Social Isolation, Loneliness, and Accelerated Aging: A Multidimensional Approach Towards Aging

Background/Objectives: Approximately 24% of US older adults experience social isolation, while 43% of those over 60 reports feeling lonely. The health risks of social isolation and loneliness (SI/L) are significant, comparable to smoking 15 cigarettes a day and potentially shortening one’s life by 15 years. However, the biopsychological mechanisms by which SI/L are associated with health outcomes are understudied. Furthermore, it’s unclear how the variability of SI/L (i.e., continuation vs. recovery) may contribute to the aging process. This dissertation aims to model the patterns and joint trajectories of SI/L and examine the biological mechanisms through which they impact accelerated aging. Methods: The study used data from a nationally-representative longitudinal dataset, the US Health and Retirement Study (HRS) 2006-2020, which included 12,709 participants aged 50 and older. Social isolation was measured by the Steptoe’s Social Isolation Index, while loneliness was measured by the 3-item UCLA Loneliness scale. Biological aging was assessed through DNA methylation-based measures (PhenoAge, GrimAge, and DunedinPoAm) from the HRS Venous Blood Study 2016. Functional aging included measures of physical function, cognitive function, and motoric cognitive risk syndrome. Statistical methods included Cox proportional hazard model, group-based joint trajectory model, and causal mediation model. Results: The findings revealed that chronic loneliness, compared to transient or no loneliness, was associated with a higher risk of functional disability in middle-aged and older adults, especially women (Manuscript 1). Five distinct trajectories of SI/L were identified. The largely unparallel changes of SI/L over time and their separate and joint contributions to accelerated biological aging provide support for the need to treat them differently. Persistently isolated/moderately lonely older adults had the highest biological aging acceleration (PhenoAge, GrimAge, and DunedinPoAm) compared to those who were rarely isolated/rarely lonely (Manuscript 2). Causal mediation analysis found that biological age acceleration mediated 6.7-11.8% in the effect of social isolation on subjective cognitive complaint, slow gait, and motoric cognitive risk syndrome. (Manuscript 3). Conclusions: The findings indicated that strategies for addressing SI/L could prevent chronic diseases and functional decline via slowing biological aging. The study provides new knowledge by identifying SI/L as the proximate determinants of deficits in healthy aging and informs public health practice and policy advancement by identifying sensitive biological measures and optimal time points for evaluating interventions and supporting healthy aging and longevity.