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

Abstract

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.

Keywords

Alzheimer’s disease cognitive decline dementia meta-analysis risk factor spouses concordance systematic review

INTRODUCTION

Dementia currently affects around 50 million individuals globally, with projections suggesting a threefold increase by 2050 [1]. Cognitive impairment covers a range of cognitive deficits resulting from various causes, impacting specific cognitive areas such as orientation, memory, calculation, attention, language, executive function, reasoning, and visuospatial abilities [2]. This condition can have a significant impact on social functioning and quality of life, with severe cases potentially leading to fatality. Cognitive impairment is classified by severity as either mild cognitive impairment (MCI) or dementia, with MCI often acting as a transitional phase between normal aging and Alzheimer’s disease (AD) [3]. Recognized as an early sign of AD, MCI involves a decline in cognitive abilities developed over time [3]. Early detection of MCI allows for timely intervention to address potential complications related to cognitive decline.

Numerous studies have indicated that couples tend to exhibit similar health statuses. Research has shown that cognitive function can be alike among partners [4 –6], and cognitive impairment in one spouse is a significant independent risk factor for cognitive decline [7, 8]. Furthermore, spouses of individuals with cognitive impairment face a heightened risk of decline in various cognitive domains such as general cognition, executive function, memory, and language [9]. Within families, there may exist ‘social’ clusters of diseases alongside ‘biological’ (i.e., genetic) clusters, as evidenced by the concordance of health outcomes between partners. Despite often lacking genetic relatedness, spouses may share common living environments, resources, social habits, dietary patterns, physical activity levels, and other health behaviors [5, 10]. This shared risk may stem from the adoption of common habits post-marriage or from initial similarities in behavior due to non-random or assortative mating. Given the shared environments, lifestyles, and consistent physical and mental health factors between partners, these common risk factors could contribute to the cognitive decline observed in couples [11 –13].

Several studies have reported cognitive decline and potential risk factors in couples, but these findings are often limited to specific countries. This study aims to conduct a systematic review and meta-analysis to investigate whether the cognitive status of one spouse impacts the cognitive function of the other, identify risk factors contributing to cognitive decline in couples, and summarize relevant research findings. Recent research on dementia prevention, intervention, and care suggests that a significant portion of dementia cases could be prevented by targeting modifiable risk factors. This study offers a more in-depth and specific examination of risk factors for cognitive decline within couples at the family level, potentially informing more effective screening strategies and improved prevention and management programs by promoting health behavior change through collaborative efforts between partners.

METHODS

Our systematic review was conducted following the established guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [14]. The protocol for this review has been registered and documented in the International Prospective Register of Systematic Reviews (PROSPERO) under the protocol number CRD42023488024. No patient informed consent was required.

Search strategy

We conducted an extensive search of electronic databases, including CNKI, Wanfang, VIP, PubMed, Web of Science, CINAHL, the Cochrane Library, and Embase, spanning from the inception of these databases up until 20 October 2023. Our search strategy utilized subject headings and keywords, such as ‘cognitive impairment’, ‘cognition disorders’, ‘mild cognitive impairment’, ‘spouse’, ‘couple’, ‘partner’, ‘wife’, ‘husband’, ‘married’, and ‘risk factors’, ‘factor’, ‘influence factors’, ‘correlates’. The search was conducted by two investigators, and the detailed strategy is shown in the Supplementary Material. Additionally, we performed a manual examination of the reference lists of identified studies to identify any additional potentially relevant publications through citation tracking. Data management was facilitated using Endnote, and the screening process involved independent evaluation of titles and/or abstracts of studies retrieved from the systematic literature search and other sources by two reviewers to identify potentially eligible studies.

