Moderating effect of instrumental activities of daily living on the relationship between loneliness and depression in people with cognitive frailty

Abstract

Background

The identification of depression and loneliness among people with cognitive frailty (CF) could prevent negative psychological and physical health outcomes. Few studies have focused on physical and mental health together, and little is known about the role of daily activity in the association between depression and loneliness among elderly individuals with CF.

Objectives

To determine the positive effect of loneliness on depression among community-dwelling older adults with CF as well as the moderating effect of instrumental activities of daily living (IADL) on this association.

Design, setting, participants, and measurements

This cross-sectional study included 529 adults aged 65 years and older from a community-dwelling population who were screened for CF and was conducted from July 2023 to December 2023. The participants were assessed via validation instruments for the following main variables: Short-form Geriatric Depression Scale, Loneliness Questionnaire, Athens Insomnia Scale, Instrumental Activities of Daily Living (IADL), Social Support Scale, and sociodemographic characteristics. The participants were classified as having reversable CF (RCF) or potentially reversable CF (PRCF).

Results

The IADL, depression, insomnia, and loneliness scores were lower among individuals with RCF than among individuals PRCF. The moderating effect of IADL scores shows that the relationship between loneliness and depression has a steeper and positive slope when lower levels of IADL exist, compared with a straight line when there are higher levels of IADL, for this case, the line is less steep and showed negative association.

Conclusions

The integrity of physical and social connections has a protective effect on the mental health of elderly people with CF. It is necessary to pay attention to disability and loneliness among elderly individuals. Targeted interventions for improving physical activity and social participation seem to be practical and feasible solutions to alleviate depressive symptoms.

Introduction

Owing to the rapidly ageing population worldwide, an increasing proportion of older adults will exhibit a decrease in functional status and increased risks of frailty and cognitive impairment, among other age-related conditions. Cognitive frailty (CF) is defined as the conjunction of physical frailty with cognitive impairment but not the presence of a neurological condition. CF is a potentially reversible condition and is not necessarily an intermediate stage between normal ageing and dementia [1]. Although individuals with CF do not have a clear clinical diagnosis, they can still present with multidimensional deficits, including depression, decreased function, loneliness, and social and physical frailty. A few studies have reported that CF is more strongly associated with adverse health outcomes, such as disability in basic activities of daily living, Instrumental Activities of Daily Living Scale (IADL), low quality of life, and death, than is cognitive impairment or physical frailty alone [2, 3]. On the other hand, compared with people who have already developed cognitive impairment, older adults with CF are relatively young, their physical functions are still intact, and their perceptions are normal. Therefore, they have a high demand for social participation, interpersonal communication, and a high quality of life, which we hope to help patients achieve [4].

The loss of physical and cognitive function may be related to the environment and can reflect the limited opportunities for older adults to participate at the community level [5].

An increasing number of studies have shown that elderly people with cognitive decline are vulnerable to loneliness, even if the association is bidirectional. An English longitudinal study of ageing revealed that the risk of frailty increases with increasing severity of loneliness [6]. Among Chinese community-dwelling elderly individuals, loneliness is a risk factor for cognitive impairment and physical frailty [7]. The potential reason for this association may be lifestyle factors (e.g., living alone, deceased friends and partners, chronic illnesses) that increase the risk of negative health outcomes associated with loneliness (e.g., poor immune function, mental health risks, heart disease) [8, 9]. Elderly individuals with CF often experience declines in physical function, reduced mobility, and sensory and perceptual difficulties [10]; furthermore, dwelling and social institutions are incapable of providing adequate facilities or municipal services as the global population ages, which has an isolating effect on individuals, as their ability to go out and engage in social activities may be compromised [11].

