Association between multimorbidity trajectories and subsequent cognitive decline: evidence from two nationwide longitudinal cohorts.

BACKGROUND: The number of chronic diseases in a patient may change over time, but how multimorbidity developmental trajectories affect subsequent cognitive decline remains unknown.

METHODS: Data were drawn from eight waves (2004-2018) of the English Longitudinal Study of Ageing (ELSA) and the Health and Retirement Study (HRS), involving 5300 and 4357 participants, respectively. Group-based trajectory modeling was used to identify multimorbidity trajectories over six years (2004-2010) according to ten chronic diseases. We performed linear mixed-effects models to investigate the association between multimorbidity trajectories and subsequent cognitive decline in global cognition and three cognitive domains, including memory, executive function, and orientation.

RESULTS: Three multimorbidity trajectories (low-stable, moderate-increasing, and rapid-increasing) were identified in two cohorts. Compared to the low-stable trajectory group, the moderate-increasing trajectory group exhibited faster declines in memory [pooled β = -0.027 standard deviation (SD)/year, 95 % confidence interval (CI): -0.044 to -0.011], orientation (pooled β = -0.036 SD/year, 95 % CI: -0.066 to -0.006), and global cognition (pooled β = -0.043 SD/year, 95 % CI: -0.084 to -0.002). Furthermore, the rapid-increasing trajectory group was associated with steeper declines in memory (pooled β = -0.049 SD/year, 95 % CI: -0.084 to -0.015), executive function (pooled β = -0.044 SD/year, 95 % CI: -0.065 to -0.022), orientation (pooled β = -0.077 SD/year, 95 % CI: -0.116 to -0.037), and global cognition (pooled β = -0.138 SD/year, 95 % CI: -0.211 to -0.065).

LIMITATIONS: Limited by the structure of questionnaire, some of the information was derived by self-report, which may lead to recalling bias.

CONCLUSIONS: Both moderately and rapidly increased multimorbidity are associated with accelerated cognitive decline among older people. Multimorbidity surveillance and management might help to delay the decline rate of cognition.