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Objectives Little research has explored how cognitive function and activities of daily living (ADL) affect each other over time. In addition, no current finding provides a clear hint to the temporal precedence between them. The present study tries to address these limitations of prior studies by utilizing a longitudinal data and advanced statistical modeling. Methods This study analyzed the data from the China Health and Retirement Longitudinal Study (CHARLS), a prospective observational study performed every 2 years for a total of three waves between 2011 and 2015 using a multistage probability sampling. Cognitive function was measured on the basis of three aspects of cognitive performance. Functional abilities were assessed using six types of activities of ADL and five types of instrumental ADL (IADL). Latent difference score modeling was employed to investigate the temporal precedence between cognitive function and ADL. Results The best fitting model indicates poor cognitive function precede worsening in ADL function, whereas the current findings did not support that poor ADL predate the cognition decline or reciprocal influence hypotheses. Conclusions The elderly with poor cognitive function may be more vulnerable to deterioration in ADL. Findings underscore the importance of early screening for cognitive function among the elderly as the key strategy to prevent further ADL impairment and keep independence.

Aim Cognitive impairment and functional deterioration are common in later life and often co‐occur with depressive symptoms (DS). This study aims to examine the individual effects and possible interaction between worsening cognitive function (CF) and deteriorating functional status (FS) on DS using large sample, longitudinal data. Methods Elderly people who completed the baseline survey of China Health and Retirement Longitudinal Study (CHARLS 2011) and the third wave survey (2015) were included. A multivariable logistic regression model was used to assess the individual effects. The relative excess risk due to interaction (RERI), the attributable proportion due to interaction (AP) and synergy index (SI) were calculated to evaluate the additive interaction. Results Worsening CF and deteriorating FS were associated with the increase in DS, while unchanged or improved CF and FS were associated with the decrease in DS. In addition, decreased (increased) FS led to more severe (improved) DS than decreased (increased) CF. The additive interaction between worsening CF and deteriorating FS on the increase in DS was significant. The estimates and 95% CI of the RERI, AP and SI were 0.626 (0.061, 1.190), 0.222 (0.042, 0.402) and 1.526 (1.016, 2.291) respectively. Conclusions Both worsening CF and deteriorating FS have positive interactions with the increase in DS. It is vital to focus on DS of elderly people with worsening CF and/or FS and to adopt interventions. Geriatr Gerontol Int 2020; 20: 343–347.

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