Multimorbidity and cognition among Canadian older adults: A three-decade perspective
Abstract
Background: Scarce information exists about whether the relationship between multimorbidity and cognitive decline has changed over the past decades.
Objectives: 1) To summarize knowledge about the association of multimorbidity and cognitive decline by performing a systematic review. 2) To estimate the association between multimorbidity in two cohorts selected three decades apart. 3)To identify which multimorbidity combinations have the strongest associations with cognitive decline 4) To identify protective factors that reduce the risk of cognitive decline in the presence of multimorbidity.
Methods: We performed a systematic review following the PRISMA statement. We then addressed objectives 2-4 by analyzing data from two longitudinal studies. The Canadian Study of Health and Aging (CSHA, n = 497) collected a baseline in 1991. The Canadian Longitudinal Study of Health and Aging (CLSA, n = 23654) had a baseline in 2015. Both studies collected information on several chronic conditions and used validated measures of different cognitive domains. Incident dementia was available in the CSHA only. Statistical models included multilevel linear and logistic regression and classification and regression trees (CART).
Results: We identified 19 publications evaluating the relationship between multimorbidity and cognitive decline, of which 17 studies reported statistically significant results for this association. We found no association between multimorbidity and cognitive scores in the CSHA, while in the CLSA, we found associations with frontal function (ß:–0.049) and RAVLT (ß:–0.05). We did not find an association between multimorbidity and 5-year dementia incidence in the CSHA. In the CLSA, CART identified cardiopathies and stroke as part of the multimorbidity combinations associated with the lowest cognitive test scores. Finally, in the CSHA, physical activity decreased dementia risk (OR = 0.45, 95% CI: 0.20–0.98).
Conclusion: Our systematic review supports the association between multimorbidity and cognitive decline without evidence of change over time. We found an association of multimorbidity on cognitive scores only in the ongoing CLSA; future research should clarify this apparent increasing effect of multimorbidity on cognition. We noticed that multimorbidity combinations containing cardiopathies and stroke were associated with low cognitive scores. Finally, we found that regular exercise reduced the risk of dementia in multimorbidity patients.