Social isolation is linked to alterations in brain structure and cognitive deficits


Why do we get a buzz from being in large groups at festivals, jubilees and other public events?

According to the social brain hypothesis, it’s because the human brain specifically evolved to support social interactions. Studies have shown that belonging to a group can lead to improved wellbeing and increased satisfaction with life.

Unfortunately though, many people are lonely or socially isolated. And if the human brain really did evolve for social interaction, we should expect this to affect it significantly. Our recent study, published in Neurology, shows that social isolation is linked to changes in brain structure and cognition – the mental process of acquiring knowledge – it even carries an increased risk of dementia in older adults.

There’s already a lot of evidence in support of the social brain hypothesis. One study mapped the brain regions associated with social interaction in approximately 7,000 people.

It showed that brain regions consistently involved in diverse social interactions are strongly linked to networks that support cognition, including the default mode network (which is active when we are not focusing on the outside world), the salience network (which helps us select what we pay attention to), the subcortical network (involved in memory, emotion and motivation) and the central executive network (which enables us to regulate our emotions).

We wanted to look more closely at how social isolation affects grey matter – brain regions in the outer layer of the brain, consisting of neurons. We, therefore, investigated data from nearly 500,000 people from the UK Biobank, with a mean age of 57. People were classified as socially isolated if they were living alone, had social contact less than monthly and participated in social activities less than weekly.

Our study also included neuroimaging (MRI) data from approximately 32,000 people. This showed that socially isolated people had poorer cognition, including in memory and reaction time, and lower volume of grey matter in many parts of the brain.

These areas included the temporal region (which processes sounds and helps encode memory), the frontal lobe (which is involved in attention, planning and complex cognitive tasks) and the hippocampus – a key area involved in learning and memory, which is typically disrupted early in Alzheimer’s disease.

We also found a link between the lower grey matter volumes and specific genetic processes that are involved in Alzheimer’s disease.

There were follow-ups with participants 12 years later. This showed that those who were socially isolated, but not lonely, had a 26% increased risk of dementia.

Underlying processes
Social isolation needs to be examined in more detail in future studies to determine the exact mechanisms behind its profound effects on our brains. But it is clear that, if you are isolated, you may be suffering from chronic stress. This in turn has a major impact on your brain, and also on your physical health.

Another factor may be that if we don’t use certain brain areas, we lose some of their function. A study with taxi drivers showed that the more they memorised routes and addresses, the more the volume of the hippocampus increased. It is possible that if we don’t regularly engage in social discussion, for example, our use of language and other cognitive processes, such as attention and memory, will diminish.

This may affect our ability to do many complex cognitive tasks – memory and attention are crucial to complex cognitive thinking in general.

Tackling loneliness
We know that a strong set of thinking abilities throughout life, called “cognitive reserve”, can be built up through keeping your brain active. A good way to do this is by learning new things, such as another language or a musical instrument.

Cognitive reserve has been shown to ameliorate the course and severity of aging. For example, it can protect against a number of illnesses or mental health disorders, including forms of dementia, schizophrenia and depression, especially following traumatic brain injury.

There are also lifestyle elements that can improve your cognition and wellbeing, which include a healthy diet and exercise. For Alzheimer’s disease, there are a few pharmacological treatments, but the efficacy of these need to be improved and side effects need to be reduced.

There is hope that in the future there will be better treatments for aging and dementia. One avenue of inquiry in this regard is exogenous ketones – an alternative energy source to glucose – which can be ingested via nutritional supplements.

But as our study shows, tackling social isolation could also help, particularly in old age. Health authorities should do more to check on who is isolated and arrange social activities to help them.

When people are not in a position to interact in person, technology may provide a substitute. However, this may be more applicable to younger generations who are familiar with using technology to communicate. But with training, it may also be effective in reducing social isolation in older adults.

Social interaction is hugely important. One study found that the size of our social group is actually associated with the volume of the orbitofrontal cortex (involved in social cognition and emotion).

But how many friends do we need? Researchers often refer to “Dunbar’s number” to describe the size of social groups, finding that we are not able to maintain more than 150 relationships and only typically manage five close relationships.

However, there are some reports which suggest a lack of empirical evidence surrounding Dunbar’s number and further research into the optimal size of social groups is required.

It is hard to argue with the fact that humans are social animals and gain enjoyment from connecting with others, whatever age we are. But, as we are increasingly uncovering, it also crucial for the health of our cognition.

Loneliness and social isolation have separate and distinct definitions; however, in some instances, the terms can be found used interchangeably and as a proxy for one another in published commentaries and research studies. Loneliness is typically defined as the subjective state of a person’s desired and actual relationships and a measure of relationship quality (Cacioppo et al., 2002; Cornwell & Waite, 2009; Musich et al., 2015; Ong et al., 2016). In contrast, social isolation is an objective count of relationships, social interactions, and social contacts, determined by their quantity and sometimes quality (Cudjoe et al., 2020; MacLeod et al., 2018). While these constructs can overlap, not all assessment, evaluation, and intervention approaches work universally for these constructs; thus, they should be considered differently yet relative to one another (NASEM 2020).

Previous studies indicate up to 55% of US older adults age 65 years or older report some level of loneliness (Musich et al., 2015; Perissinotto et al., 2012). Meanwhile, social isolation is estimated to impact up to 40% of older adults age 60 and older (Cudjoe et al., 2020; MacLeod et al., 2018). Furthermore, current evidence suggests that many older adults are either socially isolated, lonely, or both, which can put their health at risk in many ways (Courtin & Knapp, 2017). Recently, the AARP Foundation commissioned a committee through the National Academies of Science, Engineering and Medicine (NASEM) to examine the current science and future directions of loneliness and social isolation in older adults. Their consensus 2020 report highlights many risk factors that are associated with loneliness and social isolation including social, cultural, and environmental factors (e.g. age, gender, housing, location, living alone), psychological and cognitive factors (e.g. depression, anxiety, impairment), and physical health factors (e.g. health status, presence of chronic diseases, and limited function). In addition, many associated health outcomes have been associated with the two constructs including cardiovascular disease, stroke, dementia, and mortality (NASEM 2020).

