Associations of life course social determinants of health, social mobility with cognitive function and roles of social participation and lifestyle: a multicohort study

BACKGROUND: Social determinants of health (SDOH) throughout life are key factors affecting cognitive aging. The long-term effects of life course SDOH and social mobility on cognitive function are not well understood. We aimed to examine how stage-specific and cumulative SDOH and social mobility related to cognitive function and decline, considering the roles of lifestyle and social participation. METHODS: We pooled individual-level data (2010-2021) from three nationally representative longitudinal cohorts in the USA, China, and England. Ten SDOH indicators spanning four dimensions (education, financial circumstances, healthcare access, social context) across childhood, early adulthood, and middle-late adulthood were used to evaluate stage-specific and cumulative SDOH levels (high, medium, low). Twenty-seven social mobility patterns were identified based on life course SDOH transitions. Global and domain-specific (memory, executive function, orientation, verbal fluency) cognitive function were evaluated using Z-scores. Linear mixed-effects models were applied to investigate the associations of life course SDOH and social mobility with cognitive function and rate of decline. Mediation analyses evaluated the contributions of lifestyle and social participation to the link between SDOH levels and cognition. Combined effects of SDOH with lifestyle or social participation were also examined. RESULTS: Among 23,750 participants (mean age 63.5 years), medium (β - 0.319, 95% CI - 0.344 to - 0.293) and low (- 0.705, - 0.735 to - 0.676) cumulative SDOH were linked to poorer global and domain-specific cognitive function than high SDOH. Low cumulative SDOH predicted faster decline in global cognition (- 0.013 SD/year, - 0.019 to - 0.007), executive function (- 0.007 SD/year, - 0.012 to - 0.002), and orientation (- 0.019 SD/year, - 0.027 to - 0.011). Participants with persistently low SDOH exhibited the greatest decrease in global cognitive function (- 1.520, - 1.601 to - 1.439), while downward mobility accelerated cognitive decline (- 0.027 SD/year, - 0.040 to - 0.013). Lifestyles and social participation mediated 12.1% to 28.3% of the SDOH-cognition associations. At equivalent SDOH levels, unhealthy lifestyles and inactive social participation independently predicted poorer cognitive function. CONCLUSIONS: Lifelong social disadvantage and downward mobility were associated with lower cognitive function and faster decline. While promoting healthy lifestyles and social engagement may partly mitigate theses effects, comprehensive interventions addressing adverse SDOH across the lifespan are still important for reducing cognitive aging inequities.