Loneliness and Health in Older Adults: A Mini-Review and Synthesis

Abstract

Increasing evidence suggests that perceived social isolation or loneliness is a major risk factor for physical and mental illness in later life. This review assesses the status of research on loneliness and health in older adults. Key concepts and definitions of loneliness are identified, and the prevalence, correlates, and health effects of loneliness in older individuals are reviewed. Theoretical mechanisms that underlie the association between loneliness and health are also described, and illustrative studies examining these mechanisms are summarized. Intervention approaches to reduce loneliness in old age are highlighted, and priority recommendations for future research are presented.

Full text

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Behavioural Science Section / Mini-Review
Gerontology
DOI: 10.1159/000441651
Loneliness and Health in Older Adults:
A Mini-Review and Synthesis
AnthonyD.Ong  a BertN.Uchino  c ElaineWethington  a,b 
Departments of
a  Human Development and
b  Sociology, Cornell University, Ithaca, N.Y. , and
c  Department of
Psychology and Health Psychology Program, University of Utah, Salt Lake City, Utah , USA
and mortality [1–3] . By contrast, loneliness or the per-
ceived absence of positive social relationships has been
linked to diminished longevity
[4] , particularly among
older individuals in whom declining economic resources,
illness, widowhood, and impaired mobility may result in
increased risk for social isolation
[5] .
In this review, we focus on what is known about the
relationship between loneliness and health in later adult-
hood, giving emphasis to the major approaches, empiri-
cal findings, and methodological gaps that currently exist
in the literature. To this end, we review (a) definitions
that distinguish loneliness from related concepts such as
living alone, social isolation, and solitude; (b) estimates of
the prevalence of loneliness in old age; (c) correlates and
health effects of loneliness; (d) potential mechanisms un-
derlying the association between loneliness and health
among vulnerable older individuals, and (e) intervention
strategies to alleviate loneliness in later life. We close with
a discussion of future research directions.
Conceptualization and Measurement of Loneliness
Loneliness is generally understood as the discrepancy
between a person’s preferred and actual level of social
contact
[6] . Researchers have distinguished loneliness
from related concepts such as living alone, solitude, and
social isolation
[2, 5, 7] . At its most basic level, social iso-
Key Words
Loneliness · Social isolation · Older adults · Health ·
Morbidity · Mortality
Abstract
Increasing evidence suggests that perceived social isolation
or loneliness is a major risk factor for physical and mental ill-
ness in later life. This review assesses the status of research
on loneliness and health in older adults. Key concepts and
definitions of loneliness are identified, and the prevalence,
correlates, and health effects of loneliness in older individu-
als are reviewed. Theoretical mechanisms that underlie the
association between loneliness and health are also de-
scribed, and illustrative studies examining these mecha-
nisms are summarized. Intervention approaches to reduce
loneliness in old age are highlighted, and priority recom-
mendations for future research are presented.
© 2015 S. Karger AG, Basel
Extensive research has documented the importance of
social relationships for promoting mental health and pro-
tecting against the development and progression of phys-
ical illness and disease. Integrative reviews of the lit-
erature provide consistent evidence that social relation-
ships – both quantity and quality – are a major
contributing factor in lowering broad-based morbidity
Received: April 1, 2015
Accepted: October 13, 2015
Published online: November 6, 2015
Anthony D. Ong
Department of Human Development
G77 Martha Van Rensselaer Hall, Cornell University
Ithaca, NY 14853-4401 (USA)
E-Mail anthony.ong  @  cornell.edu
© 2015 S. Karger AG, Basel
0304–324X/15/0000–0000$39.50/0
www.karger.com/ger
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lation has been defined as an objective state of having
minimal social contact with other individuals, whereas
loneliness reflects a subjective state of lacking desired af-
fection and closeness to a significant or intimate other
(i.e., emotional loneliness) or to close friends and family
(i.e., relational loneliness). Moreover, although some-
times considered synonymous with living alone , loneli-
ness and living alone are related but not overlapping cat-
egories. For instance, research with older adults demon-
strates that living alone is not necessarily indicative of
loneliness, with many who live alone reporting frequent
social contact and active social involvement in commu-
nity organizations
[8] . Similarly, researchers have distin-
guished loneliness from the experience of being alone or
solitude . The latter reflects a state of social isolation that
involves a voluntary distancing from one’s social net-
work, whereas loneliness is involuntary and more closely
associated with deficits in the perceived quality of one’s
social interactions
[2] . In the remainder of this review, we
focus on work that defines loneliness as the discrepancy
between actual and desired social relationships, a concep-
tualization that is in keeping with historic formulations
of loneliness
[6] and accounts for the role of poor quality
connections.
