Loneliness and Health
- Aparna ShankarAparna ShankarDepartment of Behavioural Medicine, University of London
Loneliness or perceived social isolation is a subjective experience relating to dissatisfaction with one’s social relationships. Most research has focused on the experience of loneliness in old age, but levels of loneliness are also known to be high among teenagers and young adults. While poor health may be associated with increased feelings of loneliness, there is now considerable evidence on the role of loneliness as a risk factor for poor mental and physical health. Studies show that loneliness is associated with an increased risk of developing dementia and chronic diseases, and also with a higher rate of mortality. Risky health behaviors, a poor cardiovascular profile and compromised immune functioning have all been proposed as potential pathways through which loneliness may affect health. However, much still remains to be understood about these mechanisms.
Loneliness refers to dissatisfaction with one’s personal relationships. Often termed as “perceived social isolation,” loneliness can be distinguished from “objective” isolation measures such as living arrangements, social contact, or social engagement. Feelings of loneliness involve a subjective evaluation related to a person’s expectations of and satisfaction with the frequency and closeness of contacts (de Jong Gierveld & Havens, 2004), and the perception of a discrepancy between available and desired social connections (Peplau & Perlman, 1982). It is, therefore, possible to be socially connected and experience feelings of loneliness (J. T. Cacioppo, Cacioppo, Cole, et al., 2015; J. T. Cacioppo et al., 2000; Cornwell & Waite, 2009). Feelings of loneliness are unpleasant and distressing (Peplau & Perlman, 1982). All individuals experience loneliness at some point, and in most cases this is a transient state. Indeed, feelings of loneliness may even play an adaptive role by prompting a person to take steps to alleviate such feelings by trying to build closer relationships with others (J. T. Cacioppo et al., 2006; Hawkley & Cacioppo, 2010; Hawkley & Capitanio, 2015; Peplau & Perlman, 1982; Weiss, 1973). However, for some people the experience of loneliness is severe and persistent. This chronic loneliness is particularly damaging to mental and physical health (Hawkley & Cacioppo, 2010).
Loneliness Across the Life Course
While loneliness is often portrayed as a phenomenon that is unique to older age, it can be experienced across the life course. Loneliness shows a U-shaped relationship with age, being particularly high in adolescence and in later life (Dykstra, 2009; Victor & Yang, 2012). Evidence from twin studies suggests that up to 50% of the variance in loneliness may be heritable (Bartels, Cacioppo, Hudziak, & Boomsma, 2008; Boomsma, Willemsen, Dolan, Hawkley, & Cacioppo, 2005; McGuire & Clifford, 2000). A genome-wide association study of loneliness using data from adults aged 50 years and over, however, showed much lower estimates of heritability (14%–27%) (Gao et al., 2017). While some studies have not found any age-related differences in the genetic architecture of loneliness (Boomsma et al., 2005; McGuire & Clifford, 2000), Bartels et al. in their longitudinal study of twins from age 7 to age 12 years found that the influence of genetic factors decreased while that of environmental factors increased with age (Bartels et al., 2008).
The reasons why people experience feelings of isolation vary across the life course in line with developmental changes and social needs (Peplau & Perlman, 1982; Qualter et al., 2015). For young children, it is important to have a large network of friends. As they grow up, more value is placed on closeness in friendships, which leads to a greater emphasis on the quality of relationships. Being accepted by one’s peer group is also important in later childhood and adolescence. Romantic relationships play an important part in adolescence and adulthood, and a lack of intimate relationships may lead to feelings of loneliness at this stage of life (Peplau & Perlman, 1982; Qualter et al., 2015). In later life, widowhood, poor health, disability, and a loss of independence are all associated with feelings of loneliness (J. T. Cacioppo, Cacioppo, Cole, et al., 2015; Hawkley et al., 2008; Qualter et al., 2015).