In addition to loneliness, mental health problems are commonly reported among individuals with CF. Late-life depression increases the prevalence of physical illness, reduces quality of life, causes many medical conditions, and exacerbates disability. From a clinical and public health perspective, the factors influencing depressive symptoms among older adults should be explored to facilitate the early detection of depression and improve quality of life [12]. Recent studies have suggested that 16%~35% of individuals with frailty also experience coexisting depression and that the prevalence of depression in older adults with frailty is as high as 46.5% [13]. Furthermore, depression could contribute to the development of persistent or progressive cognitive decline [14]. The incidence of cognitive decline comorbid with depression among elderly individuals is high, and both factors influence each other. It has been reported that cognitive impairment occurs in 85%~94% of patients with acute depressive episodes and in 39%~44% of patients after a depressive episode has subsided. Depression among China’s elderly population is associated with the trajectory of changes in cognitive function [15]. Cognitive decline can decrease a person’s ability to engage in activities, perception of social isolation, stress management, and negative emotions, all of which can contribute to aggravated depression.

As CF represents a decline in physical function, IADL, which includes cooking, laundry, transport, and finance management, are likely affected among individuals with CF. Deficits in performing these self-care-related IADL are more pronounced among elderly individuals, and this disability is independently associated with depression [16]. A cross-sectional study of 207 Japanese Americans (aged ≥ 68 years) revealed that older adults with high levels of functional status in IADL have lower odds of depressive symptoms (OR: 0.2, 95% CI: 0.09–0.50) [12]. People with disabilities in complex activities and with reduced efficiency of cognitive functions, who are more dependent on others, and who have greater deficits in self-care are more likely to be depressed. Research has confirmed that older people with more severe functional impairment are more likely to experience depressive symptoms [3, 17]. A longitudinal study from Western countries revealed that loneliness was associated with an increase in daily disability difficulties. It seems that loneliness and decreased daily living ability are common risk factors for depression. However, little is known about the associations among depressive symptoms, loneliness, and IADL disabilities among community-dwelling older people with CF.

Loneliness and depression are more common in elderly people with CF than in robust elderly people. Moreover, the ability to use tools among elderly people seems to be related to depression, but this relationship has not been examined in detail among individuals with both cognitive decline and physical frailty. The relationships among the deterioration of cognitive functions, physical functions, mental status, and independence in everyday life should be explored. Therefore, this study aimed to analyse the moderation effect of IADL on the direction from loneliness to depression among older adults with CF.

Methods

Study design

The study is a cross-sectional survey among community-dwelling elderly people with CF that was conducted in 2 communities in China, Beijing, from June 2023 to December 2023.

Study population

The participants were recruited as convenience sample.

Inclusion criteria

(a) were aged 65 years or above, (b) were able to complete the survey with aid from research assistants, and (c) provided informed consent and volunteered to participate. (d) identified as cognitive frailty, For the assessment of CF, the participants needed to meet the following requirements: (1) for cognitive decline, the MoCA score was < 26; for those with less than 12 years of education, 1 additional point was added to the original score, and the Clinical Dementia Rating Scale (CDR) score was 0.5; and (2) the Fried frailty phenotype score was ≥ 3 (this test assesses for physical frailty).

Exclusion criteria

(a) patients who were clinically diagnosed with dementia or mental health illness or (b) patients who were in the final stage of severe organ dysfunction and were therefore unable to complete the investigation.

Sample size

Given that the previous prevalence of CF was 10%, and the formula$\text{n}=(\text{Z}^{2}\times \text{P} \times (1-\text{P}))/\text{d}^{2}$, the minimum sample size for the cross-sectional survey would be 865 to screen elderly people for CF. Finally, we screened over 1000 community-dwelling individuals and 529 elderly individuals who were considered to have CF and were enrolled in the study.

Study hypotheses

We proposed the hypothesis (Fig. 1) that depression among people with CF has a direct effect on participants’ loneliness level, where the association was moderated by the Instrumental Activity of Daily Living (IADL) score.

Fig. 1

Study hypothesis, a direct acyclic graph

Measures

Demographic characteristics

The general sociodemographic information, including gender, age, education level, job status before retirement, living status, activity status, body mass index, chronic disease history, smoking and alcohol history, and medication usage, was recorded.

