Background:
Multimorbidity is associated with greater disability and accelerated declines in physical functioning over time in older adults. However, less is known about its effect on cognitive decline.
Methods:
Participants without dementia from the Health and Retirement Study were interviewed about physician-diagnosed conditions, from which their multimorbidity-weighted index (MWI) that weights diseases to physical functioning was computed. We used linear mixed-effects models to examine the predictor MWI with the modified Telephone Interview for Cognitive Status (TICSm, global cognition), 10-word immediate recall and delayed recall, and serial 7s outcomes biennially after adjusting for baseline cognition and covariates.
Results:
Fourteen thousand two hundred sixty-five participants, 60% female, contributed 73,700 observations. Participants had a mean ± SD age 67 ± 9.3 years and MWI 4.4 ± 3.9 at baseline. Each point increase in MWI was associated with declines in global cognition (0.04, 95% CI: 0.03-0.04 TICSm), immediate recall (0.01, 95% CI: 0.01-0.02 words), delayed recall (0.01, 95% CI: 0.01-0.02 words), and working memory (0.01, 95% CI: 0.01-0.02 serial 7s; all p < .001). Multimorbidity was associated with faster declines in global cognition (0.003 points/year faster, 95% CI: 0.002-0.004), immediate recall (0.001 words/year faster, 95% CI: 0.001-0.002), and working memory (0.006 incorrect serial 7s/year faster, 95% CI: 0.004-0.009; all p < .001), but not delayed recall compared with premorbid slopes.
Conclusions:
Multimorbidity using a validated index weighted to physical functioning was associated with acute decline in cognition and accelerated and persistent cognitive decline over 14 years. This study supports an ongoing geriatric syndrome of coexisting physical and cognitive impairment in adults with multimorbidity. Clinicians should monitor and address both domains in older multimorbid adults.