Occurrence and Risk Factors for Cognitive Decline Shared by Couples: A Systematic Review and Meta-Analysis

Background: To date, the magnitude of association and the quality of evidence for cognitive decline (mild cognitive impairment, Alzheimer's disease, and dementia) in couples and risk factors for outcomes have not been reviewed and analyzed systematically. Objective: The aim of this study was to investigate the concordance of cognitive impairment in unrelated spouses and to qualitatively describe potential risk factors. Methods: Eight databases were searched from inception to October 20, 2023. Eligible studies were independently screened and assessed for quality. Statistical analysis was conducted using Stata 15.1 software. The study was preregistered with PROSPERO (CRD42023488024). Results: Eleven studies involving couples were included, with moderate to high evidence quality. Compared to controls, spouses of individuals with cognitive impairment had lower cognitive scores (Cohen's d: 0.18-0.62) and higher risk of cognitive decline (OR = 1.42, 95% CI: 1.15-1.76). The consistency of cognitive impairment between spouses was attributed to three theories: 1) the impact of caregiving stress experienced by the spouse; 2) assortative mating, which suggests that individuals select partners with similar characteristics; and 3) the influence of shared living environments and lifestyles. Conclusions: The cognitive status of one spouse can affect the cognitive function of the other spouse. It is important to consider shared lifestyle, environmental, and psychobehavioral factors, as they may contribute to the risk of cognitive decline by couples. Identifying these factors can inform the development of targeted recommendations for interventions and preventive measures.