Cognitive function measures

Clinical dementia rating scale (CDR)

The Clinical Dementia Rating (CDR) was used to exclude participants who were identified as having mild to severe dementia. In the CDR, a 5-point scale is used to categorize six domains, including memory, orientation, problem-solving, community affairs, home activities, and personal care, from which a classification of global dementia staging is obtained. The five CDR classification groups included normal, mild, moderate, and severe dementia and early memory deterioration. A score of 0.5 on the CDR is defined as mild cognitive impairment [18]. Participants who scored 0 points were considered robust. Those who scored 1 to 3 (mild to severe dementia) were excluded.

The Chinese version of the montreal cognitive assessment (MoCA-Chinese Beijing version)

The MoCA was utilized to identify cognitive decline among participants. Patients with a MoCA score of ≥ 26 were classified as cognitively normal, whereas those with a score of < 26 were classified as having cognitive decline. To counterbalance the effect of lower education, 1 point was added to the final score of individuals with less than 12 years of education. Patients with MoCA scores ranging from 22 to 25 were classified as having mild cognitive impairment (MCI). The researchers conducting the MoCA assessment obtained certification through the official website. Data collection was performed by the same researcher to minimize measurement bias.

Subjective cognitive decline questionnaire (SCD-Q)

To assess subjective decline in memory, language, and executive functioning in the last year, we used the subjective cognitive decline questionnaire (SCD-Q). The SCDQ consists of 24 yes-or-no questions assessing the difficulty of performing activities requiring cognitive function in the past 2 years. The total SCDQ score ranges from 0 to 24, with a higher score indicating greater self-perceived cognitive decline. The SCD was assessed with the simplified SCD questionnaire [19, 20], and 2 questions involved memory and other domains. The pre-MCI indicator (SCD) was used if a positive response was given to 1 of 2 questions: “In the last 2 years, has your memory declined?” or “Has your other cognition declined? For example, have you had difficulty remembering family members’ or close friends’ names, finding your way around your neighbourhood, or handling money?”. In this study, we defined pre-MCI if the participants had a normal cognitive function test by the MoCA but self-reported cognitive decline.

Physical performance measure

Frailty phenotype

Physical performance was assessed and defined via a modified Fried frailty phenotype comprising five criteria: slowness, weakness, exhaustion, weight loss, and low activity [21]. On the basis of these criteria, the participants received a sum score ranging from zero to five. For each of the characteristics, one point is given if the measure is positive for frailty; in the absence of any characteristic suggestive of physical frailty, persons are robust, whereas persons with 3–5 characteristics are considered frail. The presence of 1 or 2 characteristics indicates a prefrail condition. In current study we only involved participants whose Fried frailty phenotype score was ≥ 3 (considered as physical frailty).

Determination of CF

The current study divided CF into two subgroups according to a new definition that broadened the CF spectrum [22]. Reversible CF (RCF) refers to the combination of physical frailty and pre-MCI (subjective cognitive decline), whereas the other subgroup is identified as potentially RCF (PRCF), which is the combination of physical frailty and MCI [8]. Otherwise, individuals who sustained normal cognition with nonfrailty, prefrailty or frailty only, subjective cognitive decline only, or MCI only were considered not to have CF (no-CF).

Short-form geriatric depression scale (GDS-15)

The short-form geriatric depression scale involves 15 items (GDS-15), which were extracted from the 30-item version, and a high correlation index was found between the GDS full and short forms (r = 0.91, P < 0.01). The Cronbach’s alpha was 0.7 [23], and it has been widely used to screen for depression among elderly individuals in nursing homes and medical institutions. The GDS-15 score ranges from 0 to 15, and higher scores indicate severe depression.

Loneliness assessment

Loneliness was evaluated by the question “How often do you feel alone?” The response was a 5-point Likert scale, where 0 means “not at all” and where 4 refers to “always”. Higher scores indicate a higher level of loneliness.

