Sleep disturbance, physical frailty, and risk of cognitive impairment and dementia in older adults with subjective cognitive decline: a 10-year longitudinal study.

BACKGROUND: Subjective cognitive decline (SCD), a self-perceived decline in cognition without objective impairment, may represent an intermediate stage before clinical cognitive impairment develops. Sleep disturbance and physical frailty may reflect broader aging-related vulnerability and contribute to further cognitive progression in SCD. This study examined individual associations of sleep disturbance and physical frailty with 10-year incidence of cognitive impairment and dementia among older adults with SCD and explored whether physical frailty moderated the associations between sleep disturbance and cognitive outcomes.

METHODS: Data were drawn from 6 waves of the Health and Retirement Study (HRS; 2010-2020). Independent analyses of sleep included 3014 individuals with SCD at baseline, and frailty analyses used a subsample of 1141 with frailty data. Sleep disturbance was assessed using a modified Jenkins Sleep Scale, and physical prefrailty/frailty was defined by the Fried frailty phenotype. Incident cognitive impairment and dementia were identified using validated HRS cognitive cutoffs. Discrete-time survival models adjusted for socio-demographics and health-related covariates.

RESULTS: Sleep disturbance was not independently associated with incident cognitive impairment or dementia in fully adjusted models. Baseline physical prefrailty/frailty was significantly associated with increased odds of incident cognitive impairment (OR = 1.44, 95% CI: 1.15-1.80) and dementia (OR = 1.89, 95% CI: 1.23-2.93). Exploratory analyses suggested possible variation in the association between sleep disturbance and incident cognitive impairment by frailty status, but this finding should be interpreted cautiously.

CONCLUSIONS: Physical prefrailty/frailty is a significant factor of cognitive impairment in older adults with SCD, while the effect of sleep disturbance may vary by frailty status.