Increasing population ageing is undoubtedly a huge challenge for both developed and developing countries (1). In the upcoming 25 years, China will become a “super senior society,” with 24.71% of the geriatric population (aged 65 and over), and a significant increase in the proportion of older adults living alone (2). Influenced by traditional Chinese culture, co-residence between the older adults and their children is a core component of the Chinese family aging model. However, with the increasingly obvious trend of family nucleation, the weakening of traditional family values as well as the fading of filial piety culture, the residence pattern of the older adults has also changed significantly, and the number and proportion of older adults living alone is rapidly increasing. Additionally, the proportion of older adults persons (65 years of age or older) who live alone grew from 6.1% in 2010 to 7.5% in 2019 and is expected to continue rising (3).

Unfortunately, a number of medical, psychological, and social issues are linked to older persons who live alone (4), such as feeling isolated (5), experience loss of function (6), socioeconomic disadvantage (7), and even a higher risk of suicide. Barraclough discovered that the prevalence of suicide among older adults was more strongly associated with living alone than with any other social variable (8). Other study had concluded that from 19 to 60% of older suicides lived alone at the time of death (9). Hu et al. (10) found the prevalence of suicidal ideation among older adults living alone to be 23.6%, much higher than the results of a meta-analysis of suicidal ideation among Chinese older adults by Dong et al. (11) which was 14.7%. Additionally, there is evidence indicating that a greater proportion of suicide completers reside alone as opposed to with their families (12).

The novel coronavirus infection (COVID-19) (13) has resulted in a reduction in social interactions and isolation due to its high transmissibility (14). The pandemic and associated physical distance measures weaken or even limit the possibilities for intimacy and affection with loved ones or friends (15), and the resulting reduction in social contact outside the home may result in the marginalization of older adults who live alone. During the pandemic, it is postulated that older adults who live alone may be at an increased risk of adverse health outcomes in comparison to those who live with others. This is attributed to a lack of direct support and access to basic health care, in addition to the reduced availability of routine services (16). It is probable that these factors will contribute to an elevated risk of suicide among older adults who reside alone. Given that suicidal ideation is the most significant predictor of suicide attempts and mortality in older adults, it is particularly important to address suicidal ideation among older adults living alone in China, especially in the context of COVID-19 pandemic.

Living alone usually leads to a variety of adverse physical and psychological changes that ultimately affect healthy aging and quality of life in older adults, one of the major adverse features of which is frailty (17). The term “frailty” has been employed in clinical contexts to describe a condition that commonly affects older individuals and is associated with impaired strength, endurance, and balance, along with heightened vulnerability to trauma and other forms of stress. It is also associated with an elevated risk for morbidity, disability, and mortality. The prevalence of frailty among individuals aged 65 and older is estimated to range from 10 to 25%, with the proportion increasing significantly with increasing age (18). The condition of living alone is frequently included as one of the criteria in a number of tools designed to assess social frailty or social aspects of frailty (19), and a study demonstrated that older adults with social frailty exhibited a heightened risk of developing physical frailty (20). The findings of a systematic review and meta-analysis indicated that older adults residing in their own homes in the community are significantly more prone to frailty in comparison to those who reside in other living arrangements (21). It has been demonstrated that frailty represents a significant risk factor for suicidal ideation among older adults (22). And some evidence has suggested frailty characteristics in older adults may lead to hastening the spiral of suicidal ideation (23). However, the underlying mechanism of the relationship between frailty and suicidal ideation has not yet been exhibited. Nevertheless, the underlying mechanism by which frailty is associated with suicidal ideation in older adults living alone remains unclear.

According to the development model of suicide trajectories, frailty as a somatic stressor (distal factor), its association with suicide may be mediated by further psychological stressors (proximal risk factors) (24). Previous studies found that the frailty in older adults with chronic diseases can lead to perceived burdensomeness, then developed into depression, frustration, etc., and even suicidal behavior (25), suggesting the potential effect of perceived burdensomeness in mediating physical risk factors and suicidal ideation. Perceived burdensomeness (PB) have been proposed by the Interpersonal-Psychological Theory of Suicide (26) as a proximal adequacy contributor to suicide ideation, especially in older adults. PB is a distorted perceptions that one is so incapable that one is a burden or liability to other people, and it became stronger with aging (26). These misconceptions can lead to shame, low self-esteem, and self-hatred, which can cause individuals to believe that their death is more valuable to those around them than their own survival (27). A previous study found that impairment in self-care and social functioning may be more strongly associated with perceived burden (28). Since older adults who live alone face more social isolations and self-care challenges, and frailty may impair their self-care functions, which can bring a greater sense of perceived burden. Therefore, it is reasonable to hypothesize that the association of frailty and suicidal ideation may be mediated by perceived burdensome in older adults living alone. However, the existence of positive buffering factors that may play a role in preventing the development of negative outcomes is suggested by the fact that not all frail older adults perceive distress and exhibit suicidal ideation. To reduce the risk of suicidal ideation, it is important to elucidate the mechanisms by which protective factors operate.