Demographic and Cultural Determinants
Socioeconomic status is an important predictor of loneliness, and individuals who are more socioeconomically disadvantaged, unemployed, or have low education levels often report high levels of loneliness (Bosma, Jansen, Schefman, Hajema, & Feron, 2015; Hawkley et al., 2008; Lasgaard & Friis, 2015; Pinquart & Sorensen, 2001). While several studies find that women report higher levels of loneliness when compared with men, it has been suggested that this may actually depend on the way the construct is measured (Pinquart & Sorensen, 2001). Cultural factors also play an important role in the experience of loneliness (Peplau & Perlman, 1982), and the prevalence of loneliness varies across countries (Abdallah, Stoll, & Eiffe, 2013; de Jong Gierveld & Havens, 2004; de Jong Gierveld, Keating, & Fast, 2015; Pinquart & Sorensen, 2001). Loneliness is believed to be higher in individualistic societies than in collectivist societies. However, using data from several European countries, Dykstra (2009) notes that the prevalence of loneliness is actually higher among older adults in South European countries such as Greece and Portugal, which are typically characterized by stronger social and familial ties, compared with many Scandinavian countries. This trend may be related to the expectations that people in collectivist societies hold regarding aging, and one’s relationships with children and grandchildren. Much of the work on loneliness has been carried out in North America and Europe, and there are limited data on prevalence and risk factors for loneliness in other countries. For instance, available data from countries of the former Soviet Union suggest very high levels of loneliness in some of these countries, particularly among older adults (Stickley et al., 2013). Further work is warranted in this area to better understand social and cultural influences on the experience of loneliness.
Changing family patterns and the growing number of individuals who live alone have led to concerns regarding an increase in the prevalence of loneliness. Some researchers have, however, suggested that these concerns may be unfounded (Dykstra, 2009). Longitudinal studies conducted in the Netherlands found little change in loneliness among older adults at the population level (Honigh-de Vlaming, Haveman-Nies, Bos-Oude Groeniger, de Groot, & van ’t Veer, 2014; Tijhuis, De Jong-Gierveld, Feskens, & Kromhout, 1999). Data from cross-sectional surveys suggest that the prevalence among older adults in the United Kingdom has been relatively steady since the 1940s at approximately 10% (Victor, 2016). Demographic shifts with an increase in the aging population, however, mean a possible increase in the absolute numbers of older adults who may suffer from loneliness. It must also be noted that there may be differences in methodologies and scales used across different studies, rendering comparisons difficult.
A number of chronic conditions bring with them pain, problems with mobility, distressing symptoms, and a range of other challenges. Such conditions may be extremely isolating and lead to feelings of loneliness (Barageine et al., 2015; Barlow, Liu, & Wrosch, 2015; Burholt & Scharf, 2014; Deckx, van den Akker, & Buntinx, 2014; Theeke & Mallow, 2013). Studies show that among individuals with chronic health conditions, feelings of loneliness may also serve to exacerbate existing symptoms. Wolf et al. found daily fluctuations in loneliness associated with worsening pain among fibromyalgia patients (Wolf & Davis, 2014; Wolf, Davis, Yeung, & Tennen, 2015). These authors found that feelings of loneliness were associated with more negative thoughts about pain among patients, which in turn led to increased experiences of pain (Wolf et al., 2015). Among cancer patients and older dementia caregivers, loneliness was found to be associated with an increased risk of a symptom cluster of pain, depression, and fatigue (Jaremka, Andridge et al., 2014). Several studies have focused on loneliness as a specific risk factor for ill health and mortality. The following section reviews some of the evidence in this area.
Morbidity and Mortality
A lack of social relationships has been associated with an increased risk of mortality, comparable to traditional risk factors such as being overweight or smoking (Holt-Lunstad, Smith, & Layton, 2010). A meta-analysis comparing the effects of objective isolation and loneliness suggests that both have an effect on mortality, with similar effect sizes (Holt-Lunstad, Smith, Baker, Harris, & Stephenson, 2015). Most studies examining mortality or other health outcomes, however, fail to examine both isolation and loneliness in conjunction. Of the two studies that do examine isolation and loneliness together in relation to mortality, one found that objective isolation but not loneliness was associated with mortality following adjustment (Steptoe, Shankar, Demakakos, & Wardle, 2013), while the other found the reverse (Holwerda et al., 2012).
