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

Healthier lifestyles are consistently 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. We harmonised data from six representative ageing cohorts spanning 32 countries. Cross-sectional analyses included 155,644 adults aged ≥ 50 years, and longitudinal analyses were conducted in 76,366 participants from five cohorts. A Healthy Lifestyle Score was constructed based on smoking status, alcohol consumption, physical activity and body mass index (BMI), and its association with the ATHLOS Healthy Ageing Index was examined. Using survey-weighted, within-country models, we estimated standardised predictive margins across lifestyle levels and quantified cross-national heterogeneity. Effect modification by country-level social determinants of health (SDOH) was assessed using random-effects meta-analysis and meta-regression. Across nearly all countries, healthier lifestyles were associated with higher health-ageing scores. However, the magnitude of these associations varied markedly. The difference in the Healthy Ageing Index between the healthiest and least healthy lifestyle levels ranged from 1.80 (95% CI: 1.40–2.19) in India to 8.12 (95% CI: 5.84–10.41) in Austria. Greater economic development, higher healthcare access and quality, stronger climate-adaptation capacity and broader urban infrastructure coverage were associated with larger lifestyle-related gains in healthy ageing. In contrast, income inequality, greater exposure to extreme climate events and a higher reliance on out-of-pocket health expenditure were linked to attenuated gains. Longitudinal joint modelling yielded consistent cumulative patterns over time. Together, these findings indicate that the health benefits of healthy lifestyles are not universally transferable and depend critically on social and environmental contexts, underscoring the need to integrate individual-level lifestyle interventions with structural policies to promote equitable healthy ageing.