Introduction

Advances in health technology have increased longevity. However, the rapidly raising number of aging populations caused by increased longevity has induced a lot of new challenges to overcome, which include the growing rate of age-related cognitive impairments (Graham et al., 1997; Levy, 1994; Lopez et al., 2003; Park et al., 2003; Unverzagt et al., 2001). Moreover, the rate of age-related cognitive impairments is expected to keep growing in the future (Brunner, 2005). Mild cognitive impairment is generally considered as a precursor to different types of dementias (Mitchell & Shiri-Feshki, 2009), which causes the loss of independence, disability, and ultimately mortality (Cotter, 2007; Gill et al., 1995; Phelan et al., 2012). Thus, cognitive function is an important predictor of well-being in older people, which makes it important to study its social antecedents (Berkman et al., 2000) to understand and interfere with the declines in cognitive functions in older adults.

Among social factors that contribute to cognitive functions in older adulthood, neighborhood social cohesion (NSC) has been suggested to be a significant positive predictor (Zhang et al., 2019). The definition of NSC came from Putnam’s (1995) definition of social capital which puts an emphasis on social networks, norms, trust, and reciprocity, and cohesion. Similarly, Carpiano (2006) referred it as “patterns of social interaction and values (such as network formation and ties, familiarity, and mutual trust)” (p.168). Similarly, social cohesion is defined as “neighbors’ mutual trust, solidarity, connectedness, shared values, and support” (p.228) according to Bromell and Cagney (2014). Based on these views, NSC is considered as basis of various social capital resources, and participation in neighborhood organization can be developed and used by people residing in the neighborhood (Carpiano, 2007). In summary, NSC refers to the degree of connectedness, trust, and mutual support among residents within a specific geographic community or neighborhood. NSC integrates visible neighborhood social capital (i.e., resources and services) and invisible feelings (i.e., positive experiences), which may ultimately lead to better cognitive health outcomes for neighborhood residents.

Research regarding the association between social cohesion and well-being and health can be traced back to the link found between social integration/social cohesion and mortality (Durkheim, 1897). Moreover, Sampson et al. (1997) regarded social cohesion and consequential social control as two predictors of violence rate in the community. More recently, social cohesion tends to have a positive relationship with self-rated health (Chumbler & Leech, 2013; Rios et al., 2012), mental health (Hong et al., 2014), well-being (Cramm et al., 2013; Cramm & Nieboer, 2015), but a negative association with depressive symptoms (Mair et al., 2008; Stafford et al., 2011), psychological distress (Rios et al., 2012), and mortality rates (Clark et al., 2011; Inoue et al., 2013; Lochner et al., 2003).

There are some theories that propose that social cohesion is one important predictor for cognitive functions. For instance, backed by the attention restoration theory (Berman et al., 2008; Kaplan, 1995), interacting with pleasant environments may improve attention and memory as pleasant environments help people to replenish their cognitive abilities thus enabling them to do better on tasks based on these abilities. Similarly, the cognitive reverse theory proposes how stimulating the environment can help people to develop cognitive abilities efficiently and utilize the brain to protect the brain from pathology (Tucker & Stern, 2011). Studies that have investigated the association between NSC and cognition. For instance, Lee and Waite (2018) found that NSC has a positive relationship to cognition in later life. Zhang et al. (2019) found that a positive connection between NSC and global cognitive performance, and most of its components such as the Chinese Mini-Mental State Examination, executive functions, and episodic memory in Chinese American older adults. Kang (2023; under review) found that NSC is positively associated with episodic memory in older adults.

Psychological distress could be one of the factors that explain the associations between NSC and cognitive performance. As aforementioned, social cohesion was positively associated with mental health (Hong et al., 2014), well-being (Cramm et al., 2013; Cramm & Nieboer, 2015), but negatively associated with depressive symptoms (Mair et al., 2008; Stafford et al., 2011) and psychological distress (Rios et al., 2012). Moreover, psychological distress could affect cognitive performance via psych neurological pathways. For instance, it has been suggested that distress is negatively associated with cognitive functions via dysfunctions of the hypothalamic pituitary adrenal axis (i.e., HPA; Furtado & Katzman, 2015) and changes in basal cortisol levels and diurnal rhythms (Gagnon & Wagner, 2016), which reduces the hippocampal volume and kills neurons (Lupien et al., 1998).