Individual differences in loneliness are commonly
measured either using single-item, unidimensional scales,
or multidimensional approaches. Single-item questions
of loneliness – such as those found in longer versions of
the Center for Epidemiologic Studies Depression (CES-
D) scale, wherein respondents are asked ‘Do you feel
lonely?’ – are the most common and widely used mea-
sures of loneliness. Although face valid and well-suited
for large-scale, population-based studies, the use of sin-
gle-item direct measures is likely to result in underreport-
ing due to the stigma associated with being identified as
lonely
[9, 10] . Among the most common and widely used
multidimensional scales tapping loneliness are the UCLA
Loneliness Scale
[11] and the de Jong Gierveld (dJG)
Loneliness Scale
[12] . Unlike single-item direct measures
of loneliness, these scales consist of items that exclude any
reference to loneliness.
Items on the UCLA Loneliness Scale assess one’s sub-
jective feelings of loneliness (e.g., ‘How often do you feel
that there are people who really understand you?’, ‘How
often do you feel your relationships with others are not
meaningful?’, and ‘How often do you feel that you are no
longer close to anyone?’). Conceptualized as a unidimen-
sional construct that varies in frequency and intensity
[11] , factor analyses of the 20-item UCLA Loneliness
Scale have revealed anywhere from two to five dimen-
sions, with second-order factor analyses yielding a single
hierarchical loneliness construct. More recently, a short-
ened 3-item version has been developed for use in large-
scale surveys [13] .
Widely used in Europe, the dJG Loneliness Scale
probes both emotional and social dimensions of loneli-
ness with items such as ‘I experience a general sense of
emptiness’, and ‘There are enough people I feel close to’.
Whereas emotional loneliness involves the absence of an
intimate attachment (partner, sibling, close confidant),
social loneliness reflects the absence of a broader com-
munity or social network (friends, coworkers, and neigh-
bors). The social loneliness items found in the dJG scale
(e.g., ‘There is always someone I can talk to about my day-
to-day problems’; ‘There are enough people I feel close
to’) have parallels with items from the UCLA scale (e.g.,
‘I have nobody to talk to’; ‘I am no longer close to any-
one’). Neither scale sets a time frame for responses to
items. Finally, although both the UCLA Loneliness Scale
and the dJG scale conceptualize loneliness as subjective,
they differ in whether they view loneliness primarily as a
global, unidimensional construct (UCLA) or as multifac-
eted phenomenon with separate emotional and social
components (dDG). Overall, the available evidence sup-
ports the need for further measurement research with
older adults that addresses the dimensionality of UCLA
and dJG scales.
Prevalence of Loneliness
The prevalence of loneliness among older individuals
varies across studies as a function of the (a) measure of
loneliness used, (b) populations studied, and (c) age
group and sample sizes considered. For example, using a
single-item direct question from the 2002 Health and Re-
tirement Study (HRS; n = 8,932), Theeke
[14] estimated
that 19.3% of noninstitutionalized or community-dwell-
ing US adults over the age of 65 years reported feeling
lonely for much of the previous week. Similarly, Perissi-
notto et al.
