Loneliness and cognitive function in later life: a population-based counterfactual analysis.

BACKGROUND: Loneliness is increasingly recognized as a major public health challenge. Yet, its impact on cognitive function remains poorly understood. A complex interplay of life-course risk factors makes it challenging to disentangle the effect of loneliness from other factors and to assess underlying mechanisms when using traditional approaches.

METHODS: We applied the parametric g-formula with the Health and Retirement Study (1996-2018; n = 34 774; aged 50-80 years) to simulate an intervention estimating the effect of preventing loneliness on cognitive function. We assessed whether this effect varies by gender. Formal mediation analysis was also performed to assess depression as a potential pathway.

RESULTS: Preventing loneliness was protective against cognitive decline at all ages, with the magnitude increasing with age. Averaged across all ages, an intervention to prevent loneliness would slow cognitive decline by 0.075 points at the population level [95% confidence interval (CI): 0.063-0.089] and by 0.157 points among individuals experiencing loneliness (95% CI: 0.138-0.178). Overall, 17.3% of the total effect of preventing loneliness was mediated via depression, with the proportion mediated being 19.4% among men and 16.9% among women.

CONCLUSION: Employing an innovative counterfactual framework, this study shows that preventing loneliness could provide an insulative effect against cognitive decline, even at the population level. Importantly, with advancing age, addressing loneliness yields progressively greater cognitive benefits. The effects partly operate through reductions in depression, especially in men. Interventions against loneliness may help maintain cognitive function, with benefits extending to mental health, highlighting a promising avenue for public health strategies.