A meta-analysis of 3 studies found that loneliness was associated with a nearly 30% increase in incident coronary heart disease (Valtorta, Kanaan, Gilbody, Ronzi, & Hanratty, 2016). As loneliness is often identified as an issue that is particularly pertinent to older adults, many studies have examined it as a risk factor for outcomes that are important to aging populations. These include outcomes such as declines in physical function, disability and frailty. Studies have found that loneliness is related to declines in motor function among older adults (Buchman et al., 2010; Shankar, McMunn, Demakakos, Hamer, & Steptoe, 2017), although findings with regard to reported increases in difficulties with basic daily activities such as dressing oneself, bathing and getting around are mixed (Perissinotto, Cenzer, & Covinsky, 2012; Shankar et al., 2017; Stessman, Rottenberg, Shimshilashvili, Ein-Mor, & Jacobs, 2014). In a cross-sectional analyses, loneliness was also found to be associated with frailty (defined as meeting at least three of the following criteria weight loss, exhaustion, low physical activity, slowness, or weakness) among community-dwelling Mexicans aged 70 years and older (Herrera-Badilla, Navarrete-Reyes, Amieva, & Avila-Funes, 2015) and urinary incontinence (Ramage-Morin & Gilmour, 2013).
Cognitive Function and Dementia
As with the studies of functional decline and frailty, there has been a growing interest in the role of social relationships in cognitive decline and dementia. Interactions with others are believed to contribute to building cognitive reserve (Fratiglioni, Wang, Ericsson, Maytan, & Winblad, 2000), thus protecting against deterioration in cognitive function as one ages, even in the presence of pathological brain changes. In their review of studies of loneliness and cognitive function, Boss et al. found that half the published studies were cross sectional, making it difficult to disentangle whether loneliness is a cause or consequence of declining cognitive function. Of the five longitudinal studies, two found that loneliness was associated with incident Alzheimer’s disease/dementia, one found that loneliness was associated with declining cognitive function after 10 years, and two found loneliness to be associated with declines in memory. No significant associations were found with executive function (Boss, Kang, & Branson, 2015). Kuiper et al. (2015), in their meta-analysis of three studies, found that loneliness was associated with a nearly 60% increase in the risk of incident dementia. Overall, however, the evidence for social relationships as a risk factor for cognitive decline remains poor (Baumgart et al., 2015), as studies often are unable to determine whether changes seen in cognitive decline are clinically significant. Hence, more longitudinal studies using larger samples with better measures of loneliness, using standardized assessments of cognitive function and dementia, and adjusting for important covariates and are necessary.
Furthermore, bidirectional associations between loneliness and cognitive decline are possible. Marked declines in cognitive ability are distressing, and can cause the sufferer to withdraw from social contact. Others may also feel unsure about how to interact with someone who has known cognitive difficulties (Ayalon et al., 2016). Hence, changes in functioning may lead to greater isolation and loneliness. A few studies have examined the bidirectional associations between loneliness and cognitive function. Two studies found stronger associations between cognitive function measures and later loneliness than vice versa (Ayalon, Shiovitz-Ezra, & Roziner, 2016; Zhong, Chen, Tu, & Conwell, 2016), while others have found that the reverse is true (Donovan et al., 2016; Wilson, Krueger, Arnold, & et al., 2007).
Loneliness and depression are often thought of as being the same. Indeed scales such as the Centre for Epidemiologic Studies Depression scale include “feeling lonely” as one of the symptoms of depression (Radloff, 1977). A genome-wide association study also found some evidence in support of the co-heritability of loneliness and depressive symptoms (Gao et al., 2017). However, studies have identified depression and loneliness as distinct constructs (J. T. Cacioppo et al., 2006; VanderWeele, Hawkley, Thisted, & Cacioppo, 2011; Weeks, Michela, Peplau, & Bragg, 1980). Indeed, feelings of loneliness are an important predictor of future incidence and severity of depression (J. T. Cacioppo, Hawkley, & Thisted, 2010; Holvast et al., 2015). It has also been suggested that depression may be a pathway through which loneliness can affect health (S. Cacioppo, Capitanio, & Cacioppo, 2014). Data from the Longitudinal Aging Study Amsterdam found that depression was a strong predictor of mortality among lonely men, suggesting that loneliness and depression in combination is particularly harmful for health (Holwerda et al., 2016).
