Loneliness

Abstract

Loneliness is the distressing experience that arises when a person perceives a deficiency in the quality or quantity of their social relationships; it is a perception, and it is only modestly related to how much social contact a person actually has. MeSH classifies loneliness under social isolation, the objective state with which it is often confused. This article covers its definition and measurement, its distribution by age and country, the social-cognitive account of vigilance for social threat, its health associations and intervention trials. The central dispute is whether loneliness harms health in its own right or mainly marks the objective isolation that travels with it. Three interactive demos show the gap between desired and actual relationships, the reported mortality estimates for loneliness and isolation side by side, and the loneliness regulatory loop.

Keywords: loneliness, perceived social isolation, social cognition, UCLA Loneliness Scale, social threat

Loneliness was a problem of measurement before it was a problem of theory. The authors of the original UCLA Loneliness Scale wrote that research on loneliness had been hindered by the lack of a simple and reliable assessment technique (Russell et al., 1978), and a later survey scale was introduced because most studies of social relationships in later life focused on the amount of social contact, not on individuals' perceptions of social isolation (Hughes et al., 2004). Four decades of research later, a review could describe loneliness as increasingly recognised as the next critical public health issue (Lim et al., 2020). What follows traces how a subjective state became a measurable risk factor, and how far the evidence supports that status.

What Loneliness Is

Loneliness is defined by perception, not by circumstance. Perlman and Peplau's social psychology of loneliness framed it as a discrepancy between the social relations a person desires and those they achieve (Perlman & Peplau, 1981). Individuals experience loneliness when they perceive a deficiency in the quality or quantity of their social relationships (Mund et al., 2020). One review calls it a distressing emotional state that motivates individuals to renew and maintain social contact (Spithoven et al., 2017), and another states plainly that loneliness is not simply being alone (Hawkley & Cacioppo, 2010). The difference is measurable: in two population-based studies, objective and subjective isolation were related, but the relationship was relatively modest, indicating that the quantitative and qualitative aspects of social relationships are distinct (Hughes et al., 2004).

Loneliness also has kinds. Weiss's monograph treated it as the experience of emotional and social isolation (Weiss, 1973), and the distinction survives in measurement: loneliness pertains to the feeling of missing an intimate relationship (emotional loneliness) or missing a wider social network (social loneliness) (De Jong Gierveld & Van Tilburg, 2006). A related state is homesickness. Homesickness is a frequent component of relocation, known to be related to certain adjustment difficulties and health problems as well as clinical disorders, and a systematic review of 55 studies of temporary sojourns from home reports patterns of findings on its prevalence, consequences, predictors and prevention (Stroebe et al., 2015). The same review argues that including stressors in the new place when assessing homesickness limits understanding (Stroebe et al., 2015).

Measuring Loneliness

The UCLA Loneliness Scale was first reported as a short, 20-item general measure with high internal consistency (coefficient alpha = .96) and a test-retest correlation over two months of .73 (Russell et al., 1978). A revised version was designed to counter the possible effects of response bias in the original, and a second study showed that although loneliness is correlated with negative affect, social risk taking and affiliative tendencies, it is nonetheless a distinct psychological experience (Russell et al., 1980). Version 3 was highly reliable, with coefficient alpha ranging from .89 to .94 and test-retest reliability over one year of r = .73, and confirmatory factor analyses supported a global bipolar loneliness factor along with two method factors reflecting the direction of item wording (Russell, 1996).

Large surveys needed shorter instruments. A three-item scale with a simplified set of response categories, developed for a telephone survey, appeared to measure overall loneliness quite well (Hughes et al., 2004). The 6-item De Jong Gierveld Loneliness Scale, a shortened version of the 11-item scale tested on two surveys with N = 9,448, confirmed two latent factors and proved a reliable and valid instrument for overall, emotional and social loneliness that is suitable for large surveys (De Jong Gierveld & Van Tilburg, 2006).

Table 1

Measures of Loneliness, as Described in the Cited Abstracts

Note. Each row lists only what that paper's abstract reports (Russell et al., 1978; Russell et al., 1980; Russell, 1996; Hughes et al., 2004; De Jong Gierveld & Van Tilburg, 2006).