Inclusion and exclusion criteria

Study eligibility was meticulously determined by two independent researchers, with any discrepancies resolved through consensus by a third reviewer. The inclusion criteria for this study were as follows: 1) The participants consisted of long-standing married couples residing together; 2) The primary outcome measure focused on the cognitive function of the couples; 3) The control group comprised spouses exhibiting normal cognitive function. Conversely, the exclusion criteria encompassed the following aspects: 1) Inability to access the full text of the study; 2) Repetition of literature, reviews, or case reports; 3) Whether the caregiver was the spouse of the person with cognitive impairment was not reported; 4) Insufficient or unobtainable data within the original research.

Screening and data extraction

Data extraction was undertaken independently by two authors (MHY and LJR). Discrepancies, if any, were meticulously identified and effectively resolved through comprehensive discussions and ultimately by a third reviewer (ZJX). Studies were reviewed initially on the basis of title and abstract, and then full text were reviewed for those deemed relevant studies. Data were abstracted in duplicate (by MHY and LJR) from ultimately included studies. For the purpose of this review, cognitive impairment was defined as mild cognitive impairment or dementia. The extracted information comprised a comprehensive array of key elements, including:

Thorough documentation of the study particulars, encompassing essential details such as the first author, year of publication, country of origin, source population, age restrictions, study design, and analytical sample size.

Comprehensive exploration of the cognitive decline assessment tools employed, coupled with an exhaustive evaluation of potential risk factors. These encompassed diverse domains, ranging from demographic factors, physical inactivity, socioeconomic status, and health status, to mental health and cardiovascular risk factors, among others.

Identification of primary outcome measure(s), serving as pivotal focal points for the study’s objectives.

Succinct yet informative summaries were meticulously crafted to offer a comprehensive overview of the study’s findings.

Quality assessment

The quality assessment of the included studies was conducted meticulously by two authors (MHY and LJR), with any discrepancies being discussed and resolved through consultation with a third reviewer (ZJX). Case-control or cohort studies were assessed using the widely recognized Newcastle– Ottawa Scale (NOS) [15], which incorporates crucial aspects such as study population selection, comparability, and outcome assessment. A maximum score of 9 points can be achieved, indicating high quality, with a total score of ≥6 considered indicative of high quality. For cross-sectional studies, the bias risk evaluation standard recommended by the Agency for Healthcare Research and Quality (AHRQ) [14, 16] was utilized. This standard comprises 11 scoring items, with responses categorized as “yes,” “no,” or “unclear” based on the content of each item. The results were compiled and presented using the Cochrane assessment tool, with responses replaced by “low risk,” “high risk,” or “unclear risk.” This rigorous quality assessment process ensures the reliability and credibility of the included studies in this review.

Data synthesis and analysis

The data synthesis and analysis were performed using Stata 15.1 software, employing robust statistical methods to examine the cognitive impairment in couples. Cohen’s d value and its corresponding confidence interval were utilized to estimate the differences in cognitive function between the two groups, one with cognitive impairment and the other without. To represent the effect size of the risk of cognitive impairment in these groups, odds ratios (OR) with their respective 95% confidence intervals were employed. Statistical heterogeneity was assessed using I square (I ²) values, where an I ² greater than 50% indicated significant heterogeneity, leading to the utilization of a random effects model for calculating the pooled effect size. Conversely, a fixed effects model was employed when the I ² value was below 50%. In cases where data extraction or synthesis was not feasible from the original articles or when risk factors were reported in only one study, a descriptive approach was employed to present the results. Descriptive analysis was employed due to the limited number of studies available for each risk factor and the considerable differences in influencing factors across the studies. Publication bias was assessed using Egger’s test, providing insights into the potential bias in the reported findings.

RESULTS

Literature search process and results

The literature search process yielded a total of 821 relevant articles from each database. After removing 70 duplicate articles, the remaining articles underwent a thorough screening process, which involved reviewing the titles, abstracts, and full texts. Following this screening process, 11 studies met the inclusion criteria and were selected for further analysis (see Fig. 1).

Fig. 1

Selection strategy and results.