Instrumental activity of daily living (IADL)

The IADL scale, which consists of 8 questions, was used to evaluate instrumental living activities. The response spectrum is based on a 5-point Likert scale in the areas of telephone use (3 items), shopping (3 items), food preparation (3 items), home activities (4 items), washing clothes (2 items), transportation (4 items), drug administration (2 items), and financial management (2 items). The total score ranges between 0 and 23, and a higher score indicates greater abilities. The Cronbach’s alpha was 0.75 [19].

Athens insomnia scale (AIS-8)

The Athens Insomnia Scale contains 8 items, and the first five address the participant’s nighttime symptoms (difficulty in sleep initiation, difficulty in maintaining sleep and early morning awakening), whereas the last three items address the daytime impact due to any reported sleep disturbances. The respondents were required to provide a positive rating if they had experienced the sleep difficulty described in each item at least three times a week during the previous month. A maximum total score of 24, indicating the most severe symptoms of insomnia, was possible, whereas a cut-off point of ≥ 6 represented a minimum criterion for the confirmation of insomnia symptoms [24].

Social support scale (SSRS)

The scale was developed to assess how much support respondents received from their family, friends, and social contexts, and the SSRS consists of 10 items with a total score of 60. The level of social support that individuals expect and receive can be understood through this scale. A higher score on the SSRS indicates a better level of social support. The Cronbach’s alpha for the present study was 0.788 [25].

Lubben social network scale

We used the Lubben social network scale to measure individuals’ perceptions of social engagement, including family and friends, via self-reports. The scale consists of 12 items, with responses to each item ranging from 0 (less social engagement) to 5 (more social engagement). A higher total score indicates more social engagement. The Cronbach’s alpha for the LSNS is 0.7 [26].

Statistical analysis

First, the demographic characteristics were analysed by number and percentage, and the other data collected were analysed via descriptive analysis of means and standard deviations for each variable to be analysed. We divided participants into 2 subgroups on the basis of CF type (RCF vs. PRCF), and the R×C χ² test was used to compare the differences between the two subgroups. Second, Spearman correlation analysis was conducted among the variables, which were sleep, loneliness, IADL, social net, social support, age, and depression. The linear regression models reported in the study considered depression as the dependent variable, and three models were calculated. In the first model, sleep, loneliness and social networks were selected for the model. The second model included the moderation variable of IADL, and the third model included the moderation effect of IADL and loneliness.

The statistical method of the third model included moderation analysis via the PROC REG step in SAS 9.4. For the moderation effect, variables were centred on the mean, and interactions were created by calculating the product of loneliness and IADL. The linear regression analysis incorporated two variables and a moderation variable. To determine significant interactions, a simple slope analysis was performed at low (− 1 SD) and high (+ 1 SD) levels of the moderator. Hypotheses were tested on the basis of confidence intervals, effect sizes and significant interactions (P < 0.05).

Ethical consideration

The assistant-aided questionnaires were collected anonymously without identifying information from the participating elderly individuals. The researchers explained the purpose and significance of the study, inclusion criteria, and right of elderly individuals to refuse to participate. The participants will be informed of the study objectives, and they signed a written informed consent form. The protocol will comply with the ethical principles of the 1964 Declaration of Helsinki, as revised in 2013 at the 64th WMA General Assembly in Fortaleza, Brazil [20], and standards of good clinical practice, and the study will comply with current legislation.

This research was reviewed and approved by the ethics committee of the Peking Union Medical College Hospital on 8 October 2022 (project: National High Level Hospital Clinical Research Funding, approval number: 2022-PUMCH-B-130). After ethical approval was granted to conduct the study, data were collected from July 2023 to December 2023. The elderly participants spent approximately 15 to 20 min completing the questionnaire with the help of research assistants, and the principal investigator was available to answer the questions during the data collection process.

