Social support and subsequent cognitive frailty during a 1-year follow-up of older people: the mediating role of psychological distress

Frailty and cognitive impairment are two common geriatric symptoms linking adverse health-related outcomes [1]. However, cognitive frailty, a new definition proposed by the International Academy on Nutrition and Aging (I.A.N.A) and the International Association of Gerontology and Geriatrics (I.A.G.G) in 2013, was defined as “a heterogeneous clinical condition characterized by the simultaneous presence of both physical frailty and cognitive impairment and the exclusion of concurrent Alzheimer disease or other dementias” [2]. Increasing studies have shown that cognitive frailty plays a better role in predicting the short-term and the long-term all-cause mortality, disability, dementia, and other adverse health outcomes among older people than just frailty or cognitive impairment [3‐6]. Importantly, the condition of cognitive frailty could recovery physically robust and/or cognitively normal due to its reversible process if effective interventions were employed [7]. Therefore, it is imperative to identify predictive and modifiable risk factors and underlying mechanisms concerning cognitive frailty in order to inform intervention strategies among older people. However, to date, the possible determinants as well as the underlying mechanisms of cognitive frailty among older people are still poorly understood.

One potential modifiable protective factor for cognitive frailty among older people is social support [8], which is defined as “the perceived and actual assistance that individuals can receive from family, friends, and other connections in the social environment” [9]. Many studies have shown that social support is associated with increased risk of both physical frailty and cognitive impairment among older people [10, 11]. However, previous studies on the association between social support and cognitive frailty are predominantly cross-sectional [12, 13], we found no prospective study specifically examined the longitudinal association between social support and subsequent cognitive frailty among older people in rural China. Identifying mediating factors could be important to further understand the relationship between social support and cognitive frailty. The psychological process driving the link between social support and cognitive frailty is not clear. Previous studies in other countries have shown that psychological health is associated with both of cognitive frailty [6] and social support [14], suggesting that the association between social support and cognitive frailty might be through psychological mechanism. While prior studies have investigated the direct effects of both social support and psychological health on cognitive frailty separately, no study has investigated potential mediating effects of psychological health on the link between social support and cognitive frailty among older people. In addition, previous studies have shown that psychological health plays an important mediating role in relationships between some factors and health [15, 16]. A recent study has shown that the relationship between cognitive function and physical frailty is partially mediated by psychological distress [17]. Consequently, one of the underlying mechanisms between social support and cognitive function might be through psychological distress.

Using the longitudinal data from the Shandong Rural Elderly Health Cohort (SREHC), the current analysis was conducted to understand the link between social support and subsequent cognitive frailty over 1-year follow-up. Specifically, our first aim, as part of the search to prove the main hypothesis (the second aim), was to examine whether lower levels of social support increased the risk of cognitive frailty among older people during the subsequent year. As our main objective, the second aim was to examine the main hypothesis that psychological distress meditated associations of social support with cognitive frailty.

Table 1 presents the characteristics of the respondents according to cognitive frailty at baseline. Of the 2785 respondents, the average age was 69 years and most of the older adults were female (63.55%), illiterate (41.80%), and married (75.04%). At baseline, 6.71% of participants had cognitive frailty. At 1-year follow-up, the rates of cognitive frailty were 7.47%. Participants with cognitive frailty scored significantly higher on K10 (22.41 ± 9.19 vs. 16.22 ± 7.12, t = − 11.23, P < 0.001) and lower on social support (39.07 ± 7.07 vs. 43.39 ± 6.11, t = 9.23, P < 0.001) than those participants without cognitive frailty at baseline, respectively.