Literature basic characteristics and quality evaluation

The included studies in this review consisted of six studies that examined the comparison of cognitive scores between elderly individuals whose spouses had dementia (DCG) and those whose spouses did not have dementia (NCG). These six studies encompassed a total of 687 cases in the DCG group and 1628 cases in the NCG group. Additionally, three studies focused on assessing cognitive function in couples, involving a total of 5,071 couples. The overall sample size across all included studies comprised 12,457 elderly individuals. The study locations encompassed the United States, Netherlands, and Korea. One study specifically explored the perceptions of patients with mild cognitive impairment and their spouses regarding the content validity, practicality, and acceptability of the Enhanced Meaningful Activities of Daily (DEMA) program. Another evaluation article was included as it examined other potential risk factors for cognitive decline shared by couples. The reported outcomes of cognitive impairment in all studies primarily included mild cognitive impairment and dementia.

In our included studies, there were variations in the assessment of cognitive functioning as the primary outcome measure. These assessments included clinical examinations conducted by geriatric neurologists and/or neuropsychologists, telephone interviews, and questionnaires. Additionally, different assessment tools were chosen, but they generally covered various aspects of cognitive functioning, such as memory, attention, orientation, and language executive functions. During clinical examinations, geriatric neurologists and/or neuropsychologists may employ a range of cognitive tests to evaluate individuals’ cognitive status. These tests may include assessments of memory, such as the ability to recall words or images; attention tests, such as sequence recall or abstract reasoning; orientation tests, involving awareness of time, place, and current events; and language executive function tests, such as vocabulary and grammar comprehension. Telephone interviews and questionnaires provide a more convenient way to assess individuals’ cognitive functioning. By asking questions about memory, attention, language abilities, and other aspects of daily life, researchers can gain preliminary insights into individuals’ cognitive functioning. Although there may be variations in assessment methods and tools, the overall aim of the selected evaluation tools was to comprehensively assess different aspects of cognitive functioning. This helps us gain a better understanding of the relationship between cognitive decline and risk factors. Study characteristics and spousal association effect estimates are shown in Table 1.