Thus, despite previous studies have found the associations between NSC and cognitive performance such as episodic memory and verbal fluency, much less is known about how NSC and psychological distress related to cognitive domains including fluid reasoning and verbal fluency. Moreover, it is also unclear whether psychological distress serves as a mediator of the associations between NSC and cognitive domains although there is one study suggesting that depression and anxiety symptoms mediate the positive association between NSC and episodic memory and verbal fluency respectively (Sharifian et al., 2020). Thus, the aim of the current study is to test how psychological distress could mediate the associations between NSC and cognitive performance including verbal semantic fluency, fluid reasoning, and verbal fluency in older adults from the UK.

Methods

Data

The current research extracted and analyzed data from Wave 3 (collected between 2010 and 2011), Understanding Society: the UK Household Longitudinal Study (University of Essex, 2022). All data collections followed relevant guidelines and regulations and were approved by the University of Essex. Participants who were younger than 55 years old or had any missing variables of interest were removed. Thus, there were 4922 older adults with a mean age of 66.51 (S.D. = 8.27) years old and 47.01% males remained.

Measures

NSC

NSC was measured using 4 items including (1) “This is a close-knit neighborhood.” (2) “People around here are willing to help their neighbors.” (3) People in this neighborhood can be trusted. (4) “People in this neighborhood generally don't get along with each other.” on a 5-point Likert scale ranging from 1 (“Strong agree”) to 5 (“Strong disagree”). Items 1, 2, and 3 were reverse coded (Cagney et al., 2009; Sharifian et al., 2020; Zhang et al., 2019). The standardized summary score of these items was used for further analysis. The internet consistency of these items is 0.8.

Psychological distress

Psychological distress was measured using the GHQ-12 with response ranging from 0 (“Not at all”) to 3 (“Much more than usual”; Goldberg & Williams, 1988). A standardized summary score across all the 12 items was used. Specifically, a higher GHQ-12 summary score means more psychological distress.

Cognitive abilities

An immediate and a delayed word recall tasks were used to assess episodic memory. An animal fluency task was used to assess semantic verbal fluency (Fisher et al., 2013; Henry et al., 2004; Rosen, 1980). The number series task was designed to test fluid reasoning, which is the ability to use abstract thought to solve novel problems. Fluid reasoning ability is typically assessed via logic puzzles (Fisher et al., 2013). Numerical ability tests involve solving problems that might be encountered in daily life, which was measured by a series of question such as “In a sale, a shop is selling all items at half price. Before the sale, a sofa costs £300. How much will it cost in the sale?” Details of the procedures of these tasks can be found in https://www.understandingsociety.ac.uk/sites/default/files/downloads/documentation/mainstage/user-guides/6614_Cognitive_Ability_measures_v1.1.pdf. All scores were standardized before further analysis.

Study controls

Study controls included age, sex, monthly income, education, and marital status. Please refer to Table 1 for how these items were coded in the model.

Table 1 Descriptive statistics of demographic characteristics, NSC, psychological distress, and cognitive performance
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Analysis

The current study used multiple regression models to establish the connections between NSC and cognitive performance, NSC and psychological distress, and psychological distress and episodic cognitive performance. Specifically, study controls including age, sex, income (monthly), education, and marital status and NSC were taken into four regression models as predictors with episodic memory, semantic verbal fluency, fluid reasoning, and numeracy as the predicted variable respectively. The predictors in the fifth model included study controls including age, sex, income (monthly), education, and the marital status and NSC with psychological distress as measured by the GHQ-12 as the predicted variable. Finally, predictors in the final four models included controls consisting of age, sex, monthly income, education, and marital status and psychological distress, and the predicted variables included episodic memory, semantic verbal fluency, fluid reasoning, and numeracy respectively.

To test whether psychological distress serves as a mediator for the association between NSC and cognitive abilities based on interpreting the results from the multiple regressions, mediation analyses were performed by the mediation toolbox on MATLAB 2018a with 10000 bootstrap sample significance testing with demographics including age, sex, income (monthly), education, and marital status as covariates (https://github.com/canlab/MediationToolbox).

Results

Table 1 demonstrated the descriptive statistics. The current study found that NSC is positively related to episodic memory (b = 0.04, p < 0.01, 95% C.I. [0.02, 0.07]), semantic verbal fluency (b = 0.03, p < 0.05, 95% C.I. [0.01, 0.06]), fluid reasoning (b = 0.03, p < 0.05, 95% C.I. [0.01, 0.06]), and numeracy (b = 0.05, p < 0.001, 95% C.I. [0.03, 0.07]; Table 2), but negatively related to psychological distress (b = -0.11, p < 0.001, 95% C.I. [-0.14, -0.09]; Table 3). Moreover, psychological distress was negatively related to episodic memory (b = -0.07, p < 0.001, 95% C.I. [-0.10, -0.05]), semantic verbal fluency (b = -0.07, p < 0.001, 95% C.I. [-0.10, -0.04]), fluid reasoning (b = -0.07, p < 0.001, 95% C.I. [-0.10, -0.04]), numeracy (b = -0.06, p < 0.001, 95% C.I. [-0.08, -0.03]; Table 4).