Table 2 presents the unstandardized path coefficients (a, b, c’, and c) of subsequent cognitive frailty in relation to social support mediated by psychological distress. The path coefficients related to binary outcomes were presented in log-odds unit. In the unadjusted models, social support was negatively associated with psychological distress (a path in the unadjusted model: β = − 0.176, 95% CI = − 0.225 to − 0.136, P < 0.001) and was negatively associated with cognitive frailty (c path in the unadjusted model: β = − 0.080, 95% CI = − 0.100 to − 0.061, P < 0.001). The effect of social support on cognitive frailty was attenuated after adjusting for psychological distress (c’ path in the unadjusted model: β = − 0.067, 95% CI = − 0.088 to − 0.047, P < 0.001). Univariate analyses showed that the log-odd of cognitive frailty was significantly higher in older people who were having lower social support score. Both a*b and c’ were negative and significant when predicting from social support. A partial mediation relationship was supported for cognitive frailty, with a ratio of a*b/(a*b + c’) was 18.29%.

After controlling for sex, age, education, marital status, economic status, smoking status, alcohol drinking status, chronic conditions, ADL, and cognitive frailty at baseline, we found that social support was negatively associated with cognitive frailty (path c in the adjusted model: β = − 0.040, 95% CI = − 0.064 to − 0.016, P < 0.001). When further adjusting for baseline psychological distress, social support was also negatively associated with psychological distress (path a in the adjusted model: β = − 0.098, 95% CI = − 0.137 to − 0.066, P < 0.001), and the direct effect of social support on cognitive frailty (coefficient c’) was reduced (c’ path in the adjusted model: β = − 0.028, 95% CI = − 0.053 to − 0.007, P < 0.001), which suggested social support played protective roles in psychological health and cognitive frailty. All path coefficients including a, b, c’ and c were statistically significant when predicting subsequent cognitive frailty from social support (the adjusted models in Table 2), suggesting that the protective effect of social support on cognitive decline may be mediated by psychological pathway. Specifically, the magnitude of direct effects of low social support on cognitive frailty changed from c’ = − 0.067 to − 0.028. The magnitude of mediation effects from social support to cognitive frailty via psychological distress changed from a*b = − 0.015 to − 0.009, and the ratio of a*b/(a*b + c’) was 24.32%. These results suggested that psychological distress partially mediated the relationship between social support and subsequent cognitive frailty, which was further confirmed by Bootstrapping tests. The results from Bootstrapping test showed that the 95% confidence interval of the indirect effect and direct effect did not span zero, indicating both the indirect effect and direct effect were statistically significant.

To our knowledge, this is the first study to prospectively examine the association of social support with subsequent cognitive frailty in a sample of rural Chinese older adults, as well as the mediating role of psychological distress in this process. There are two key findings. First, social support at baseline was significantly associated with decreased risk of subsequent psychological distress and cognitive frailty over 1-year follow-up. Second, the association of social support with cognitive frailty was partially mediated by psychological distress.

In this study, we also provided evidence about the prevalence of the cognitive frailty in rural China. We found the prevalence of cognitive frailty among rural Chinese older adults was approximately 7%, which was in accordance with previous studies using a similar definition in measurements (i.e. physical frailty was defined by phenotype criteria and cognitive impairment was defined by the MMSE) [30, 34]. However, one study using the data from the China Comprehensive Geriatric Assessment Study reported 2.3% of the prevalence of cognitive frailty, which is lower than our current study [35]. A possible explanation is weakness, as one of the important items in the measurement of frailty criteria, is not included in that study, which may underestimate the prevalence. Liu et al. [36] found that the prevalence of cognitive frailty is 13.3%, which is higher than the current study. One possible explanation is that Liu et al. included an older age group (≥ 65; mean age: 73) than our study. Previous studies and our research all suggest that cognitive frailty in Chinese older adults is not uncommon.

Social support is believed to be an important determinant of healthy ageing. A considerable body of epidemiological research has documented the health benefits from social support, such as lower mortality risks, better psychological and physical health outcomes [37‐39]. The association between social support and cognitive frailty has been shown by a handful of cross-sectional studies [12, 13]. For example, in a study of 815 older adults aged 60 years and above in Malaysia, Malek et al. found that social support is significantly associated with decreased risk for cognitive frailty (β = − 0.021, P < 0.001) [12]. To our knowledge, there are no prospective studies that have specifically examined the association between social support and subsequent cognitive frailty among older people. In the current study, we found the rates of subsequent cognitive frailty over 1-year follow-up increased with lower social support (path c and c’). Social support has been considered as a trait factor that has positive consequences for health and well-being by providing people with access to various tangible, health-enhancing resources, including, but not limited to, esteem, control, and connection [40]. These psychological resources have been found to be particularly beneficial in helping people to cope with a range of challenges, such as depression and anxiety, which in turn can affect cognitive frailty. Our finding highlights again the importance of assessing and intervening in social support for older people because it is a modifiable predictor for cognitive frailty.