Table 1

The basic characteristics and association effect estimates of included study

AuthorYear	Study design	Country	Cognitive Decline assessment tools	Samples N;Age[Mean (SD)]	Scores/ prevalence; number (%)effects sizes(Cohen’s d/OR/HR)	Relevant mediators or risk factors	Sco-res
Caswell 2003 [17]	CC	USA	DST (information processing speed, attention, and concentration)	DCG (PWD spouses) 44; 74.27(7.91)NCG 6670.85 (6.32)	DCG had lower DST scoresd = – 0.62(– 1.01, – 0.23)	Caregiver psychological distress (uplifts, burden, and sleep problems).	6
Vugt 2006 [18]	Cohort studiesF/U 1 year	Netherlands	MMSE (global cognitive functioning)	DCG (PWD spouses) 5468.4 (8.5)NCG 10868.3 (8.4)	DCGs performed worse on global cognitive functiond = – 0.42(– 0.75, – 0.09)F/U: not provided	Low performance on a verbal memory task was related to SCD+subjective competence and psychological complaints, as well as CD+hyperactivity and dementia severity.	6
Vitaliano 2005 [19]	cohort studiesF/U 2 years	USA	SILS (vocabulary and abstraction)	DGG (PWD spouse) 9672.2 (9.3)NCG 9571.0 (6.9)	Groups similar at baseline.F/U: DCG had lower SILS score, d = – 0.16 (– 0.439, 0.129).DCG declined by 1 point relative to NCG (0.01 points)	Hostile attribution and metabolic risk mediated SCD+cognitive decline.	8
Vitaliano 2009 [20]	cohort studiesF/U 2 years	USA	DST (processing speed, complex attention psychomotor speed, cognitive motor translation, and concentration)	DGG (PWD spouse) 12271.7 (8.9)NCG 11770.2 (7.2)	DCG had lower DST scores, d = – 0.29 (– 0.55, – 0.04)F/U: DCGs had lower DST score, d = – 0.38(– 0.64, – 0.13)	greater psychological complaints (depression and anxiety) predicted DST decline and mediated greater DST decline in SCD+.	7
Pertl 2015 [21]	cohort studies	USA	WJ-III (Separate reasoning and vocabulary scores)	DCG (PWD spouse) 17973.49 (11.16)NCG 17972.16 (11.11)	DCGs deficits on Vocabulary, d = – 0.18(– 0.39, 0.03)	Men, low-income and psychological complaints (depression and anxiety) individuals who have a spouse with dementia are more likely to contribute to cognitive decline.	8
Dassel 2015 [22]	cohort studiesF/u: 4 years	USA	mTICS (episodic memory, working memory, processing speed)	DCG (PWD spouse) 19276.41 (8.93)NondementiaCG (1063)72.38 (9.67)	Cognitive scores at baseline and follow-up did not differ between the two groups. But DCGs declined by 1.77 points relative to NCG (0.87 points)	DCG cognition score (at study entry).	6
Norton 2010 [23]	cohort studiesF/u: 12.6 years	USA (northern Utah)	MMSE (global cognitive functioning)IQCODE, CA	SCD⁺ 22975.7 (5.9)SCD^- 221373.1 (5.3)	34 (14.8)221 (10.0)HR 6.01 (2.23, 16.17)	Spouses who were older, lower couple-level socioeconomic status (SES), and had one or more APOE ɛ4 alleles were more likely to have dementia events.	5
Yang 2021 [24]	cohort studies	Korean	CERAD-NP (memory, physical and neurologic examinations)	SCD⁺ 12175.7 (6.0)SCD^- 66373.2 (6.1)	47 (38.8)150 (22.6)OR 1.74 (1.12, 2.69)	Risk factors shared within couples: physical inactivity, history of head injury, major depressive disorder.	7
Lee 2023 [25]	cohort studiesF/u: 8 years	USA	10 Cognitive Assessments(memory, language/ executive function, and processing speed)	SCD⁺ 50775.7 (4.8)SCD^- 133874.5 (4.4)	49 (9.6)110 (8.2)b = 0.09 (0.18, 0.00)HR 0.97 (0.69, 1.38)	Shared risk factors present in mid-life couples: educational attainment, smoking, alcohol consumption, physical activity, BMI, hypertension.	7
Vitaliano 2021 [26]	Comment	NR	NR	NR	NR	Assortative mating, dyadic lifestyles, and caregivers chronic stress.	NR
Lu 2011 [27]	Qualitative interview study	USA	Clinical examination by the geriatric neurologist and/or neuropsychologist	SCD⁺ 9SCD^- 9	NR	NR	NR

CC, case-control; CS, cross-sectional; F/u, follow-up; DCG, dementia caregivers; NCG, non-caregivers; PWD, person with dementia; CD⁺, participants with cognitive impairment; CD-, participants without cognitive impairment; SCD+, spouses of CD⁺ participants; SCD^–, spouses of CD^– participants; Tools: DST, Digit-Symbol Test; MMSE, Mini-Mental State Exam; SILS, Shipley Institute of Living Scale; WJ-III, Woodcock Johnson III test battery; mTICS, modified Telephone Interview for Cognitive Status; IQCODE, Informant Questionnaire for Cognitive Disorder in Elderly; CA, in-depth clinical assessment; CERAD-NP, Consortium to Establish a Registry for Alzheimer Disease Neuropsychological Assessment Battery; 10 Cognitive Assessments, Digit Symbol Substitution, Delayed Word Recall, Phonemic Fluency, Logical Memory, Digit Span, incidental learning, Trail Making parts A and B, phonemic fluency, and the Boston naming test.

Among the 11 included articles, seven were cohort studies, and one was a case-control study. The quality of cohort and case-control studies was assessed using the Newcastle-Ottawa Scale (NOS) criteria [14], with one article being of moderate quality and eight articles being of high quality according to the evaluation results. The quality of the cross-sectional studies was evaluated according to the Agency for Healthcare Research and Quality (ARHQ) criteria, which indicated moderate quality. Additionally, the included studies comprised one review and one qualitative study, both of which did not undergo a formal quality evaluation.