Research with respect to other mental health conditions is largely cross-sectional in nature. Feelings of loneliness are common among individuals diagnosed with psychotic and mood disorders (Badcock et al., 2015; Giacco, Palumbo, Strappelli, Catapano, & Priebe, 2016; Sündermann, Onwumere, Kane, Morgan, & Kuipers, 2014). Świtaj et al. found that loneliness mediates the relationship between stigma and depressive symptoms among people with major psychiatric conditions (Świtaj, Grygiel, Anczewska, & Wciórka, 2014; Świtaj, Grygiel, Anczewska, & Wciórka, 2015). Loneliness is associated with the use of psychotropic drugs (Boehlen et al., 2015; Canham, 2015), independent of depressive symptoms and symptom severity (Boehlen et al., 2015). Loneliness was also identified as a potential mediator of the association between emotional dysregulation and the psychopathology associated with binge eating and bulimia nervosa (Southward et al., 2014). However, the cross-sectional designs of these studies make it difficult to determine whether loneliness is a risk factor for these mental health conditions or is an outcome, given what is known about isolation and stigma following diagnosis of a mental health condition (Alonso et al., 2009). Further, individuals with certain mental health conditions may suffer from symptoms that make it more difficult to develop and sustain close social networks (Anderson, Laxhman, & Priebe, 2015), leading to feelings of loneliness.
There are several reasons why individuals who are lonely may be more likely to have poorer health behaviors. The social control hypothesis (House, 2001) suggests that individuals who are lonely may be more prone to unhealthy practices due to limited access to social support and social cues that promote healthy behaviors. Another reason why loneliness may lead to risky health behavior is because lonely individuals are less likely to use active coping strategies when faced with stressful situations. Hence, their response to feeling or loneliness or other stressors may be through sad passivity (Rubenstein, Shaver, & Peplau, 1979), resorting to risky behaviors such as smoking, drinking to excess, or taking drugs. Another explanation suggests that feelings of loneliness lead individuals to be hypervigilant to social threats, thereby limiting the resources available to them for self-regulation (Hawkley & Cacioppo, 2010).
While these explanations might have a certain intuitive appeal, the evidence in support of loneliness leading to poor health behaviors remains equivocal. A review of the research examining the association between loneliness and physical activity found that nearly two-thirds of the studies in this area were cross sectional (Pels & Kleinert, 2016). Evidence from the longitudinal studies showed that while loneliness was associated with decreased physical activity, there was also evidence suggesting that inactivity may lead to feelings of loneliness over time. Findings from intervention studies indicate that physical activity may play a role in alleviating loneliness (Pels & Kleinert, 2016). Similarly, a review of the association between loneliness and smoking found that 13 of 25 studies reported a significant association (Dyal & Valente, 2015), but here, too, most studies were cross-sectional. Thus, it is unclear whether feelings of loneliness lead to individuals taking up smoking or whether smokers are likely to become lonelier over time. There is some support for the latter hypothesis, with social network analysis of the Framingham Offspring Cohort showing that with a growing number of individuals quitting smoking over time, smokers are moved to the periphery of their social networks (Christakis & Fowler, 2008). This may, in turn, lead to feelings of loneliness. There is limited evidence suggesting greater solitary drinking (Arpin, Mohr, & Brannan, 2015) and poorer food choices (Henriksen, Torsheim, & Thuen, 2014) among lonely adults, and increased substance use among lonely when compared with non-lonely adolescents and young adults (J. T. Cacioppo et al., 2002; Stickley, Koyanagi, Koposov, Schwab-Stone, & Ruchkin, 2014). Further work in this area is necessary.
Sleep has important restorative functions. Sleep duration (long or short sleep) have been associated with mortality and a range of chronic health conditions such as diabetes (Cappuccio, D’Elia, Strazzullo, & Miller, 2010a, 2010b). There is growing evidence suggesting that loneliness may affect sleep, with lonely individuals reporting poorer sleep quality, more disturbances, greater fragmentation, and less sleep efficiency when compared with non-lonely individuals (J. T. Cacioppo et al., 2002; Kurina et al., 2011). Daily feelings of loneliness have been found to be associated with feelings of tiredness and low energy on the following day, with evidence also in support of bidirectional associations (Hawkley, Preacher, & Cacioppo, 2010). Evidence in this area is, however, quite limited.
