The longitudinal path from happiness to cognitive performance: The role of loneliness and cognitive reserve

Purpose Happiness has been linked to better cognitive outcomes in older adults. Loneliness may serve as a mediator in this relationship, while cognitive reserve (CR) may buffer or enhance these effects. This study examined the direct effect of happiness on cognitive performance over two years, the mediating role of loneliness in this relationship, and whether CR moderates the direct and indirect (via loneliness) effects of happiness on cognitive performance. Methods Data were drawn from a longitudinal survey of adults aged 50 and above (N = 55,340). Cognitive performance was assessed at baseline (T1) and at a two-year follow-up (T2) using a composite score combining immediate recall, delayed recall, numeracy, and verbal fluency. Happiness was measured at T1 using a single-item scale, and loneliness was assessed via the short R-UCLA Loneliness Scale. CR was computed as a standardized composite of educational attainment, occupational complexity, and engagement in cognitive activities. Results Happiness at T1 significantly predicted better cognitive performance at T2 (B = 0.0098, p = .0197), and loneliness partially mediated this effect (indirect B = 0.002, 95% CI [0.001, 0.003]). CR moderated both the direct effect of happiness (interaction B = -0.0084, p = .0104) and the indirect effect via loneliness (interaction B = 0.0059, p = .0009), with stronger associations at lower levels of CR. Conclusion Happiness promotes cognitive health in later life, partly by reducing loneliness, especially among individuals with lower CR, highlighting the importance of emotional well-being and social connectedness in cognitively vulnerable populations.