Unequal health returns of healthy lifestyles across countries: the role of social and environmental contexts in healthy ageing

Abstract Background Healthier lifestyles are associated with better healthy ageing, yet whether these benefits are comparable across countries, and to what extent they depend on broader social and environmental contexts, remains poorly understood. Methods We harmonised data from six representative ageing cohorts spanning 32 countries. Longitudinal analyses were conducted in 76,366 participants from five cohorts, and cross-sectional analyses included 155,644 adults aged 50 years or older. We constructed a four-component healthy lifestyle score (HLS-4) based on smoking status, alcohol consumption, physical activity, and body mass index (BMI), and examined its association with the ATHLOS Healthy Ageing Index (HAI). Using survey-weighted country-specific models, we estimated standardised predictive differences across lifestyle levels and quantified between-country heterogeneity. Effect modification by country-level social determinants of health (SDOH) was assessed using random-effects meta-analysis and meta-regression. Results Across nearly all countries, healthier lifestyles were associated with higher healthy-ageing scores, but the magnitude of these associations varied substantially. Under the primary model adjusted for age, biological sex, living region, education, wealth, and marital status, the HAI difference between the healthiest and least healthy lifestyle levels ranged from 1.57 (95% CI: 1.18–1.97) in India to 7.24 (95% CI: 5.23–9.26) in Austria; estimates were slightly attenuated after additional adjustment for chronic disease burden. Indicators reflecting greater economic development, higher healthcare access and quality, stronger climate-adaptation capacity, and broader urban infrastructure coverage showed positive effect modification of the HLS-4 and healthy-ageing association, whereas income inequality, greater exposure to extreme climate events, and higher reliance on out-of-pocket health expenditure showed negative effect modification. Longitudinal joint modelling yielded directionally consistent cumulative patterns over time. Conclusions Findings suggest that health returns associated with healthy lifestyles are not universally equivalent across countries, and that structural factors may modify the extent to which individual lifestyle patterns translate into healthy ageing.