Occurrence of shared cognitive decline in couples

Cognitive decline was more rapid in spouses of patients with cognitive impairment.

The results of the analysis of baseline data, as depicted in Table 1, revealed that spouses of patients with cognitive impairment (DCG) exhibited worse cognitive function, particularly in vocabulary performance, compared to age-matched controls. The effect sizes (Cohen’s d) ranged from 0.18 to 0.62 across the five studies, suggesting small to moderate effects. The heterogeneity test showed an I ² value of 27.2%. A fixed effects model was employed for the meta-analysis, yielding an overall effect size (Cohen’s d) of –0.35 (–0.46, –0.23), indicating a moderate effect (see Fig. 2). However, one study did not demonstrate a significant difference between groups at baseline and was therefore not included in the meta-analysis [19].

Fig. 2

Forest plot of meta-analysis of cognitive function between spouses of patients with cognitive impairment and spouses of controls.

Regarding cognitive scores after follow-up, two studies [19, 20] reported lower scores in the DCG group compared to the NCG group, with Cohen’s d values of –0.16 and –0.38, respectively. These findings indicate that DCG experiences a greater degree of cognitive decline than NCG individuals of the same age. In the study by Vitaliano et al. [19], DCG showed a decrease of 1 point (0.01 points) relative to NCG, with a statistically significant difference. Similarly, Dassel et al. [22] found that DCG exhibited a decrease of 1.77 points (0.87 points) compared to NCG.

The risk of cognitive impairment is higher in spouses with cognitive impairment

Within the scope of our analysis, we included three studies that specifically examined the prevalence of cognitive impairment in couples. The findings consistently indicated that the risk of cognitive impairment was higher in spouses with cognitive impairment (SCD+) compared to spouses without cognitive impairment (SCD-). In total, 5071 couples were evaluated across the three studies, with 857 spouses classified as SCD+ and 4214 spouses classified as SCD-. The assessment of heterogeneity among the studies revealed no significant variation (I ² = 5.6%). Consequently, a fixed effects model was employed for the meta-analysis. The results of the meta-analysis demonstrated a statistically significant difference in the prevalence of cognitive impairment between the two groups (see Fig. 3), with an odds ratio (OR) of 1.42 and a 95% confidence interval (CI) ranging from 1.15 to 1.76 (P-value = 0.001).

Fig. 3

Forest plot of cognitive impairment in spouses and risk of developing cognitive impairment.

Risk factors for cognitive decline in elderly couples

In terms of spouses acting as caregivers with cognitive impairment, several studies have highlighted that caregivers of individuals with cognitive impairment exhibit significant cognitive deficits compared to non-caregiving spouses (NCG). Apart from age and education level, caregiving status [17 –22] has been identified as a predictor of cognitive scores or changes in scores. This association may be influenced by the composite effects of distress rather than solely by depression. Two studies [20, 21] have indicated that this association is mediated by psychological complaints such as anxiety and depression, and that the subjective competence of caregivers is linked to cognitive impairment [18]. However, in Vitaliano et al.’s study [19], the association was mediated by hostile attribution and metabolic risk. Pertl et al.’s findings suggest that caregivers, particularly men, and individuals with lower incomes are more likely to experience adverse cognitive outcomes [21]. In addition to older age, lower socioeconomic status, and possessing the APOE ɛ4 allele, cognitive impairment in the spouse has been identified as an independent risk factor for cognitive impairment, with gender acting as a moderator [23].

In terms of people with cognitive impairment, the current study reveals that certain characteristics, such as the severity of dementia and presence of behavioral symptoms like hyperactivity, increase the risk of developing cognitive impairment in caregivers [18].

