Population ageing and mortality during 1990-2017: A global decomposition analysis.

Background As the number of older people globally increases, health systems need to be reformed to meet the growing need for medical resources. A few previous studies reported varying health impacts of population ageing, but they focused only on limited countries and diseases. We comprehensively quantify the impact of population ageing on mortality for 195 countries/territories and 169 causes of death. Methods and findings Using data from the Global Burden of Disease Study 2017 (GBD 2017), this study derived the total number of deaths and population size for each year from 1990 to 2017. A decomposition method was used to attribute changes in total deaths to population growth, population ageing, and mortality change between 1990 and each subsequent year from 1991 through 2017, for 195 countries/territories and for countries grouped by World Bank economic development level. For countries with increases in deaths related to population ageing, we calculated the ratio of deaths attributed to mortality change to those attributed to population ageing. The proportion of people aged 65 years and older increased globally from 6.1% to 8.8%, and the number of global deaths increased by 9 million, between 1990 and 2017. Compared to 1990, 12 million additional global deaths in 2017 were associated with population ageing, corresponding to 27.9% of total global deaths. Population ageing was associated with increases in deaths in high-, upper-middle-, and lower-middle-income countries but not in low-income countries. The proportions of deaths attributed to population ageing in 195 countries/territories ranged from -43.9% to 117.4% for males and -30.1% to 153.5% for females. The 2 largest contributions of population ageing to disease-specific deaths globally between 1990 and 2017 were for ischemic heart disease (3.2 million) and stroke (2.2 million). Population ageing was related to increases in deaths in 152 countries for males and 159 countries for females, and decreases in deaths in 43 countries for males and 36 countries for females, between 1990 and 2017. The decreases in deaths attributed to mortality change from 1990 to 2017 were more than the increases in deaths related to population ageing for the whole world, as well as in 55.3% (84/152) of countries for males and 47.8% (76/159) of countries for females where population ageing was associated with increased death burden. As the GBD 2017 does not provide variances in the estimated death numbers, we were not able to quantify uncertainty in our attribution estimates. Conclusions In this study, we found that population ageing was associated with substantial changes in numbers of deaths between 1990 and 2017, but the attributed proportion of deaths varied widely across country income levels, countries, and causes of death. Specific preventive and therapeutic techniques should be implemented in different countries and territories to address the growing health needs related to population ageing, especially targeting the diseases associated with the largest increase in number of deaths in the elderly. Author summary Why was this study done? Evidence on the change in number deaths related to population ageing is important for each individual government to improve its healthcare system to address the increasing healthcare needs of older adults. Previous research assessing changes in health indicators (e.g., number of deaths, mortality) influenced by population ageing was limited to specific countries or specific diseases. Quantitative methods for decomposing changes in the total number of deaths that were adopted by previous studies are sensitive to the choice of the decomposition order of the 3 factors-population growth population ageing, and age-specific mortality rate-and the selection of reference group. What did the researchers do and find? Using a decomposition method that is not influenced by the selection of decomposition order of the 3 factors and the choice of the reference group, we conducted a comprehensive analysis to quantify the impact of population ageing on changes in the number of deaths in 195 countries/territories, and for 169 causes of death, from 1990 to 2017. Changes in the number of deaths related to population ageing varied greatly across the 195 countries/territories; the attributed proportion ranged from -43.9% to 117.4% for males and -30.1% to 153.5% for females. The causes of death for which population ageing was associated with the greatest increases in global deaths between 1990 and 2017 were ischemic heart disease (3.2 million) and stroke (2.2 million). The decreases in deaths attributed to mortality change exceeded the increases in deaths related to population ageing between 1990 and 2017 for the whole world, as well as in 55.3% (84/152) of countries for males and 47.8% (76/159) of countries for females where population ageing was associated with increased death burden. What do these findings mean? Globally, population ageing was related to increases in deaths, highlighting the importance and urgency of improving health systems to meet the health needs of older adults. Varying death burden related to population ageing suggests flexible health policies should target the leading causes of attributed death burden in different countries/territories. The death burden related to population ageing could be alleviated or even overcome through implementation of evidence-based interventions to reduce mortality.