Social isolation, loneliness, and their joint effects on cognitive decline and incident Alzheimer's disease: Findings from the Chicago health and aging project.

backgroundThere has been contradictory evidence on the prospective associations between social isolation/loneliness (SI/L) and cognitive decline (CD). There is also a scarcity of large and diverse population-based cohort studies examining SI/L that have confirmed clinical diagnoses of Alzheimer's Disease (AD). Notably, beyond individual associations, whether the effects of SI/L compound and accelerate CD and incident AD are not known.

objectivesWe hypothesized that SI and L, independently, would be associated with CD and incident AD to a similar extent, and the association of SI with CD and incident AD would be higher in lonely older adults.

designProspective cohort study.

settingUrban Chicago areas.

participantsWe analyzed data in the Chicago Health and Aging Project (CHAP), which comprised 7,760 biracial community-dwelling older adults [mean age (standard deviation (SD))=72.3 (6.3); 64 % Black & 63 % women; mean (SD) of follow-up=7.9 (4.3) years]. INTERVENTION (IF ANY): NA MEASUREMENTS: Linear mixed and logistic regression models were used to regress CD and incident AD separately on the SI index/L.

resultsSI index and L were significantly associated with CD, with one-point increase of beta estimate (SE, p-value) = -0.002 (0.001,0.022) and -0.012 (0.003,<0.001), respectively. Given that the SI index ranges from 0 to 5 and the L from 0 to 1, they had similar effect sizes. Similarly, there were significant associations between SI index and incident AD, odds ratio (95 % CI, p-value) = 1.183 (1.016-1.379,0.029), and between L and incident AD, 2.117 (1.227-3.655,0.006). When stratified by loneliness status, compared to older adults who were not isolated and not lonely, older adults who reported being socially isolated and not lonely experienced accelerated CD, -0.003 (0.001,0.004), despite no significantly increased odds of incident AD.

conclusionsSI/L had significant associations with CD and incident AD. Notably, socially isolated older adults who reported not being lonely appeared to be most socially vulnerable to CD. These findings suggest a specific at-risk subgroup of socially vulnerable older adults for future targeted interventions to improve cognitive health.