Results

Participant characteristics

A total of 529 elderly individuals considered to have CF were included in the final statistical analysis. As mentioned before, participants were divided into two subgroups, there were 146 people recognized as potential reversible CF and 383 in the group of reversible CF. the average age in each group was 84.18 ± 5.32 and 80.27 ± 6.24, elderly who living with family in potential RCF reached at 112 (76.03%) and 303 (79.11%) in reversable CF group. The mean scores of depression were 3.00 ± 1.89 and 2.67 ± 1.30 respectively. The level of IADL in each group was averaged at 11.71 ± 4.19 and14.01 ± 3.67. The average score of Athens Insomnia Scale was 4.00 ± 1.94 for all participants, and the Social Support scale was scored at 29.58 ± 4.37 and 31.56 ± 2.76 for each group. Descriptive statistics of demographics, sleep, depression level, IADL, and loneliness are presented in Table 1, and comparisons of those variables based on the type of CF were also conducted.

Table 1 Demographic characteristics of cognitive frailty elderly (N = 529)

Age, IADL score, job type, and education level were significantly different between the subtypes of CF. A comparison of the characteristics of PRCF individuals (N = 146) and RCF individuals shows that the PRCF individuals were older (84.18 vs. 80.27, P < 0.001), the level of dependability indicated by IADL scores was worse for PRCF individuals than for RCF individuals (11.71 vs. 14.01, P < 0.001), and percentages of individuals with bachelor’s degrees were more in group of RCF individuals (39.17% vs. 22.60%, P < 0.001). The levels of depression and insomnia were higher among PRCF individuals, and most RCF individuals experienced a lower degree of loneliness and a stronger social net.

Preliminary analyses

Table 2 shows the results of the Spearman correlation analysis. All the key variables were significantly correlated with one another, and moderate-strength associations were observed between IADL, age, and depression. The correlations between sleep, depression, loneliness, and age were weak.

Table 2 The correlation analysis of variables (N = 529)

Moderation analyses

The level of IADL was found to moderate the relationship between loneliness and depression (Table 3). The three models presented in Table 3 indicate the regression coefficients of the variables that were considered in the hypotheses of this study. In Model 1, only the control and independent variables were considered, and both variables were significant. In the case of sleep, the regression coefficient was β = 0.04, P < 001; for social networks, the regression coefficient was β=-0.02, P = 0.03; and for loneliness, the regression coefficient was β=-0.02, P = 0.03. In Model 2, we added the moderation variable IADL to the regression analysis. The regression coefficient for sleep was β = 0.036, P = 0.02; for social networks, the regression coefficient was β=-0.013, P < 0.01; for loneliness, the regression coefficient was β = 0.145, P = 0.02; and for the moderator IADL, the regression coefficient was β=-0.191, P < 0.01. In Model 3, which was based on Hayes’ linear regression analysis, we added the interaction variable of IADL * loneliness, which yielded a significant coefficient of β=-0.116, P < 0.01. Most of the variables included in the model were significant, except for social network (β=-0.024, P = 0.19). The regression coefficient for the interaction of IADL* loneliness was β=-0.116, P < 0.01, which indicated that the effect of the moderator IADL on the relationship between loneliness and depression significantly differed on the basis of the IADL.

Table 3 Moderation graph of the moderation for the effect of IADL in the relationship between loneliness and depress (N = 529)

Finally, Fig. 2 shows the moderation effect of IADL. The relationship between loneliness and depression has a steeper and positive slope when lower levels of IADL exist, compared with a straight line when there are higher levels of IADL, for this case, the line is less steep and showed negative association.

Fig. 2

Moderation effect of IADL in the relationship between loneliness and depression

Discussion

This study aimed to examine the moderating effect of IADL on the relationship between loneliness and depression. On the basis of previous reports on the psychological, physiological, and social factors of elderly populations, further exploration of regulatory factors has provided insights beyond the flat description results, and studies have examined factors associated with the characteristics of people with CF. This study further highlights the integration and mutual influence of the weakened population from multiple perspectives, including social, physiological, and psychological perspectives, thus suggesting that there is a synergistic effect of physical health and social participation on the mental health of elderly individuals. The results reported in the current study contribute to the literature by examining the characteristics and heterogeneity between different stages of CF in people. Furthermore, we found that the association between loneliness and depression is mediated by IADL.

