The impact of social activities, social networks, social support and social relationships on the cognitive functioning of healthy older adults: a systematic review

Cognitive functioning plays an important role in determining functional abilities, quality of life and independence in older adults [1, 2]. Although changes in cognitive function such as processing speed, episodic memory and executive functions are typical with normative cognitive ageing [3‐5], cognitive decline is not a part of healthy ageing [6‐8]. Evidence suggests that cognitive function in older adults may be affected by modifiable risk and protective factors including smoking, poor diet, levels of physical activity, cognitive stimulation and social relationships [9‐13]. With an increasing ageing population, cognitive ageing researchers are prioritising exploration of these lifestyle factors as they may provide a pathway to interventions to prevent cognitive decline or maintain cognitive function in older adults. Of these lifestyle factors, social relationships are of particular interest as improving factors associated with social relationships may offer a relatively simple method of promoting positive outcomes in cognitive functioning.

One difficulty when trying to determine the effect of social relationships on cognitive function is the use of discrepant and unclear definitions of different social factors [14]. If researchers are to make accurate recommendations regarding activities that can promote cognitive health, they need to use precise terminology to ensure consistency and clarity of information presented. In an attempt to address the issue of discrepant definitions in the literature, Berkman and colleagues suggested a framework to clarify terms describing social factors and behaviours [15]. Berkman et al. explain that social integration, which includes upstream levels of social resources, community, and family, promotes access to social networks. Social networks, defined as “the web of social relationships that surrounds an individual” (p.847) in-turn facilitate engagement in social activities and access to social support [15]. Social relationships therefore, are both impacted by and influence social networks, social activity and social support [15‐17]. Social network characteristics can include the network size, the relationship between members of the network, and the frequency of contact between network members [15]. Examples of social activity, also known as social participation or engagement, may include meeting friends, attending events or functions, volunteering or participating in occupational duties or group recreational activities [15]. Social support, often divided into emotional, instrumental, and informational support refers to a person’s perception of the availability of help or support from others in their social network [15]. In two recent reviews, Kuiper and colleagues also refer to social relationships and explain that social networks and activity represent structural aspects of social relationships, while social support represents functional aspects of social relationships [18, 19]. In the interest of promoting the consistent use of well-defined terminology across reviews, we will use the terms as presented by Berkman et al. and Kuiper et al., and refer to the overall category of social relationships which incorporates factors including social networks, activity and support.

Research examining the effects of social relationships on older adults’ cognitive functioning most commonly assesses the frequency of engagement in social activities [20], followed by social network size/structure [21] and social support [22]. Cross-sectional studies examining the relationship between engagement in social activity and cognitive function have found that an active and socially engaged lifestyle is related to improved cognitive function in ageing [23, 24]. Results from observational studies investigating longitudinal associations between social relationships and older adults’ cognitive function are not conclusive however [25]. While many observational studies have found that aspects of social relationships, such as social activity, are related to benefits in cognitive function [9, 17, 21, 26‐29], others have failed to do so [30‐33]. The lack of consistency across observational studies is further compounded by a lack of supportive evidence from randomised controlled trials (RCTs). In their literature review, Wang et al. searched for RCTs to supplement correlational data on social activity and cognitive function, but found none, thereby limiting the extent to which causal relationships could be inferred [2]. Since then, to our knowledge, no RCTs examining lifestyle factors and cognitive function have included any social factors as primary intervention targets. Perhaps this lack of RCTs results from difficulties translating aspects of social relationships into a measurable experimental design [34]. Nonetheless, some RCTs have included engagement in social activities as active control conditions [34, 35], but these have yet to be examined in the context of a systematic review.

Consideration should be given to possible effects that different aspects of social relationships may have on specific cognitive processes [36‐38], as each unique outcome may result in differential effects on the trajectory of cognitive decline [39]. The literature has previously been criticised for not permitting an assessment of domain-specific effects of social relationships on cognition [36]. In response to this, Gow et al. examined the effects of social relationship factors on general cognitive ability, memory and processing speed and found that more social support was associated with better general cognitive abilities but not memory, and less social support was associated with slower processing speed; these associations were partly accounted for by symptoms of depression. Other studies have also reported that different aspects of social relationships can differentially impact cognitive functioning, and discrepancies between these factors can have clinically meaningful effects on cognitive function [19, 40] and incident dementia outcomes [18].

