Abstract
Background: Worldwide population ageing is motivating how to measure the health of ageing populations. One approach is to compare dynamics of frailty, assessed by the cumulative-deficit frailty index, across different populations. We aim to compare the frailty distribution, mortality risk, and change in frailty over time between 18 countries.
Methods: Using data from five harmonised international surveys (HRS, SHARE, ELSA, CHARLS and MHAS) we assessed frailty with a 40-item frailty index (baseline, 2-, 4- and 6-year follow-up), along with mortality status. We constructed separate regression models for participants with the fewest baseline health deficits (“zero-state” – assessing ambient health of the population) and the rest of the population (“non zero-state”). Using logistic and negative binomial, respectively, we assessed the odds of mortality and the rate of deficit accumulation (i.e. change in frailty index) between countries, adjusted for baseline frailty, age, and sex.
Results: Highest baseline frailty, mortality risk, and the most rapid increases in frailty were observed in Mexico, followed by China. Differences in mortality risk and deficit accumulation were similar regardless of baseline frailty. Lowest mortality risk and the slowest rates of deficit accumulation were observed in Scandinavian countries and in Switzerland. Differences between Central/Southern European countries, USA and UK varied when comparing zero-state with non zero-state models. For example, mortality rates and deficit accumulation were relatively lower among the healthiest subset of the USA (and to a lesser extent UK) population. However, when modelling those with some degree of baseline frailty, mortality and deficit accumulation in the USA were relatively higher compared to European countries.
Conclusion: Dynamics of the frailty index can provide insights into population-level differences in health across different settings. For some, but not all, countries, findings are sensitive to the degree of frailty present at baseline, which may reflect inequalities in healthcare provision or access.