Positive emotions may be one of such protective factors. Positive emotions represent a psychological strength that can confer psychological adjustment, physical health, Fredrickson et al. (29). Based on the broaden and build theory of positive emotions, positive emotions help build psychological resources, support coping and problem-solving processes (30), and promote individuals’ rapid recovery from stress and enhance their ability to bounce back from adversity. Numerous studies found that positive emotions can buffer the relationship between stress-related risk factors and negative outcomes in general population, such as depressive disorder symptoms (31), and non-suicidal self-injury (32). The theory of socio-emotional selectivity proposes that the ability to regulate emotions increases with age as older adults give priority to emotional and relational goals (32). Gross and colleagues also proved that older adults experience fewer negative emotions than younger adults, increasing focus on the experience of positive emotions (33). Thus we hypothesize that the protective effect of positive emotions may be more pronounced in older adults who live alone, and it could moderate the relationship between frailty (somatic stressor), perceived burdensomeness (psychological stressors) and suicidal ideation.

Taken together, frailty, perceived burdensome and positive emotions all play an important role in the endorsement of suicidal ideation, but the possible influence of these mechanisms on suicidal ideation among older adults living alone in the community is not clear. The present study aimed at a mediating role model with moderating effects (see Figure 1), which examines the direct relationship between frailty and suicidal ideation as well as the mediating and moderating role of perceived burdensomeness and positive emotions. The hypotheses are as follows: frailty may develop into suicidal ideation either directly (H3) or through the mediating role of perceived burdensomeness (H1, H2), and the hypothetical paths can be moderated by positive emotions (H4, H5, H6).

The negative impact of frailty on suicidal ideation is increasingly supported by empirical evidence. However, the mechanisms underlying this association remain largely unexplored, especially among community-dwelling older adults. The present study found that frailty was significantly and positively associated with suicidal ideation and perceived burdensomeness could mediate the relationship. Furthermore, positive emotions significantly moderated the mediating role of perceived burdensomeness. These results support our hypothesis.

There is a limited amount of knowledge about the prevalence of suicidal ideation among older adults who live alone. In the present study, the prevalence of suicidal ideation among the older adults living alone in the community was 15.57% (139/893), which was significantly higher than the prevalence of community-dwelling older adults in Beijing (2.3%) (51), and that reported in a recent meta-analysis for general Chinese older adults[11.5% (range 2.2 to 21.5%)] (11). The prevalence of suicidal ideation is also higher in this study than in the Korean National Health and Nutrition Examination Survey [10.0% (123/1234)] for people aged 65 years and older (52). Thus, more attention should be paid to the prevalence of suicidal ideation among Chinese older adults living alone, which may be higher.

The prevalence of frailty among the older adults living alone was 50.73% in the study, higher than that of a study on the frailty of older adults people living alone in the Japanese community (male: 38.1%; female: 16.8%) (53). Consistent with findings from previous studies in a population of U.S. veterans aged 65 years or older (54) and older adults living in the community with major depressive disorder (55), the present study also found that frailty is a risk factor for suicidal ideation among Chinese older adults who live alone. Frailty reduces the ability of self-care and participating in social activities, thus may exacerbates the social isolation and loneliness that result from living alone, placing individuals at high risk for suicide.