Table 2 NSC predicts cognitive performance
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Table 3 NSC predicts psychological distress
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Table 4 Psychological distress predicts cognitive performance
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Mediation analysis showed a significant effect of Path a (i.e., NSC to psychological distress; b = -0.11, p < 0.001, 95% C.I. [-0.12, -0.10]), Path b (psychological distress to episodic memory; b = -0.07, p < 0.001, 95% C.I. [-0.08, -0.06]), Path c (total effect; b = 0.04, p < 0.01, 95% C.I. [0.03, 0.05]), Path c' (direct effect; b = 0.03, p < 0.05, 95% C.I. [0.02, 0.04]), and Path a*b (mediation effect; b = 0.01, p < 0.001, 95% C.I. [0.01, 0.01]), which indicated a partial mediation. Similarly, there was a significant effect of Path a (i.e., NSC to psychological distress; b = -0.11, p < 0.001, 95% C.I. [-0.12, -0.10]), Path b (psychological distress to semantic verbal fluency; b = -0.07, p < 0.001, 95% C.I. [-0.08, -0.06]), Path c (total effect; b = 0.03, p < 0.05, 95% C.I. [0.03, 0.04]), and Path a*b (mediation effect; b = 0.01, p < 0.001, 95% C.I. [0.01, 0.01]). However, the effect of Path c' (direct effect) was not significant, which indicated a complete mediation. Moreover, there was a significant effect of Path a (i.e., NSC to psychological distress; b = -0.11, p < 0.001, 95% C.I. [-0.12, -0.10]), Path b (psychological distress to fluid reasoning; b = -0.07, p < 0.001, 95% C.I. [-0.08, -0.06]), Path c (total effect; b = 0.03, p < 0.05, 95% C.I. [0.02, 0.04]), and Path a*b (mediation effect; b = 0.01, p < 0.001, 95% C.I. [0.01, 0.01]). However, the effect of Path c' (direct effect) was not significant, which indicated a complete mediation. Finally, there was a significant effect of Path a (i.e., NSC to psychological distress; b = -0.11, p < 0.001, 95% C.I. [-0.12, -0.10]), Path b (psychological distress to numeracy; b = -0.07, p < 0.001, 95% C.I. [-0.08, -0.06]), Path c (total effect; b = 0.04, p < 0.01, 95% C.I. [0.03, 0.05]), Path c' (direct effect; b = 0.03, p < 0.05, 95% C.I. [0.02, 0.04]), and Path a*b (mediation effect; b = 0.01, p < 0.001, 95% C.I. [0.01, 0.01]), which indicated a partial mediation. The results from the mediation analyses can be found in Table 5 and Fig. 1.

Table 5 Coefficient, standard error, t value, Z score, 95% confidence interval, and associated p-value output from the mediation toolbox with NSC as the predictor, psychological distress as the mediator, and cognitive performance including episodic memory, semantic verbal fluency, fluid reasoning, and numeracy the predicted variables respectively
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Fig. 1
figure 1figure 1

Path diagrams that show significant Path a (i.e., NSC to psychological distress), Path b (psychological distress to cognitive performance), Path c (total effect), Path c' (direct effect), and Path a*b (mediation effect). The unstandardized path coefficients are shown in the image with their standard errors. * p < 0.05, ** p < 0.01, *** p < 0.001

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Discussion

The current research aimed to test whether psychological distress mediates the associations between NSC and cognitive performance including episodic memory, semantic verbal fluency, fluid reasoning, and numeracy in 4922 older adults with a mean age of 66.51 (S.D. = 8.27) years old and 47.01% males from Understanding Society. Results revealed that NSC has a positive relationship to all cognitive measures but a negative association with psychological distress, whereas psychological distress is negatively associated with all cognitive performance. Moreover, there was a complete mediation effect of psychological distress on the positive relationship between NSC and semantic verbal fluency and the association between NSC and fluid reasoning. However, NSC only partially mediated the positive associations between NSC and episodic memory and numeracy respectively. The current study is one of the few studies that understood the effect of NSC in cognitive functions in older adults from the UK. Results from the current study may provide additional evidence regarding the notion that neighborhood social characteristics have a higher chance to offer a good source of “cognitive reserve” (Clarke et al., 2012, p. 730). Moreover, the current study identified psychological distress as a potential pathway that explains this relationship.

