipalities were classified as metropolitan or non-metropolitan, recent increases in variation in Korea were more pronounced in non-metropolitan areas, whereas in Japan variability rose in both settings, with a greater increase in metropolitan regions. Thus, substantial municipal-level heterogeneity persisted despite sustained national mortality declines.
Conclusion
Even in countries with the lowest IHD mortality rates worldwide, regional disparities have not been fully resolved and, in some periods, have widened. Declines in national ASDRs were not consistently accompanied by reductions in municipal-level variation. Continuous fine-scale monitoring and geographically tailored prevention strategies are important to ensure that improvements in cardiovascular mortality are distributed more equitably across regions.Trends in IHD ASDR variation, 1999–2023IHD SMRs in metropolitan vs non-metropolitan