Joint changes in subjective memory and objective cognition and risk of incident functional dependence: A harmonized analysis of four aging cohorts.

INTRODUCTION: The prognostic value of concurrent changes in subjective memory and objective cognition for later functional dependence remains unclear across populations.

METHODS: We conducted a harmonized multicohort longitudinal analysis of the China Health and Retirement Longitudinal Study (CHARLS), US Health and Retirement Study (HRS), English Longitudinal Study of Ageing (ELSA), and Survey of Health, Ageing and Retirement in Europe (SHARE). Subjective memory and objective cognition were assessed at baseline (T0) and first follow-up (T1). Participants were classified into four trajectory groups, and incident functional dependence after T1 was examined using cohort-specific Cox models and pooled random-effects meta-analysis. Sensitivity analyses addressed alternative decline thresholds, continuous change-score models, fixed follow-up windows, baseline-level adjustment, multiple imputation, and competing-risk models treating death as a competing event in cohorts with adequate mortality information.

RESULTS: Among 86,562 participants included in trajectory derivation and 62,329 included in fully adjusted outcome analyses, concordant decline showed the strongest and most consistent association with incident functional dependence. In pooled Cox analyses, concordant decline was associated with the greatest risk increase (hazard ratio [HR] 1.470, 95% confidence interval [CI] 1.381-1.566), with smaller associations observed for subjective-only decline (HR 1.222, 95% CI 1.055-1.415) and objective-only decline (HR 1.116, 95% CI 1.038-1.200). In competing-risk analyses across CHARLS, HRS, and SHARE, concordant decline remained the strongest association after accounting for death (pooled subdistribution HR 1.386, 95% CI 1.273-1.509).

DISCUSSION: Joint cognitive change, especially concordant decline, may improve identification of older adults at risk of future functional dependence.