The current study found that NSC is positively associated with all cognitive measures, which seems to be consistent with several previous research (Lee & Waite, 2018; Sharifian et al., 2020; Zhang et al., 2019). Besides the widely examined associations between NSC and episodic memory and semantic verbal fluency, the current study adds to the literature by demonstrating that NSC is also positively related to fluid reasoning and numeracy, which are important but less investigated cognitive abilities that play a significant role in older adults’ life. Moreover, the current study found that psychological distress is negatively associated with all cognitive measures, which adds to the literature regarding the less studied associations between psychological distress and cognitive performance, especially in fluid reasoning and numeracy.

Importantly, the current study found that psychological distress mediates the association between NSC and all cognitive measures. Via the trust and shared values in the neighborhood context, residents in the neighborhood may increase the expectations that they can together achieve common goals (Sampson, 2003). Thus, a healthy lifestyle can be promoted through collective efforts including actions such as protecting safe public space, providing clean and safe housing, and promoting nutritional foods (Rois et al., 2012). Socially cohesive neighborhoods can also provide a belonging of community which can contribute to the affective component of social cohesion that can reduce psychological distress (Rois et al., 2012). Reduced psychological distress then may in turn promote cognitive abilities through neuropsychological pathways. Specifically, exposure to long-term exposure to glucocorticoids caused by psychological distress could lead to the reduction of pyramidal neurons in the frontal, pre/postcentral, and cingulate gyri, and the hippocampus of nonhuman primates (Sapolsky et al., 1990). Moreover, psychological distress can also negatively affect cognition by inducing abnormal changes in basal cortisol levels and diurnal rhythms (Gagnon & Wagner, 2016), which reduces the hippocampal volume and kills neurons (Lupien et al., 1998). The evidence regarding the neurophysiological association between psychological distress and cognition can be found in patients with various neurological conditions. For instance, people with chronic distress such as posttraumatic stress disorder (PTSD) often showed long-term cognitive impairments. In addition, patients with Cushing’s syndrome and depression with high basal cortisol levels have reduced hippocampal volume and thus have impaired cognition (De Kloet et al., 2005; Sheline et al., 1996; Starkman et al., 1992).

The finding that psychological distress completely mediates the associations between NSC and semantic verbal fluency, as well as NSC and fluid reasoning, suggests that the relationship between these variables is fully explained by the presence of psychological distress. On the other hand, the finding that psychological distress partially mediates the associations between NSC and episodic memory, as well as NSC and numeracy, suggests that psychological distress plays a role in explaining these associations, but it is not the sole factor involved. In these cases, there may be additional factors or mechanisms at play that influence the relationship between NSC and episodic memory or numeracy. One potential explanation for this inconsistency is that these distinct cognitive abilities rely on separate neural networks, which exhibit varying levels of resilience to the impact of psychological distress (De Kloet et al., 2005; Sheline et al., 1996; Starkman et al., 1992).

Despite this study’s strength, there are a couple of limitations of this study as well. First, the current study focused on older adults living in the UK, which may make it hard to generate findings from the current study to people in other age groups and people living in other countries. Future studies in other settings should be conducted to strengthen the external validity of the current findings. Second, the current study relied on cross-sectional data, which makes the current study to rule out reciprocal causation. Third, the current study found that psychological distress fully partially mediates the associations between NSC and semantic verbal fluency and fluid reasoning but partially mediates the associations between NSC and episodic memory and numeracy, which may indicate the potential pathways of NSC and episodic memory and numeracy are not fully explained. For instance, as concluded by Seeman et al. (2011), the effects of NSC on cognition may go through other “biological and physiological pathways such as reduced physiological reactivity, lower levels of physiological arousal, and direct positive stimulation”. Future studies should test how these pathways could explain the relationship between NSC and cognitive performance.

Taken together, the current study examined how psychological distress could mediate the association between NSC and cognitive abilities including episodic memory, semantic verbal fluency, fluid reasoning, and numeracy, and found that psychological distress significantly mediates the association between NSC and cognitive performance. Implications can be drawn from results of the current study. For instance, from a policy standpoint, findings from the current study contribute the evidence that reinforces program designers and policy makers to join the WHO’s (WHO, 2007) global efforts to construct age-friendly communities (Zhang et al., 2019), which promotes NSC, then leads to reduced psychological distress, and thus better cognitive functions among the elderly. Preserving cognitive functions may in turn reduce health care burdens.