BackgroundThe worldwide population ageing is a major driver for the increasing prevalence of multimorbidity, which is the co‐occurrence/ coexistence of multiple chronic conditions in the same individual. Simultaneously, cognitive decline has become a worldwide burden. Previous research has shown that there might be an association between multimorbidity as a risk for cognitive decline but no systematic review has evaluated this association.ObjectiveTo quantify the association between multimorbidity and cognitive decline through a systematic review, defining cognitive decline as a change in neuropsychological test scores or clinical diagnosis of mild cognitive impairment or dementia.MethodWe followed the PRISMA guidelines. We searched Medline/Pubmed, EMBASE, PsychINFO, CINAHL, LILACS, Scopus and ProQuest for studies published between January 1996 and May 2021. We evaluated study references for additional studies. We selected studies with a clear definition of multimorbidity, and cognitive decline, defined as cognitive impairment, dementia, or change in cognitive test scores. With one exception, all data were from high‐income countries and largely Caucasian populations. We employed the critical appraisal tools from the Joanna Briggs Institute to assess the risk of bias. We present a narrative data synthesis from each study in conjunction with key design information. PROSPERO register (CRD42020167253).ResultWe initially identified 1433 references, of which 16 studies fulfilled inclusion criteria, and were included; we found three additional studies through studies references. These studies encompassed a total of 90606 participants. Thirteen studies were cohorts, four cross‐sectional and two case‐control designs. Ten studies were population registers, five memory clinics cohorts, two population‐based surveys and one from administrative data. We found a high degree of heterogeneity among studies, driven by the use of multiple definitions of multimorbidity and cognitive decline that precluded a meta‐analysis. In general, all studies noticed an increased risk of cognitive decline or diminishing test scores with increasing accumulation of chronic disease. Future research will need to address a standardized definition of multimorbidity and cognitive decline/scores as well as obtain and evaluate data from low‐ and middle‐income countries.ConclusionWe found an association between suffering multimorbidity and increasing risk of cognitive decline measured as cognitive test scores or diagnosis of MCI or dementia.
BackgroundMultimorbidity is associated with cognitive decline. Little information exists regarding whether the relationship between multimorbidity and cognitive decline has changed over the last few decades.ObjectiveTo compare estimates of the association between multimorbidity (MM) and performance on cognitive tests in two prospective cohorts of Canadian community‐dwelling older adults recruited 24 years apart.MethodWe analyzed the two datasets separately, including participants ≥65 years from both baseline and first follow‐up of the Canadian Study of Health and Aging (CSHA, 1991 – 2001; first follow up in 1996) and the Canadian Longitudinal Study on Aging (CLSA, 2015 – ongoing; first follow up in 2018). We excluded participants with baseline dementia. In both cohorts, we defined MM as two or more conditions from a list of 14. The neuropsychological tests were Animal Naming Test (ANT) and the Rey Auditory Verbal Learning Test (RAVL) for both cohorts. Tests of frontal function were the Digit Symbol Substitution Test (DSST) in the CSHA and the Mental Alternation Task (MAT) in the CLSA. We performed multilevel linear modelling. We controlled for confounders, which were detected using a Directed Acyclic Graph.ResultWe included 497 participants from the CSHA and 9308 from the CLSA. The mean age was 78.0 in the CSHA and 72.0 in the CLSA, and male accounted for 36.4% in the CSHA and 50.2 in the CLSA. Mean MM was 2.1 in both cohorts, with a higher prevalence of MM in women (CSHA 63.9%; CLSA 64.2%) than in men (CSHA 55.8%; CLSA 59.5%). When comparing both cohorts, we found that baseline MM was not associated with changes in the Z‐scores for the ANT (CSHA: 0.16, CI95: ‐0.014 to 0.34; CLSA: ‐0.002, CI95: ‐0.044 to 0.04), RAVL delayed recall (CSHA ‐0.033, CI95: ‐0.23 to 0.16; CLSA: 0.031, IC95: ‐0.013 to 0.074), or DSST in CSHA (0.1, CI95: ‐0.084 to 0.29) / MAT in CLSA (0.008, CI95: ‐0.035 to 0.052).ConclusionWe did not find differences in Z‐scores changes over 5 years follow up in the CSHA and 3 years follow up in the CLSA, for three neuropsychological tests among Canadians ≥65 years recruited over two decades apart.
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