One study [24] found that common risk factors mediate the consistency of cognitive function in couples. Risk factors for cognitive impairment, including history of exposure to smoking, Physical inactivity, a history of head injury, and major depressive disorder (MDD) were consistent among spouses. And physical inactivity, a history of head injury, and MDD have been found to mediate the association between spousal cognitive disorders and cognitive functions, including memory and executive function [24]. A recent study [25] suggests that differences in risk factors during midlife may explain cognitive impairment in spouses, but having a cognitively impaired spouse is not necessarily associated with an increased risk of incident dementia. Further research is recommended in three areas of relevance to neurology and psychiatry, as proposed by Peter et al.: assortative mating, dyadic lifestyles, and spouse caregiving [26]. The shared risk factors between spouses provide new ideas and methods for early prevention and intervention.

DISCUSSION

In a systematic review and meta-analysis investigating cognitive impairment in elderly couples, it was found that spouses of individuals with cognitive impairment experienced a more pronounced decline in cognitive function compared to those with normal cognitive abilities, as evidenced by an effect size (Cohen’s d) of –0.35 (–0.46, –0.23). Additionally, individuals whose spouses had cognitive impairment were at a higher risk of cognitive decline, with an effect size (OR) of 1.42 and a 95% confidence interval (CI) of 1.15 to 1.76. The absence of publication bias was confirmed by Egger’s test, which resulted in a p-value greater than 0.05. Notably, several diseases often exhibit comorbidity between spouses, and cognitive impairment demonstrates consistency among spouses as well [10 , 29]. To explain this spousal congruence in risk factors for cognitive impairment, three theories have emerged in the literature. Firstly, caregiver stress theory suggests that the demands of caregiving may contribute to cognitive decline in spouses [30]. Secondly, assortative mating theory posits that individuals may select partners with similar characteristics, including cognitive abilities, leading to shared vulnerabilities [31]. Lastly, the effects of long-term cohabitation and shared environments are proposed as factors influencing the convergence of lifestyle and environmental factors, resulting in spousal similarity in cognitive impairment risk [3].

The influence of age on cognitive impairment in the elderly is widely recognized, with advanced age being associated with an increased likelihood of experiencing cognitive decline [31]. Consistent with previous reviews [32], our analysis indicates that spouses of individuals with cognitive impairment exhibit more severe cognitive decline compared to age-matched individuals. This disparity suggests that the chronic stress associated with caregiving for individuals with cognitive impairment may contribute to one’s own cognitive decline. Stressors have the potential to induce cognitive and emotional changes. This is primarily attributed to the heightened inflammatory processes triggered by chronic stress, which diminishes the sensitivity of immune cells to the inhibitory effects of glucocorticoids, resulting in glucocorticoid resistance [33]. Systemic inflammation, characterized by persistently elevated levels of proinflammatory cytokines and chronic activation of the immune system, underlies various age-related diseases, including cardiovascular disease and dementia [34]. When one member of the couple suffers from cognitive impairment, the spouse needs to take on more responsibility and supervision, which will undoubtedly increase the burden on the spouse itself. Van et al. [35] noted in their systematic review that the level of burden among spouse caregivers of people with cognitive impairment remained moderate but increased dramatically over time. The magnitude of this increase was greatest, with specific factors such as being a spouse, increased behavioral disorders in the patient, and decreased ability to perform daily living increasing the risk of burden. This burden undoubtedly accelerated the decline of their own cognitive function. In the literature we included [17 –20] have also identified mediating factors between psychological complaints such as depression and anxiety, metabolic risk, caregiver stress, and cognitive impairment. Wu et al. [34] proposed a biopsychosocial model in their research to elucidate how stress-related pathways contribute to cognitive decline. This provides a basis for identifying stress risks in spouses of individuals with cognitive impairments and inhibiting abnormal cognitive aging.

Assortative mating and shared lifestyle and environmental factors provide additional explanations for the consistency of cognitive impairment among couples. Domingue et al. [36] explored the genetic similarity between couples across the genome and found evidence that individuals tend to select partners who are similar to themselves. However, further research is needed to investigate the relationship between genetic traits and the consistency of cognitive impairment among couples.