From a theoretical perspective, there is clear reason to expect an association between social relationship factors and cognitive outcomes. Social activities may include a type of cognitive stimulation, thus contributing to cognitive outcomes via the building of cognitive reserve [41]; cognitive reserve optimises cognitive performance through the recruitment of alternate brain networks and cognitive strategies to compensate for cognitive difficulties related to pathology [42, 43]. Social support in particular may impact cognitive outcomes via its buffering effect on stress [44]. Interacting with others in one’s social network may influence cognitive outcomes because close social ties makes positive health behaviours more likely (social control hypothesis; [45]). An intriguing alternative hypothesis has been put forward by Adolphs who proposes that all cognition is intrinsically social in nature [46]. It is also reasonable to assume that different aspects of social relationships may affect cognitive domains in different ways. For example, reducing stress through social support is likely to benefit memory and executive functioning [47, 48], while social network interactions may indirectly benefit reasoning, attention and processing speed through encouraging health behaviours such as exercise [12, 49]. A detailed investigated of how social relationships may affect different cognitive domains has yet to be conducted.

Few literature reviews provide a comprehensive overview of research on social relationships and cognitive function in older adults. Structural and functional aspects social relationships are not often differentiated or separately assessed [50], precluding any meaningful comment on their distinct contributions towards cognitive ageing. In addition, social factors tend to be considered alongside or as part of other lifestyle factors such as leisure or intellectual activity [41]; outcomes such as mortality, physical health, or dementia are included in lieu of cognitive function [10, 18]; only specific aspects of social relationships are considered, such as social isolation [51]; or reviews do not include comprehensive systematic literature searches [52, 53]. The findings from prior reviews have shown a positive effect of engagement in social activities on verbal fluency [53] and of ‘socialisation’ on overall cognitive function [54], but findings were inconclusive and terminology used was inconsistent. Two more recent reviews that used consistent, well-defined terminology and examined various aspects of social relationships found that poor social relationships were associated with an increased risk of cognitive decline [19] and dementia [18]. A comprehensive review has yet to be conducted that clarifies the effect of social relationships on the cognitive function (continuous outcome) of older adults.

The aim of the current review was to evaluate the association between different aspects of social relationships; specifically social activity, social networks, and social support, with the cognitive functioning of healthy older adults with no known cognitive impairment. This is the first review to include data from available RCTs and genetic (twin) studies alongside an updated summary of observational evidence. The review is also innovative in its attempt to account for the differential effects of various factors associated with social relationships on specific cognitive domains (Fig. 1).

Thirty-nine studies were identified that met the inclusion criteria outlined above; three RCTs including 576 participants, 34 observational studies including 87,509 participants in 32 longitudinal data sets, and two twin studies including 189 pairs of participants. Social activity was examined in three RCTs, 22 observational studies and two genetic studies; social networks and social support were examined in nine observational studies each, and CMSR were included in three observational studies. See Tables 1, 2, and 3. Social activity was the most common type of social relationship assessed and global/composite measures of cognitive function were the most common cognitive outcome measure employed. Overall, the type of social relationship and cognitive outcome measures included varied largely across studies (see Fig. 1).

Across the four distinct aspects of social relationships, evidence suggests a relationship between (1) social activity and global cognition, overall executive functioning, working memory, visuospatial abilities and processing speed but not episodic memory, verbal fluency, reasoning or attention; (2) social networks and global cognition but not episodic memory, attention or processing speed; (3) social support and global cognition and episodic memory but not attention or processing speed; and (4) CMSR and episodic memory and verbal fluency but not global cognition.

Researchers suggest that the size of the association between social relationships and cognition is similar to that of age and cognition [63, 72]. Our review adds to and supports existing research and findings show that there is an association between social relationships and the cognitive functioning of healthy older adults, although the specific nature of this association remains unclear. This review is novel in its examination of different aspects of social relationships, namely social activity, social networks, social support, and CMSR, and the differential effects these factors have on cognitive functioning. Evidence was most consistent in favour of a relationship between the distinct forms of social relationships and global cognition and working memory. It is important to reiterate the necessity to define social relationships more clearly to achieve homogeneity across studies [14, 40, 98]. Future research needs to achieve consistency in social and cognitive definitions and measures, replication of prior correlational findings, and the design of appropriate RCTs to provide a more thorough and meaningful investigation of the impact of social relationships on the cognitive functioning of healthy older adults.