Cognitive Decline Before and During COVID-19 Pandemic Among Older People With Multimorbidity: A Longitudinal Study

OBJECTIVE: To investigate whether older people living with multimorbidity would suffer an accelerated decline in cognition during the COVID-19 pandemic, compared with prepandemic data. DESIGN: A 5-year cohort conducting surveys from year 2016 to 2021, with 2016 to 2019 as the control period and 2019 to 2021 the pandemic period. SETTING AND PARTICIPANTS: In total, 9304 cognitively healthy older participants age ≥50 years were included from the Health and Retirement Study (HRS). METHODS: Multimorbidity was defined as the concurrent presence of 2 or more chronic diseases. A global cognition z score was calculated using memory (immediate and delayed word recall tests) and executive function (counting backwards and the serial sevens tests). Incident dementia was defined using either the reported physician diagnosis or an alternative approach based on cognition summary score. Linear mixed models were used to assess longitudinal changes, while modified Poisson regression models were used to analyze the risk of incident dementia. RESULTS: Of the 9304 participants included, 3649 (39.2%) were men, with a mean age of 65.8 ± 10.8 years. Participants with multimorbidity (n = 4375) suffered accelerated declines of 0.08 standard deviation (95% confidence interval 0.03, 0.13, P = .003) in global cognition and an elevated dementia risk (risk ratio 1.66, 95% confidence 1.05 to 2.61, P = .029), compared with individuals without morbidity (n = 1818) during the pandemic period. After further adjusting sociodemographic characteristics and prepandemic cognitive measurements, these differences remained evident. In contrast, no significant differences in cognitive declines were observed during the control period. CONCLUSIONS AND IMPLICATIONS: During the COVID-19 pandemic, older people with multimorbidity suffered an accelerated decline in cognition and elevated incident dementia risk, while no evident differences in cognitive decline rates were observed before the pandemic. Measures targeting vulnerable older people with multimorbidity could be significant for assisting these individuals to tackle neurocognitive challenges during the pandemic.