Background and Objective: Loneliness is common and its prevalence is rising. The relationship of loneliness with subsequent dementia and the early preclinical course of Alzheimer disease and related dementia (ADRD) remains unclear. Thus, the primary objective of this study was to determine the association of loneliness with 10-year all-cause dementia risk and early cognitive and neuroanatomic imaging markers of ADRD vulnerability.
Methods: Retrospective analysis of prospectively collected data from the population-based Framingham Study cohorts (09/09/1948-12/31/2018). Eligible participants had loneliness assessed and were dementia-free at baseline. Loneliness was recorded using the Center for Epidemiologic Studies Depression Scale; defined conservatively as feeling lonely ≥3 days in the past week. The main outcomes were incident dementia over a 10-year period, cognition, and MRI brain volumes and white-matter injury.
Results: Of 2308 participants (mean age, 73 [SD, 9] years; 56% women) who met eligibility in the dementia sample, 14% (329/2308) developed dementia; 6% (144/2308) were lonely. Lonely (versus not lonely) adults had higher 10-year dementia risk (age-, sex-, and education-adjusted hazard ratio, 1.54; 95% CI, 1.06-2.24). Lonely participants younger than age 80 without APOE ε4 alleles had a three-fold greater risk (adjusted hazard ratio, 3.03; 95% CI, 1.63-5.62). Among 1875 persons without dementia who met eligibility in the cognition sample (mean age, 62 [SD, 9] years; 54% women), loneliness associated with poorer executive function, lower total cerebral volume, and greater white-matter injury.
Discussion: Over 10 years of close clinical dementia surveillance in this cohort study, loneliness was associated with increased dementia risk; this tripled in adults whose baseline risk would otherwise be relatively low based on age and genetic risk, representing a majority of the US population. Loneliness was also associated with worse neurocognitive markers of ADRD vulnerability, suggesting an early pathogenic role. These findings may have important clinical and public health implications given observed loneliness trends.
Classification of Evidence: This study provides Class I evidence that loneliness increases the 10-year risk of developing dementia.