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

Abstract

Background: Traditional metrics for population health ageing tend not to differentiate between extending life expectancy and adding healthy years. A population ageing 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 ageing 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-standardised 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 analysed 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 ageing. We represent the uncertainty of our estimates by calculating uncertainty intervals (UI) from 1000 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 1000 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-standardised 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-standardised 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 ageing populations. Our findings could provide inputs into policymaking by identifying key drivers of variation in the ageing burden and resources required for addressing the burden.

Funding: National Institute on Aging of the National Institutes of Health.

Figure 1

Age-standardised rate and proportion of all health burden among the adult population that is age related, by SDI quintile (A) and GBD super-region (B) in 2017 All burden is shown split into age-standardised age-related burden (per thousand adults; dark bars) and age-standardised non-age-related burden (light bars). The percentages given represent the proportion of age-related burden among all burden. DALYs=disability-adjusted life-years. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study. SDI=Socio-demographic Index.

Figure 2

Comparing the equivalent ages to global average 65-year-olds across countries in 2017 The dashed line indicates global average 65-year-olds. Countries and territories are colour coded by their e. SDI=Socio-demographic Index.

Figure 3

Changes in age-standardised age-related burden rate between 1990 and 2017, by SDI (A) and GBD super-region (B) Percentage change between 1990 and 2017 is presented next to the arrows indicating direction of change. DALYs=disability-adjusted life-years. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study. SDI=Socio-demographic Index.

Figure 4

Decomposition of age-related burden between 1990 and 2017, by SDI (A) and GBD super-region (B) The dashed line marks net effect (zero change in DALYs from 1990). DALYs=disability-adjusted life-years. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study. SDI=Socio-demographic Index.

Figure 5

Comparison of age-standardised cumulative rates of age-related deaths in Mexico, Thailand, and the USA (A) and China, South Africa, and Saudi Arabia (B) and the frontier countries, with comparison of the scaled age-standardised cumulative rate of age-related deaths (C) Cumulative death rates in panel C are scaled to a range of 0 to 1, using country-specific cumulative death rate at age group 80–84 years (the highest observed life expectancy) as the reference point. The frontier countries are Switzerland (ages 25–64 years and 70–84 years), South Korea (65–69 years), Singapore (85–89 years), and Kuwait (90 years and older).