Measuring population aging: an analysis of the Global Burden of Disease Study 2017

Abstract

Traditional metrics for population health aging tend not to differentiate between extending life expectancy and adding healthy years. A population aging metric that reflects both longevity and health status, incorporates a comprehensive range of diseases, and allows for comparisons across countries and time is required to understand the progression of aging and to inform policies.

Methods

Using the Global Burden of Diseases, Injuries, and Risk Factors Study 2017, we developed a metric that reflects age-related morbidity and mortality at the population level. First, we identified a set of age-related diseases, defined as diseases with incidence rates among the adult population increasing quadratically with age, and measured their age-related burden, defined as the sum of disability-adjusted life years (DALYs) of these diseases among adults. Second, we estimated age-standardized age-related health burden across 195 countries between 1990 and 2017. Using global average 65-year-olds as the reference population, we calculated the equivalent age in terms of age-related disease burden for all countries. Third, we analyzed how the changes in age-related burden during the study period relate to different factors with a decomposition analysis. Finally, we describe how countries with similar levels of overall age-related burden experience different onsets of aging. We represent the uncertainty of our estimates by calculating uncertainty intervals (UI) from 1,000 draw-level estimates for each disease, country, year, and age.

Findings

92 diseases were identified as age-related, accounting for 51.3% (95% UI 48.5–53.9) of all global burden among adults in 2017. Across the Socio-demographic Index (SDI), the rate of age-related burden ranged from 137.8 DALYs (128.9–148.3) per 1,000 adults in high SDI countries to 265.9 DALYs (251.0–280.1) in low SDI countries. The equivalent age to average 65-year-olds globally spanned from 76.1 years (75.6–76.7) in Japan to 45.6 years (42.6–48.2) in Papua New Guinea. Age-standardized age-related disease rates have decreased over time across all SDI levels and regions between 1990 and 2017, mainly due to decreases in age-related case fatality and disease severity. Even among countries with similar age-standardized death rates, large differences in the onset and patterns of accumulating age-related burden exist.

Interpretation

The new metric facilitates the shift from thinking not just about chronological age but the health status and disease severity of aging populations. Our findings could provide inputs into policymaking by identifying key drivers of variation in the aging burden and resources required for addressing the burden.