Prolonged loneliness and risk of incident cognitive decline and dementia: A two-cohort study.

BACKGROUND: Loneliness is prevalent currently and could result in increased dementia risks, whereas the associations of prolonged loneliness and its changes with cognitive decline and dementia remain less investigated.

METHODS: Data were from the English Longitudinal Study of Ageing (ELSA) and Health and Retirement Study (HRS). Loneliness was assessed using the Revised UCLA Loneliness Scale. Health risk factors for dementia included unhealthy lifestyles, depressive symptoms, chronic diseases, and functional limitations. Cognitive function was assessed using validated tests in both cohorts, with cognitive decline defined as cognitive z-scores < -1.5. Dementia was identified through self- or proxy-reported physician diagnoses. The Cox proportional hazard regression and Aalen's additive hazard regression were performed to calculate the relative and absolute risk for cognitive decline and dementia, respectively. Covariates including socio-demographic characteristics, social networks, and polygenic scores were adjusted.

RESULTS: Of 6721 ELSA and 10,195 HRS participants aged ≥50y, 2129 (13.7 %) and 612 (3.6 %) developed incident cognitive decline and dementia in about 10 years, respectively. Participants with severe (versus no) cumulative loneliness had 42 % and 98 % higher cognitive decline and dementia risks after pooling, corresponding to 791.6 (477.4-1105.8) and 372.8 (223.6-522.0) excess incidence densities (/10 person-years). Additionally, those who recovered from frequent loneliness (versus persistent frequent) were 9 %-31 % less likely to develop unhealthy lifestyles, depressive symptoms, chronic diseases, and functional limitations, and were at 33 % lower risks of dementia, corresponding to -248.6 (-446.0 ~ -51.2) excess incidence density.

CONCLUSIONS: Prolonged loneliness could increase the risks of incident cognitive decline and ADRD, while alleviating loneliness may help.