The present study suggests that several sociodemographic factors could significantly influence CF from potentially reversible to reversible. We found that the population with higher IADL scores is relatively young and has higher levels of education, although the correlation between the latter two factors was not statistically significant in this study. The average age of our participants was over 80 years, and older age was severe risk of CF, which inevitably led to a high incidence of geriatric syndrome, as most of the elderly reported insomnia, depressive symptoms, and worse physical ability than did those reported in previous studies [27, 28]. As the ageing population continues to accelerate, the number of older adults with CF will increase substantially due to age-related biological changes. CI and PF are representative common geriatric syndromes, and these two syndromes have a vicious cycle relationship [29]. Consistent with the above viewpoints, our results also indicated that age is a greater risk factor for CF than MCI and physical frailty are [30]. Our study is consistent with a systematic review and meta-analysis that found a positive correlation between the number of years of education and cognitive function later in life [31]. People with higher education levels may not expect to experience multimorbidity, as their peers are relatively healthier than people with lower education levels are and thus experience a greater impact on lifestyle and health value when they participate in nonhome-based activities as much as possible [32].

The continued progression of CF can lead to a decline in an older person’s ability to perform daily living activities, increasing the risk of adverse health outcomes such as social isolation, depression, incapacity, dementia and even death [33]. This led to the suggestion for the inclusion of cognitive function in frailty assessments to improve the identification of adverse outcomes among frail older adults [34]. Furthermore, understanding which interventions can help delay or RCF in older people may be important for reducing adverse outcomes [35]. Elderly people with cognitive decline prefer not to attend social events, severe physical ability and movement barriers somewhat hinder elderly people from participating in social interactions, and living separate from family members leads to loneliness and depression [36]. These findings are consistent with our results [37], and further exploration of potential reasons may be due to social isolation.

A person’s health status and loneliness are interrelated, as loneliness can lead to pain, depression, and mental health problems [38]. Older people who reported greater feelings of loneliness were eight times more likely to experience worse mental health than those who experienced less loneliness. The older adults in our study may have experienced a loss of relationship or interest. Moreover, evidence has shown that the absence of an intimate relationship results in a greater level of loneliness [39]. Some informal social support, such as group integrated intervention programs, could not only improve their social interactions but also strengthen their cognitive and physical capabilities [40]. Active engagement in social and cognitive activities was found to be negatively related to both loneliness and hopelessness in older Chinese people [41].

The novelty of this study lies in the finding that IADL is associated not only with depression and loneliness but also with the balance between the two mental health conditions. When IADL is involved in the path to depression, better performance in managing daily life, transportation, finances, outdoor activity, and medication adherence could mitigate the impact of loneliness on depression to some extent. The negative moderation effects may be associated with multiple factors.

On the one hand, some domains of IADL, such as managing finances and outdoor activities, are closely correlated with executive functions, such as sequencing and inhibition, and these domains show the largest discrepancy between those living with cognitive impairment and those living without impairment [12]. The functional capacity of older adults has been defined as their main health indicator by the World Health Organization. Higher-level competence may be more complex and difficult to achieve than IADL; therefore, older adults should maintain higher-level competence to be independent in their daily lives for as long as possible. Previous studies have reported that both physical frailty and MCI are associated with IADL impairment and that CF increases the risk of IADL impairment [31]. In addition, evidence has shown that greater cognitive performance is linked with better mental health. These results are consistent with those of previous studies showing that loneliness is associated with functional limitations and disabilities and suggest that the transition to a disabled state may trigger an increase in depressive symptoms [42]. Our study emphasizes the need to carefully examine individual domains of IADL disability and advanced interventions related to physical ability and physical exercise. Tailored services should be provided to older people with frailty in more complex tasks (e.g., financial and medication management and transportation) that require executive functioning [43].