Lonely individuals tend to evaluate events in their lives as more stressful (J. T. Cacioppo et al., 2000). Indeed, the feeling of loneliness itself acts as a stressor (House, 2001). Further, lab-based and naturalistic studies show that lonely and non-lonely individuals differ in their reactions to stress, as evidenced by changes in a range of biological markers including cardiovascular profiles, cortisol profiles and immune function. In a lab-based study, lonely college students had higher total peripheral resistance and lower cardiac output in response to stressful tasks when compared with non-lonely students (J. T. Cacioppo et al., 2002). A similar pattern was observed in a study examining ambulatory blood pressure (Hawkley, Burleson, Berntson, & Cacioppo, 2003). The authors suggest that this pattern may contribute to higher blood pressure over time in lonely individuals (J. T. Cacioppo et al., 2002; Hawkley et al., 2003). Also age-related increases in blood pressure are more marked among lonely individuals (J. T. Cacioppo et al., 2002; Hawkley, Masi, Berry, & Cacioppo, 2006). On the other hand, loneliness associated with a naturalistic stressor (migration) was not found to be associated with heart rate or heart rate variability (Gouin, Zhou, & Fitzpatrick, 2015).
Lonely individuals also show dysregulation of the HPA axis, as marked by changed cortisol profiles. Lonely individuals show a higher cortisol awakening response when compared with non-lonely individuals (Adam, Hawkley, Kudielka, & Cacioppo, 2006; Steptoe, Owen, Kunz-Ebrecht, & Brydon, 2004), but flatter cortisol profiles over the day (Doane & Adam, 2010). However, findings to the contrary have also been reported, with Cole et al. (2007) finding no significant differences in circulating cortisol levels between lonely and non-lonely adults and loneliness not being associated with urinary cortisol in the Chicago Health, Aging, and Social Relations Study (Hawkley et al., 2006). Further, in a lab-based stress task, increasing loneliness was associated with decreased cortisol responsiveness (Hackett, Hamer, Endrighi, Brydon, & Steptoe, 2012).
Genome-wide analysis indicates that genes associated with the anti-inflammatory glucocorticoid receptor pathway were underexpressed, while the proinflammatory NF-kB/Rel transcription pathway was overexpressed among lonely participants when compared with non-lonely participants (Cole et al., 2007). Data from the Taiwanese Social Environment and Biomarkers Study also showed that leukocyte sensitivity to glucocorticoid regulation was lower among participants who reported being lonely than among non-lonely participants (Cole, 2008). These findings may represent pathways through which loneliness leads to inflammatory diseases. In laboratory studies, lonely participants respond to stress tasks with increases in fibrinogen, natural killer cell response, interleukin-6, interleukin-1 receptor antagonist, and chemokine monocyte chemotactic protein-1 (Hackett et al., 2012; Steptoe et al., 2004). However, some studies have reported no significant associations between loneliness and inflammatory markers (Mezuk et al., 2016; Shankar, McMunn, Banks, & Steptoe, 2011).
Cacioppo et al. propose a model of loneliness placing the brain at the center of the experience of social relationships (J. T. Cacioppo, Cacioppo, Capitanio, & Cole, 2015; S. Cacioppo et al., 2014). According to this model, loneliness as an aversive state leads the brain to take steps that help protect the individual in the short term. These changes include a greater vigilance for social threats, poorer sleep, biological changes such as activation of the HPA axis and changes to immune function, decreased impulse control, and increased depression. While some of these changes may be beneficial immediately, over prolonged periods of time these may be detrimental to health. Hence, chronic loneliness may be particularly damaging to health. Much of the work presented in support of this model is based on animal research. Further, the evidence in support of some mechanisms such as HPA axis activation, sleep disruption, and immune function in humans is mixed. However, this model offers a useful framework for future work into understanding the processes through which loneliness affects health.
Recognition of the harms associated with feelings of isolation is growing. Loneliness, particularly among older adults, has been termed as an important public health threat. Further research is required to elucidate some of the mechanisms through which loneliness affects health.
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