Who Is Lonely

Loneliness is not a disease of old age. In a nationally representative German sample of 16,132 people, the age distribution of loneliness followed a complex nonlinear trajectory, with elevated levels among young adults and among the oldest old; the late-life increase could be explained by lower income, more functional limitations and a higher proportion of single people, while the quantity of social relationships was associated with loneliness regardless of age (Luhmann & Hawkley, 2016). A meta-analysis of 75 longitudinal studies with N = 83,679 found that the rank order of loneliness is as stable as the rank order of personality traits and follows an inverted U-shaped trajectory across the life span, while mean loneliness decreased throughout childhood and remained essentially stable from adolescence to oldest old age (Mund et al., 2020). The meta-analysis concludes that, in contrast to other personality characteristics, changes in loneliness are not generally related to age (Mund et al., 2020), a different picture from the elevated loneliness among the oldest old in the German age comparison (Luhmann & Hawkley, 2016); the first finding comes from longitudinal studies, the second from comparing age groups.

Prevalence differs by place. A systematic review found prevalence data for 113 countries or territories; pooled prevalence for adolescents ranged from 9.2% in South-East Asia to 14.4% in the Eastern Mediterranean region, and for older adults in Europe it ranged from 5.2% in northern to 21.3% in eastern European countries (Surkalim et al., 2022). The same review notes that data for all age groups except adolescents were lacking outside Europe and that evidence on temporal trends of loneliness is insufficient (Surkalim et al., 2022).

The Social-Cognitive Account

One influential theory treats loneliness as an alarm. Perceptions of social isolation increase vigilance for threat and heighten feelings of vulnerability while also raising the desire to reconnect, and implicit hypervigilance for social threat is proposed to alter psychological processes that influence physiological functioning, diminish sleep quality and increase morbidity and mortality (Hawkley & Cacioppo, 2010). The same review uses a loneliness regulatory loop to explain the cognitive, behavioural and physiological consequences of loneliness, and argues that interventions may need to take into account its attentional, confirmatory and memorial biases (Hawkley & Cacioppo, 2010). A developmental review names one component of the evolutionary theory the reaffiliation motive, the motivation to reconnect with others triggered by perceived social isolation; loneliness is often transient because that motive leads to reconnection, but the motive can fail, leading to prolonged loneliness (Qualter et al., 2015).

Figure 1

Two Outcomes of the Reaffiliation Motive

The cognitive evidence is broad. A review interpreting studies through the Social Information Processing model, a framework developed for children's social adjustment (Crick & Dodge, 1994), concluded that lonely individuals have a negative cognitive bias in all stages of social information processing: increased attention for socially threatening stimuli, negative and hostile intent attributions, expectations of rejection, negative evaluations of themselves and others, more prevention-oriented goals and low self-efficacy, a bias that seems specific to the social context (Spithoven et al., 2017). A broader review lists poorer overall cognitive performance, faster cognitive decline, poorer executive functioning, heightened sensitivity to social threats and a confirmatory bias in social cognition that is self-protective and paradoxically self-defeating among the differences associated with perceived social isolation (Cacioppo & Hawkley, 2009); the link to attentional bias and cognitive aging runs through these findings.

Imaging and genetics have followed. In functional imaging, lonely young adults showed weaker ventral striatum activation to pleasant pictures of people than of objects, and greater visual cortex activation to unpleasant pictures of people than of objects, which the authors read as their attention being drawn more to the distress of others (Cacioppo et al., 2009). After 10 hours of total social isolation, participants felt lonely and craved social interaction, and midbrain regions responded selectively to social cues after isolation as they did to food cues after fasting (Tomova et al., 2020). Studies in behavioural genetics indicate that loneliness has a sizable degree of heritability (Goossens et al., 2015), and a genome-wide association study in up to 452,302 UK Biobank participants identified 15 genomic loci for loneliness (Day et al., 2018).

