From chronic disease burden to cognitive decline: a systematic review of multimorbidity in older adults

Abstract Background Multimorbidity is common in older adults and has been associated with adverse cognitive outcomes. However, findings remain heterogeneous because of differences in multimorbidity definitions, cognitive measures, and study designs. This review aimed to synthesize evidence on the association between multimorbidity and cognitive outcomes in adults aged ≥ 60 years. Methods Following PRISMA 2020 guidelines, PubMed, Scopus, Web of Science, the Cochrane Library, and gray literature sources were searched up to August 2026. Observational studies examining multimorbidity, defined as ≥ 2 chronic conditions, and cognitive outcomes in adults aged ≥ 60 years were included. Methodological quality was assessed using Joanna Briggs Institute checklists, and findings were synthesized narratively. Results Seventeen studies met the eligibility criteria. Overall, greater multimorbidity burden was generally associated with poorer cognitive outcomes, while several specific multimorbidity patterns, particularly cardiometabolic and cardiovascular patterns, were associated with cognitive impairment, cognitive decline, or dementia. However, some studies reported null or domain-specific associations. Considerable heterogeneity was observed across multimorbidity definitions, cognitive assessments, study designs, populations, and confounding adjustment. Conclusion Multimorbidity may be associated with poorer cognitive outcomes in older adults, but the strength and consistency of the evidence vary across studies. Interpretation is limited by methodological heterogeneity, potential risk of bias, and the observational nature of the evidence. More standardized prospective studies are needed to clarify these associations.