PUBLIC HEALTH
Introduction,,
Over the past 30 years, Japan has made remarkable strides in population health, emerging as one of the world's leading nations in longevity. Older Japanese individuals, in particular, have better health outcomes compared with those in countries with similar socioeconomic status.1 Our previous analysis up to 2015, however, revealed a notable slowdown in these advances since 2000.2 This slowdown coincides with persistent health disparities across prefectures and a surge in non-communicable diseases (NCDs) associated with an ageing population. The multiphase, long-term, national health promotion initiative, Health Japan implemented by the Ministry of Health, Labour and Welfare, has had a crucial role in addressing these challenges. An assessment of its second phase, using pre-COVID-19 pandemic data, showed notable decreases in age-standardised mortality from major NCDs such as cancer and cardiovascular diseases over nearly a decade.3 Nevertheless, there has been little progress in other chronic conditions and in narrowing the health disparities across prefectures. Additionally, challenges such as the scarcity of data on non-fatal disease burdens associated with longevity4 and the absence of comprehensive health metrics, which encompass a wide range of health aspects and enable comparative analysis, continue to obstruct the prioritisation of health policies and interventions necessary for revitalising Japan's health progress in a rapidly ageing society where many health issues intersect.
Methods
Overview
GBD 2021 methodology has been published previously.We used GBD 2021 data to assess the burden of diseases and injuries in Japan's 47 prefectures from 1990 to 2021, including the COVID-19 pandemic.This latest GBD round represents substantial methodological improvements over previous iterations, including enhanced age-specific data collection for mortality in children younger than 5 years, refined estimation methods for rare causes of death, and, for the first time, the inclusion of COVID-19 burden estimates.Additionally, risk factor analyses underwent substantial methodological advancement through standardisation of relative risk estimation, implementation of new burden-of-proof risk function methods, improved specification of the mediation matrix, and re-evaluation of theoretical minimum risk exposure levels for 19 risk factors—primarily dietary risks, high systolic blood pressure, high LDL cholesterol, and high BMI.9 The analysis included 371 causes and 88 risk factors, using 1474 data sources for japan. Risk factors are divided into metabolic, environmental and occupational, and behavioural risks.
Mortality estimation
National and prefectural mortality data from 1990 to 2021 were obtained from Japan's vital statistics system. Data were standardised to match the GBD 2021 cause classification, and ill-defined causes were redistributed using established algorithms.7 Mortality estimates were generated using the Cause of Death Ensemble model (CODEm), which combines multiple models to enhance predictive validity.7 YLLs were calculated by multiplying each death by the GBD 2021 reference life expectancy.
Non-fatal health outcome estimation
Non-fatal health outcomes were estimated using various data sources, including observational studies, government surveys, and COVID-19 epidemiological studies. Prevalence and incidence were estimated using Bayesian Meta-Regression Disease Model (DisMod-MR 2.1) or spatiotemporal Gaussian process regression (ST-GPR).8 DisMod-MR 2.1 integrates data variability and uncertainty, while ST-GPR handles spatial and temporal correlations.8 YLDs were calculated by multiplying the prevalence of sequelae by their respective disability weights.
Calculation of DALYs and HALE
DALYs were computed by summing YLLs and YLDs for each cause. HALE was estimated using age-specific mortality rates and YLDs per capita, following the Sullivan method.
Effect of the COVID-19 pandemic on disease burden
GBD 2021 estimated several new causes, such as COVID-19 (including post-COVID-19 condition, also known as long COVID) and other COVID-19 pandemic-related outcomes. Drawing from multiple data sources—with Japanese mortality statistics specifically derived from the Ministry of Health, Labour and Welfare's excess mortality research group reports13 and non-fatal outcomes from various surveys and peer-reviewed literature—COVID-19 deaths and morbidity were estimated using a susceptible-exposed-infectious transmission model, accounting for factors such as vaccination and antiviral treatments.8 YLLs were calculated by multiplying each COVID-19 death by the reference life expectancy.10 Non-fatal outcomes included acute sequelae of COVID-19 and long COVID (ie, post-acute sequelae). Daily infections and hospital admissions were tracked to estimate YLDs for acute sequelae, applying corresponding disability weights.8 Long COVID prevalence was estimated using DisMod-MR 2.1, and YLDs were calculated based on symptom clusters.8 Estimates for other COVID-19 pandemic-related outcomes were derived from an analysis of all-cause excess mortality from 2020 to 2021, using a counterfactual approach.
Comparative risk assessment
The comparative risk assessment framework estimated the relative risks of outcomes as a function of risk factor exposure. Data were sourced from scientific literature and government statistics. Theoretical minimum risk exposure levels were used to calculate population attributable fractions, which were then applied to the disease burden to estimate attributable burden.9
Decomposition of life expectancy
The decomposition of life expectancy was conducted using a three-step approach designed to quantify the contributions of specific causes of death, explained in detail elsewhere.7 The first step involves breaking down the difference in life expectancy by age. The second step further subdivides these contributions by age and cause. Finally, these cause-age-specific contributions are cumulated across age groups to assess the cause-specific impacts on the overall variance in life expectancy.
Role of the funding source
The funder of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report.
Results
All estimates, excluding annualised rate of change analyses, are available for visual exploration via the online visualisation tool GBD Compare, and downloadable format through the GBD Results Tool.
In Japan, the life expectancy at birth in 2021 was 85·2 years (95% UI 85·1–85·2), representing an increase of 5·8 years compared with that in 1990 (79·4 years [79·3–79·4]; appendix 1 pp 3, 20–21). For females, life expectancy reached 88·1 years (88·0–88·2) in 2021, an increase of 5·8 years since 1990 (82·3 years [82·2–82·3]). For males, life expectancy was 82·2 years (82·1–82·2) in 2021, an increase of 5·9 years since 1990 (76·2 years [76·2–76·3]; figure 1; appendix 1 pp 22–25). The disparity in life expectancy between the prefectures with the highest and lowest values increased from 2·3 years in 1990 to 2·9 years in 2021 for all sexes combined; this trend was particularly pronounced in males (from 3·2 years in 1990 to 3·9 years in 2021), whereas in females, the gap slightly narrowed (2·9 years to 2·6 years in females).
Acknowledgments
This work was done as part of GBD 2021, which was primarily funded by the Gates Foundation. SN is funded by Precursory Research for Embryonic Science and Technology from the Japan Science and Technology Agency (JPMJPR22R8) and the National Cancer Center Research and Development Fund (2024-A-14).
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Date accessed: July 1, 2024
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Lancet. 2020; 396:1160-1203
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