Loneliness and Health

Loneliness predicts depressive symptoms. In two population-based studies of middle-aged to older adults, higher loneliness was associated with more depressive symptoms net of demographic factors, marital status, social support and perceived stress, and latent growth models revealed reciprocal influences over time (Cacioppo et al., 2006). In a later 5-year study of 229 adults aged 50 to 68, cross-lagged analyses indicated that loneliness predicted subsequent changes in depressive symptomatology, but not vice versa (Cacioppo et al., 2010), although the earlier study's growth models revealed reciprocal influences over time between loneliness and depressive symptomatology (Cacioppo et al., 2006).

Associations extend to dementia and the heart. Among 823 older persons free of dementia at enrolment, risk of Alzheimer disease was more than doubled in lonely persons (90th percentile) compared with those who were not lonely (10th percentile), yet loneliness was unrelated to summary measures of Alzheimer pathology at autopsy, so that it was associated with an increased risk of late-life dementia but not with its leading causes (Wilson et al., 2007). Across longitudinal studies in high-income countries, poor social relationships were associated with a 29% increase in risk of incident coronary heart disease and a 32% increase in risk of stroke (Valtorta et al., 2016). In leukocytes from 14 high- versus low-lonely individuals, 209 genes were differentially expressed, with under-expression of anti-inflammatory glucocorticoid response genes and over-expression of pro-inflammatory pathway genes (Cole et al., 2007).

Mortality is where the central dispute lives. A meta-analysis of studies that controlled for several possible confounds found weighted average effects on mortality of odds ratio 1.29 for social isolation, 1.26 for loneliness and 1.32 for living alone, with no differences between objective and subjective isolation (Holt-Lunstad et al., 2015). A meta-analysis of 90 cohort studies including 2,205,199 individuals found both social isolation (pooled effect 1.32) and loneliness (pooled effect 1.14) significantly associated with all-cause mortality (Wang et al., 2023). In 6,500 participants of the English Longitudinal Study of Ageing, however, after adjustment for demographic factors and baseline health, social isolation remained associated with mortality (hazard ratio 1.26 for the top quintile of isolation) but loneliness did not (hazard ratio 0.92), and the authors conclude that efforts to reduce isolation are likely to be more relevant to mortality (Steptoe et al., 2013). The link to social isolation is therefore not a matter of definition only.

Interventions

Qualitative reviews identified four primary intervention strategies: improving social skills, enhancing social support, increasing opportunities for social contact, and addressing maladaptive social cognition (Masi et al., 2011). In that 2011 meta-analysis, single-group pre-post and nonrandomized studies yielded larger mean effect sizes than randomized studies, and among randomized studies the most successful interventions addressed maladaptive social cognition (Masi et al., 2011). A clinical review building on it notes that to date there is no adjunctive pharmacological treatment for loneliness, but that animal research sheds promising light on the issue, and suggests it may soon be possible to combine (social) cognitive behavioural interventions with short-term adjunctive pharmacological treatments (Cacioppo et al., 2015).

A 2021 meta-analysis restricted to randomized trials of psychological interventions included 28 studies with N = 3,039 and found that the interventions significantly reduced loneliness compared with control groups, with a small to medium effect size (g = 0.43); the interventions were of mixed quality, the most common intervention type was cognitive behavioural therapy, and type of intervention was only approaching significance as a moderator (Hickin et al., 2021). The same analysis found considerable heterogeneity in effectiveness, suggesting that future research should explore what works for whom (Hickin et al., 2021).

Worked Example

The mortality estimates can be put on one scale. An odds ratio of 1.26 for loneliness corresponds, in the meta-analysis's own words, to an average 26% increased likelihood of mortality (Holt-Lunstad et al., 2015); the later pooled effect of 1.14 for loneliness, against 1.32 for social isolation (Wang et al., 2023), places the loneliness estimate at a little under half of the isolation estimate's excess (14 against 32 points). In the single adjusted cohort, the hazard ratio for loneliness was 0.92 with a confidence interval of 0.78 to 1.09, which includes 1, while the hazard ratio of 1.26 for the top quintile of isolation had an interval of 1.08 to 1.48, which does not (Steptoe et al., 2013).