Several studies [37 –39] have demonstrated that couples share a common environment, including living arrangements, dietary habits, and lifestyle choices. These shared factors, such as alcohol consumption, smoking levels, physical activity, and daily routines, can influence each other’s health outcomes and may contribute to the congruence of diseases between couples. However, the two studies [24, 25] we included in our analysis reported spousal agreement on risk factors for cognitive impairment. Lee et al. [25] found that midlife risk factors, such as education, smoking, alcohol consumption, physical activity, BMI, and hypertension, explained the link between spousal cognitive impairment and mild, though statistically significant, deficits in baseline cognitive performance in late life. Yang et al. [24] examined common risk factors for cognitive impairment among couples, such as age, education level, smoking, history of head trauma, lack of physical activity, and depressive symptoms. After adjusting for age and education level, they identified history of brain trauma, physical inactivity, and major depression as independent risk factors for cognitive impairment, mediating the association between spouses with cognitive impairment and the risk of cognitive decline. By providing a comprehensive description of these three aspects, we aim to better understand the risk factors for cognitive decline in elderly couples. This knowledge can help identify relevant risk factors and develop appropriate intervention measures.

Limitations

This review acknowledges several limitations that should be considered when interpreting the findings. Firstly, the search strategy and inclusion criteria were limited to English-language papers, which may have resulted in the exclusion of relevant studies in other languages. Secondly, the included studies predominantly consisted of observational case-control and cross-sectional designs, with limited longitudinal studies. This makes it challenging to establish causal relationships and draw definitive conclusions about the causal effects of the identified risk factors. Furthermore, the heterogeneity in cognitive assessment tools and diagnostic criteria across different studies posed challenges in conducting a comprehensive analysis. Only total cognitive scores were included in the meta-analysis, while specific domains of cognitive impairment such as orientation, memory, and language function were not individually assessed. Additionally, this review qualitatively describes studies related to risk factors for cognitive decline in couples, but due to insufficient data availability, a meta-analysis could not be performed.

Conclusion

This systematic review and meta-analysis provide evidence on cognitive decline occurrence and risk factors in couples. Spousal cognitive impairment is identified as an independent risk factor, with lower cognitive function scores observed in spouses with cognitive impairment. The presence of cognitive impairment in one partner increases the risk of cognitive decline in the other partner. Mediating factors include the physical and mental stress of caregiving and shared risk factors between couples. However, further research is needed to understand the impact of caregiver stress and shared risk factors and to develop targeted interventions. Therefore, it is crucial to implement early screening and assessment of cognitive function in both spouses within a family unit, enabling the timely identification of these risk factors and the implementation of appropriate intervention measures. Additionally, further research efforts should be directed towards exploring additional factors that may contribute to cognitive decline in couples, ultimately leading to the development of targeted interventions aimed at improving cognitive health within this population.

AUTHOR CONTRIBUTIONS

Hongyan Meng (Conceptualization; Data curation; Formal analysis; Writing – original draft; Writing – review & editing); Xiangru Lv (Conceptualization; Writing – original draft; Writing – review & editing); Rong Zhang (Data curation; Validation); Yuping Feng (Conceptualization; Data curation); Jing Wang (Conceptualization; Data curation); Jia rui Liu (Data curation; Methodology); Juxia Zhang (Formal analysis; Funding acquisition; Writing – original draft; Writing – review & editing).

Footnotes

ACKNOWLEDGMENTS

The authors have no acknowledgments to report.

FUNDING

This work was supported by the National Natural Science Foundation of China (72264002), the China Medical Education Association Project (2022KTZ010), the Natural Science Foundation of Gansu Province (21JR7RA607 and 21JR7RA613), and the Scientific Research Foundation of Gansu Provincial Hospital (22GSSYD-69 and 22GSSYD-70).

CONFLICT OF INTEREST

The authors have no conflict of interest.

DATA AVAILABILITY

Data will be made available on request.

The supplementary material is available in the electronic version of this article: .

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