An adaptation of the NASEM guiding framework of loneliness and social isolation is shown in Figure 1. Overall, the theoretical framework demonstrates that there is a bidirectional relationship between loneliness and social isolation under the umbrella term social connection (Holt-Lunstad et al., 2017) as well as a relationship with pre-existing risk factors, and specific health outcomes (Donovan & Blazer, 2020; NASEM 2020). As mentioned, previous studies have demonstrated that loneliness and social isolation are both independently associated with similar negative physical and mental health outcomes later in life including higher rates of mortality, depression, and cognitive decline (Beutel et al., 2017; Drageset et al., 2013; Holt-Lunstad et al., 2010; 2015; 2017; Kelly et al., 2017; Kuiper et al., 2015; Luo & Waite, 2014; Musich et al., 2015; Ong et al., 2016; Perissinotto et al., 2012). However, most of these studies examined the two constructs independently of each other.

Figure 1. Theoretical framework of loneliness, social isolation, and associated health outcomes.

Note. Adaptation of guiding framework developed by the Committee on the Health and Medical Dimensions of Social Isolation and Loneliness in Older Adults 2020 (NASEM 2020).

Figure 1 of 2
Figure 1. Theoretical framework of loneliness, social isolation, and associated health outcomes.
Note. Adaptation of guiding framework developed by the Committee on the Health and Medical Dimensions of Social Isolation and Loneliness in Older Adults 2020 (NASEM 2020).
Figure 2 of 2
Figure 2. Distribution of loneliness and social isolation in our sample of older adults (N = 6,994). Note: 60.5% were Neither (n = 4,232)

For instance, loneliness has shown independent associations with depression, poor sleep, hypertension, cognitive decline, and other poor health outcomes (Hackett et al., 2012; Hawkley et al., 2010; MacLeod et al., 2018; Musich et al., 2015; Perissinotto et al., 2012Perissinotto, C. M., Stojacic Cenzer, I., & Covinsky, K. E. (2012). Loneliness in older persons: A predictor of functional decline and death. Arch Intern Med, 72, 1078–1084.
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; Steptoe et al., 2004). Meanwhile, social isolation has been associated with increased cardiovascular disease, inflammatory processes, increased dementia risk, disability, cognitive decline, mortality, and reduced quality of life (QOL) in independent analyses (Barth et al., 2010; Bassuk et al., 1999; Grant et al., 2009; Heffner et al., 2011; Shankar et al., 2011; Steptoe et al., 2013). In addition, social isolation puts older adults at an increased risk for loneliness (Dickens et al., 2011; MacLeod et al., 2018; Masi et al., 2011).

Despite the awareness of loneliness and social isolation as serious independent health risks, the combined and cumulative impact of these constructs has not been studied extensively. A handful of studies have attempted to examine both loneliness and social isolation in the same analyses (Beller & Wagner, 2018a, 2018b; Donovan et al., 2017; Hakulinen et al., 2018; Holwerda et al., 2014; Ong et al., 2016; Shankar et al., 2013; Steptoe et al., 2013; Wilson et al., 2007). Specifically, these studies have primarily modeled both loneliness and social isolation as separate predictors of various health outcomes but have not examined their cumulative effect. For instance, Steptoe et. al found that social isolation remained the strongest predictor of mortality as compared to loneliness when modeled together (Steptoe et al., 2013). To our knowledge, no study has examined the impact of having both loneliness and social isolation as a predictor variable.

Elsewhere, researchers have found that reduced QOL, increased healthcare utilization, and overall higher medical costs can be attributed to loneliness and social isolation in joint analyses (Gerst-Emerson & Jayawardhana, 2015; Greysen et al., 2013; Hawker & Romero-Ortuno, 2016; Jakobsson et al., 2011; Shaw et al., 2017; Valtorta et al., 2018). Nevertheless, research exploring the outcomes of older individuals experiencing concurrent loneliness and social isolation remains limited. It’s been suggested that the health risks associated with loneliness and isolation are equivalent to the well-established detrimental effects of smoking and obesity (Holt-Lunstad et al., 2010). Furthermore, loneliness and social isolation are particularly problematic in old age due to decreasing economic and social resources, functional limitations, the death of relatives and spouses, and changes in family structures and mobility (Courtin & Knapp, 2017). Thus, interventions that promote improving social connectedness and eliminating social barriers could be extremely important in improving outcomes in older adults including promoting active aging (Stathi et al., 2020).

With this in mind, the purpose of this study was to examine loneliness and social isolation in a large older adult population, and to serve as one of the first studies to examine both constructs in a cumulative manner. Specifically, this study aimed to 1) describe the overlap between loneliness and social isolation by identifying those who are both lonely and socially isolated, lonely only, socially isolated only, or neither; and 2) examine the cumulative effect of loneliness and social isolation on various health outcomes. Outcomes of interest included QOL, healthcare utilization and medical costs. Based on the research literature, we hypothesized that study participants who were both lonely and socially isolated would be more likely to be older, female, with poorer health and greater risk factors compared to adults who were only lonely, socially isolated, or neither. In addition, study participants who were both lonely and socially isolated would be more likely to have lower QOL, higher healthcare utilization, and higher medical costs.

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Source: The Conversation


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