The prevalence figures can be compared in the same way. Among older adults in Europe, pooled prevalence was 21.3% in eastern and 5.2% in northern countries (Surkalim et al., 2022), a ratio of about 4.1. The longitudinal meta-analysis pooled 83,679 participants from 75 studies (Mund et al., 2020), about 1,116 per study.

Discussion

Three conclusions follow for cognitive psychology. First, loneliness is a construct about appraisal. Objective and subjective isolation are related only modestly (Hughes et al., 2004), and the cognitive differences associated with loneliness, from threat sensitivity to a self-protective but self-defeating confirmatory bias (Cacioppo & Hawkley, 2009), are differences in how social information is processed (Spithoven et al., 2017).

Second, the health evidence is real but not settled. Loneliness was associated with depressive symptoms over time (Cacioppo et al., 2010), with Alzheimer disease risk but not its pathology (Wilson et al., 2007), and with mortality in meta-analysis (Holt-Lunstad et al., 2015; Wang et al., 2023), yet in a large adjusted cohort the loneliness association with mortality did not survive adjustment for demographic factors and health (Steptoe et al., 2013). Whether loneliness harms health in its own right, or mostly accompanies the isolation and ill health that do, is the question the next generation of studies has to answer.

Third, the intervention evidence has moved from rankings to heterogeneity. The 2011 meta-analysis favoured interventions addressing maladaptive social cognition among randomized studies (Masi et al., 2011); the 2021 meta-analysis of randomized trials found an overall small to medium effect with intervention type only approaching significance as a moderator (Hickin et al., 2021). The cognitive account predicts that changing appraisal should matter most; the 2011 meta-analysis supports that prediction among randomized studies, but in the 2021 meta-analysis intervention type was only approaching significance as a moderator.

Current Directions

Three lines of work are active. Measurement and surveillance: the cross-national review recommends that loneliness be incorporated into general health surveillance with broader geographical and age coverage, using standardised and validated measurement tools (Surkalim et al., 2022). Mechanism: the craving study supports the idea that acute isolation causes social craving, similar to the way fasting causes hunger (Tomova et al., 2020), and the genome-wide study demonstrated a likely causal association between adiposity and increased susceptibility to loneliness and depressive symptoms (Day et al., 2018). Development: the life-span study recommends that future research focus on the specific sources of loneliness in middle-aged adults (Luhmann & Hawkley, 2016), and an update on correlates and risk factors calls for longitudinal, multi-disciplinary and multiple methodologies and for the rigorous evaluation of programs targeting loneliness (Lim et al., 2020).

Common Misconceptions

“Loneliness is the same as being alone.”

Loneliness is not simply being alone (Hawkley & Cacioppo, 2010); in population studies objective and subjective isolation were related, but only relatively modestly (Hughes et al., 2004).

“Loneliness is mainly a problem of old age.”

Loneliness can occur at any life stage: in a large German sample, loneliness levels were elevated among young adults as well as among the oldest old (Luhmann & Hawkley, 2016).

“The harm of loneliness to health is fully established.”

Meta-analyses associate loneliness with mortality (Holt-Lunstad et al., 2015), but in a cohort of 6,500 older adults its association with mortality was not independent of demographic characteristics or health problems (Steptoe et al., 2013).

Glossary

Attentional bias.

In lonely individuals, increased attention for socially threatening stimuli, one stage of their negative social-information-processing bias.

Confirmatory bias.

A self-protective and paradoxically self-defeating bias in social cognition associated with perceived social isolation.

De Jong Gierveld Loneliness Scale.

A measure of overall, emotional and social loneliness, available in an 11-item form and a 6-item form suitable for large surveys.

Emotional loneliness.

The feeling of missing an intimate relationship.

Homesickness.

A frequent component of relocation, related to certain adjustment difficulties and health problems; MeSH lists it as an entry term of loneliness.

Hypervigilance for social threat.

The implicit heightened vigilance that perceived social isolation is proposed to produce, altering psychological and physiological processes.

Loneliness regulatory loop.