Our mediation analysis showed that the association between social support and cognitive frailty was mediated by psychological distress, which could explain the longitudinal association between social support and cognitive frailty in part. Specifically, older people with higher levels of social support were associated with less psychological distress (path a), which, in turn, lead to attenuated odds of cognitive frailty (path b). This suggests that people with lower social support have more likelihoods of cognitive frailty in part because they have worse psychological health. There is substantial evidence that those with higher social support have better psychological health than those with less social support [14, 41‐44]. For example, Bai et al. reported social support does not promote the physical health of the Chinese elderly in rural areas, but it has a significant positive impact on their mental health [41]. Higher levels of social support mean meaningful interpersonal relations, Yang et al. found meaningful interpersonal relations may directly reduce psychological stress levels and in turn provide positive psychological implications such as enhancement of endocrine and immune functioning [45]. However, few studies have focused on the relationships between psychological factors and cognitive frailty. Only in a recent cross-sectional survey, the authors found mood disorder symptoms are strongly associated with cognitive frailty among community-dwelling people aged 60 years and over [6]. This is the first study to report psychological distress as a mediator in relationship between social support and subsequent cognitive frailty among Chinese older people. Our findings underpin the conceptual model of social relationships proposed by Berkman [46]. The model hypothesizes that health is impacted by social relationships through a series of causal processes that begin at the macro-social level (upstream factors) to micro-psychobiological processes (downstream factors). In the social network framework, psychological factors such as self-efficacy, self-esteem, depression, psychological distress, and sense of well-being represent some of the “downstream” pathways linking social relationships to health. Our study provides the evidence that social support as one of the “downstream factors” of social relationship can affect older adults’ cognitive frailty by psychological pathway (i.e., psychological distress). Psychological distress may serve as a negative form of the robust positive effects of social support on cognitive frailty in this population. Also, this finding suggests the importance of screening for psychological distress and providing strategies to mitigate the effects of poor mental health in later life. Further neurobiological and behavioral research is needed to better understand the underlying mechanisms between social support, psychological distress, and cognitive frailty among older people.

The current study has several strengths. The first strength is the longitudinal design that allows us to look at the association between social support and cognitive frailty over time. The second strength is that this study was the first to test the mediating role of psychological distress in the relation between social support and cognitive frailty among older people. The third strength is that multiple potential confounders such as socio-demographic, health behavioral (smoking and alcohol drinking), health (chronic conditions and ADL disability), and prior cognitive frailty status were controlled when examining the link between social support and cognitive frailty. Despite the strengths, our study is limited in several ways. First, the relatively small number of observations who developed cognitive frailty at the one year of follow up may cause small-sample bias. Second, the key variables (such as psychological distress) in this study, were based on self-reported data, which might lead to recall bias. Third, only one mediation variable was used in this study, and more potential paths need to be explored in the future. Finally, the current work was conducted only in rural areas, thus the results obtained from this study may be limited in urban settings, and future research should include urban areas for comparison.

Our study provides evidence that low social support is associated with increased rates of subsequent cognitive frailty among older people over 1-year follow-up. Furthermore, the effect of social support on cognitive frailty is partially mediated through psychological distress. These findings may have several important clinical and public health policy implications. First, the findings underscore the importance of screening older people at risk of cognitive frailty by assessing psychological distress. Second, the findings underline the need for clinicians to be alert to older people who report psychological distress, and it is important to help these older people getting appropriate treatment for their psychological distress. Third, social support is also important for older people to prevent cognitive frailty because it is a modifiable predictor, and improving the levels of social support is also a main way to effectively reduce psychological pressure for rural older people, such as organizing group activities and providing rural older service center.