On the other hand, elderly people with a low IADL score may be unable to experience many social activities as their heathy peers [44], which negatively affects their mental health. Physical disability may reduce their opportunities to participate in or complete daily life tasks alone, which may also be one of the factors that reduce IADL. At older ages, loneliness might not have the same impact on depression, as people tend to feel that their social circumstances compare favourably in terms of earlier expectations or relative to peers [41]. Maintaining moderate social activity and regular physical exercise is effective in postponing IADL disability [45]. According to activity theory, human beings need a sense of achievement and belonging within the social network, and elderly people are inclined to participate in activities that strengthen their social integration and adaptation. A Japanese cohort study indicated that elderly individuals with functional disabilities were less engaged in community management and activities, which implied that solitary status may lead to a decline in IADL function [46].

Nevertheless, the effect of social participation on physical and psychological well-being suggests the need to provide increased social support through community-based programs, especially for those who are at risk of social isolation and loneliness due to a lack of resources (e.g., volunteer activities, home visitation and transportation services). Additionally, increased social activities contribute to preserving cognitive function by providing various neurobiological stimuli caused by environmental complexity. Finally, an extensive social network could decrease the risk of depression, which has been shown to be a risk factor for frailty [47]. Additionally, earlier screening is recommended for depression, which prevents older adults from engaging in social activities.

An important contribution of this study is that living arrangements modify the associations of loneliness with depression among people with CF, which has not been reported before [48]. In future research, scales with good reliability and validity should be adopted to evaluate more dimensions of loneliness, and factors associated with dynamic changes in loneliness should be further investigated. Loneliness has different impacts on older adults’ health according to different living arrangements, ages, and sexes. One explanation for the moderating role of IADL may be that individuals at higher independent levels could act as a mechanism for reducing depression in other ways, such as social participation or physical activity. Loneliness has been related to psychological functional effects and mainly to the possibility of developing depression. Another perspective is that loneliness among elderly people cared for by domestic helpers may be related to family separation; therefore, developing corresponding interventions to improve physical and social support would be important for elderly people in the community. Therefore, these factors need to be considered when related policies are formulated at the familial and societal levels. Although the evidence provided important insights into social risk factors for CF among older adults, the findings were mostly from cross-sectional studies, and longitudinal studies are needed to examine causal relationships between social participation and CF incidence.

Limitations

Although the sample size in this study is considered adequate, the results may not be generalizable since a nonprobability sample was used after the districts were selected. In addition, the small sample size could have affected the study results. The questionnaire provides a general picture of how older people perceived their SRH, their sense of loneliness, and their level of IADL. Second, loneliness was assessed via one single question but not a scale, which made it difficult for us to evaluate other dimensions (e.g., the varying degrees) of loneliness and may have caused some bias.

Finally, the current cross-sectional design study could not provide a reasonable explanation for whether loneliness among people with CF is caused by depression and how IADL moderates this relationship; further longitudinal studies are needed to explore the causal relationship. Patients should be followed over time to assess whether they are losing skills and whether ceasing IADL or reducing cognitive fragility and reduces loneliness and/or depression.

Conclusion

In summary, older individuals with CF experience poor mental health and loneliness when living separately from their family. The extent to which loneliness negatively influences depression depends crucially on individuals’ functional limitations (IADL), with the IADL being more changeable by intervention than by psychological factors. This highlights the differences in social support and loneliness between elderly people living alone and those living with family. We should pay attention not only to the population with low IADL abilities but also to the importance of early cognitive and physical exercise interventions and to try to delay the time when elderly people lose their daily social and life abilities through exercise and social participation.

By targeting older people with CF who show signs of depression or loneliness, interventions could be promptly implemented to prevent worsening or even reversing the condition. These findings may increase awareness of the functional and mental health implications of community-dwelling older adults with CF and highlight the need to design multidisciplinary care interventions that consider differences in age, education, and cognitive function. Translating the study findings into concrete actions, such as redirecting care efforts related to physical function and social connection, will lead to a further positive impact on the life of individuals, offering them a successful ageing perspective despite health limitations. Furthermore, longitudinal research is needed to continue investigating this topic, and investigating this topic contributes to investigating the causal association between depression and loneliness among older adults.