A framework used to explain the cognitive, behavioural and physiological consequences of loneliness and to discuss interventions.

Maladaptive social cognition.

The target of one of four primary loneliness-reduction strategies, the one most successful among randomized studies in a 2011 meta-analysis.

Objective social isolation.

The quantitative aspect of social relationships, such as the amount of social contact, distinct from the subjective isolation captured by loneliness.

Perceived social isolation.

A synonym for loneliness used in the research literature.

Reaffiliation motive.

The motivation to reconnect with others that is triggered by perceived social isolation; when it fails, loneliness can become prolonged.

Social craving.

The craving for social interaction reported after acute isolation, with midbrain responses to social cues like those to food cues after fasting.

Social information processing.

A model relating characteristic styles of processing social cues to social adjustment, first applied to children; in lonely individuals a negative bias appears at every stage.

Social loneliness.

The feeling of missing a wider social network.

UCLA Loneliness Scale.

A self-report measure of general loneliness, first reported with 20 items in 1978 and revised in 1980 and in a third version.

Key Researchers

John T. Cacioppo

(1951-2018). Social neuroscientist at the University of Chicago; co-authored the theoretical account of loneliness as perceived social isolation with heightened vigilance for social threat, and longitudinal studies linking loneliness to depressive symptoms. Wikipedia - Google Scholar

Louise C. Hawkley

. Principal Research Scientist at NORC at the University of Chicago; co-authored the review of the consequences and mechanisms of loneliness, the short survey loneliness scale and the life-span study of age differences in loneliness. ORCID - Google Scholar - Faculty Page

Julianne Holt-Lunstad

. Professor of Psychology and Neuroscience at Brigham Young University; led the meta-analytic review of loneliness and social isolation as risk factors for mortality. ORCID - Wikipedia - Google Scholar - Faculty Page

Maike Luhmann

. Professor of Psychological Methods at Ruhr University Bochum; led the study of age differences in loneliness from late adolescence to oldest old age. ORCID - Google Scholar - Faculty Page

Letitia Anne Peplau

. Distinguished Professor of Psychology, emerita, in the Department of Psychology at the University of California, Los Angeles; co-authored the original and revised UCLA Loneliness Scales. Faculty Page

Pamela Qualter

. Professor of Psychology for Education at the Manchester Institute of Education, University of Manchester; led the life-span review of the reaffiliation motive. ORCID

Frequently Asked Questions

What is loneliness in psychology?

Loneliness is what individuals experience when they perceive a deficiency in the quality or quantity of their social relationships (Mund et al., 2020).

Is loneliness the same as social isolation?

No; in two population-based studies objective and subjective isolation were related, but the relationship was relatively modest, indicating that the quantitative and qualitative aspects of social relationships are distinct (Hughes et al., 2004).

How is loneliness measured?

One standard instrument is the UCLA Loneliness Scale, whose third version showed internal consistency from .89 to .94 and one-year test-retest reliability of .73 (Russell, 1996).

Who is most likely to be lonely?

In a German sample of 16,132 people, loneliness was elevated among young adults and among the oldest old, and the late-life increase could be explained by lower income, functional limitations and a higher proportion of single people (Luhmann & Hawkley, 2016).

How does loneliness affect thinking?

A review of information-processing studies found that lonely individuals have a negative cognitive bias in all stages of social information processing, including increased attention for socially threatening stimuli and expectations of rejection (Spithoven et al., 2017).

Is loneliness linked to depression?

In a 5-year study of adults aged 50 to 68, loneliness predicted subsequent changes in depressive symptoms, but not vice versa (Cacioppo et al., 2010).

Does loneliness shorten life?

A meta-analysis reported an average 26% increased likelihood of mortality for loneliness, but a large cohort found that the association was not independent of demographic factors and health problems (Holt-Lunstad et al., 2015; Steptoe et al., 2013).

Can loneliness be treated?

A meta-analysis of 28 randomized trials found that psychological interventions reduced loneliness compared with control groups, with a small to medium effect size of g = 0.43 (Hickin et al., 2021).

References