Previous studies have shown that perceived burdensomeness is a strong and solid predictor in the development of suicidal ideation (55), especially in older populations, over risk variables such as depression (56). The present study confirmed that, i.e., perceived burdensomeness partially mediates the association between frailty and suicidal ideation, suggesting the importance of perceived burdensomeness in predicting suicidal ideation in frail older adults living alone. Furthermore, the mediating effect of perceived burdensomeness was still significant when controlling for depressive symptoms, suggesting a strong effect of burdensomeness on suicidal ideation. The studies regarding perceived burdensomeness in older adults have primarily included older adults experiencing dysfunction or physical illness (26). Some studies have found that perceived burdensomeness is significantly associated with suicidal ideation among older adults with life-limiting illnesses (57). As the interpersonal theory of suicide suggests, many older adults are more likely to experience feelings of burden as they age (26), and perceived feelings of burden may be particularly relevant to older adults (56). Specifically, many older adults experience a sense of distress as they begin to need more care from family members or friends, and the increased need for assistance from others may derive from a medical problem or loss of a job, resulting in an individual’s need for (and not generating) financial support or physical care. Receiving help may make some older adults feel like a burden to others (58). In such cases, some older persons may perceive themselves as a burden and may consider this state to be steadfast and permanent, leading to the consideration of suicide and death as a solution to the problem of ongoing burden (26). And the relationship between perceived burdensomeness and suicidal ideation caused by social, interpersonal and physical constraints may be a mutually enhancing process of decline in old age, increasing the sense of perceived burdensomeness among the older adults, hastening the spiral of suicidal ideation (54).

Therefore, older persons living alone, especially those with physical limitations such as frailty, deserve more physical care and more comprehensive psychological support. When diagnosing frail older adults, perceived burdensomeness can be evaluated firstly to predict the possibility of suicide risk by clinicians, and may help older adults to avoid the potential stigma of discussing suicide and increase engagement with clinical services (59). In addition, frailty and other medical comorbidities can be a valuable tool for clinicians in the identification and intervention of potential suicidal ideation, which may not normally be a topic of discussion, helping frail older adults at this critical time of mental pain and stress (55).

Additionally, the study found that positive emotions mitigated the impact of frailty on suicidal ideation directly, or through the path of perceived burdensomeness to suicidal ideation. This result was found to agree with a previous research conducted in a rural sexual minority group, which found that high levels of positive emotions weakened the pathway between perceived burdensomeness and suicidal ideation (60). An experimental study conducted in a student population also concluded that frustrated interpersonal needs, especially perceived burdensomeness, deplete the individual’s desire to continue living before suicidal ideation ensues, whereas positive emotions enhance enthusiasm for life and therefore resist suicidal ideation in the face of interpersonal adversity (61). This result can be explained by the broaden-and-build theory of positive affect, which implied that positive emotions can help broaden cognitive attention to potential coping resources, and thus to foster positive psychological adjustment (62). Positive emotions are also a source of resilience, which in turn promotes further positive emotions (63). A number of lines of evidence are in favor of the view that positive emotions and resilience are mutually reinforcing (64). On this basis, resilience may be used as a moderating variable to reduce or eliminate the correlation between risk (such as frailty and perceived burdensomeness) and suicide (65). Therefore, it is necessary to strengthen policy interventions in the areas of positive emotions in older adults, and enhancing positive emotional experiences in older adults is important to promote a sense of meaning in their lives.

There are some limitations to this study. First, the generalizability should be treated cautiously because Sample size was constrained, with participants from only one city in mainland China. Future studies may include older adults living alone from different regions or cultural backgrounds for confirmation of the results of this study. Second, this study depended on self-reported questionnaire data, therefore, recall bias and report bias was possible. Third, the present study was a cross-sectional study and failed to identify a possible causal link between frailty and suicide. Future studies could use a longitudinal study design to explore the relationship between the pair.

In our findings, the multiple moderating effects of positive emotions provide the feasibility of implementing a positive emotion intervention among older adults living alone in the community. Considering that most Chinese community healthcare facilities lack professional psychological counselors, nurses are more accessible to the older adults living alone and can be trained through psychological intervention techniques for them as a complement to psychological care in the daily care of the older adults living alone in the future study. By improving the quality of nurses’ psychological care competencies, it is expected to reduce the influence of risk predictors on suicidal ideation in older individuals living alone in the community. It is also necessary to maintain a sense of normalcy and rejuvenation in order to encourage the positive emotions of older adults to function and to promote “active and productive aging.” In addition, because perceived burdensomeness mediates the relationship between frailty and suicidal ideation, perceived burdensomeness can be assessed for frail older adults to predict the likelihood of suicidal risk in future clinical practice.

To summarize, our data indicate that frailty was related to suicidal ideation, and perceived burdensomeness practically mediated this association. This result supports the interpersonal-psychological theory of suicide in older adults living alone. In addition, the finding of positive emotions moderated the relationship among frailty, burdensomeness, and suicidal ideation in this study, supports the broaden-and-build theory of positive affect, and contributes to developing tailored suicide prevention strategies by enhancing positive emotions for older adults living alone. In the future, more research in this field may wish to explore positive psychological interventions. (e.g., positive emotions as a target for intervention) to enhance the emotional threshold of older adults living alone in the community and reduce suicidal ideation.