[15] , using the 3-item version of the UCLA
Loneliness Scale in the HRS
[13] , reported that 29% of
respondents aged 75 years or older were lonely, defined
as endorsing one of the loneliness items at least ‘some of
the time.’ Finally, comparative data from a survey con-
ducted by the American Association of Retired Persons
(AARP; n = 3,012) using a national representative sample
estimated that 25% of community-dwelling US respon-
dents over the age of 70 years were lonely
[16] , as mea-
sured by a score of 44 or higher on the 20-item UCLA
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Loneliness Scale. Overall, despite the heterogeneous na-
ture of the measures, sample sizes, and ages considered in
the HRS and AARP surveys, prevalence of loneliness in
US older adults are high enough to warrant concern, with
estimates ranging between 25 and 29% of American
adults aged 70 years and older reporting being lonely.
Similar prevalence estimates have been reported across
European countries. For instance, Yang and Victor
[17]
compared estimates of loneliness in older adults (aged 60
years and older) in 25 European countries (n = 47,099).
Using a single-item measure of loneliness (i.e., ‘How
much of the time during the past week did you feel lone-
ly?’), the authors estimated that the prevalence of chronic
or frequent loneliness was highest in former Soviet states,
including Ukraine (34.0%), Russia (24.4%), Hungary
(21.1%), and Poland (20.1%). Likewise, using data from a
large Norwegian sample (n = 14,743), Nicolaisen and
Thorsen
[18] estimated that 30.2% of Norwegian adults
over the age of 65 years reported being lonely, as mea-
sured by a score of 2 or more (answer categories range
from 1 = not lonely to 6 = intensely lonely) on the 6-item
dJG Loneliness Scale.
Studies conducted in Asia have reported similar prev-
alence estimates of loneliness in relation to age. In China,
for example, a national survey conducted in 2000 (n =
20,255) found that 29.6% of older adults (age 60 years and
older) reported that they ‘often felt lonely’
[19] . Other re-
searchers have reported similar prevalence estimates in
Mediterranean countries. For instance, Stessman et al.
[20] investigated feelings of loneliness among a represen-
tative sample of Israeli residents in Jerusalem aged 70
years and older. Using a single global measure of subjec-
tive loneliness (i.e., ‘How often do you feel lonely?’), the
authors estimated that at the age of 70, 78, and 85 years,
the prevalence of loneliness was 27.9% (n = 95), 23.9%
(n = 124), and 24% (n = 169), respectively.
In sum, the available evidence supports the conclusion
that prevalence estimates of loneliness at older ages are
high enough to justify intervention; however, estimates
vary across studies, reflecting the different measurement
approaches and populations sampled.
Correlates and Health Effects of Loneliness
There is a sizeable literature on the risk factors for
loneliness in older adults. A meta-analytic synthesis of
218 studies by Pinquart and Sörensen
[21] concluded that
loneliness was associated with a constellation of sociode-
mographic, psychosocial, and health-related risk factors
that include being female, widowed, divorced, never mar-
ried; having little contact with significant friends or low-
quality friendship ties; worsening physical health (e.g.,
increased chronic illness and impaired mobility), and
lacking socioeconomic resources (e.g., limited education
and low income). More recent large-scale, population-
based studies of older adults have reported broadly simi-
lar findings
[15, 18] . Moreover, these factors have also
been previously identified as major risk factors for social
isolation among older individuals
[5] .
At older ages, loneliness is also a major risk factor for
broad-based morbidity (both psychological and physi-
cal). As summarized by Cacioppo et al.
[22] , significant
aspects of adult morbidity predicted by loneliness include
depressive symptomatology, physical health, and func-
tional limitations. Indeed, growing evidence indicates
that loneliness is associated with a wide range of health
outcomes in later life, even after adjusting for objective
indices of social isolation. For example, independent of
objective features of social relationships (e.g., living ar-
rangement, number and frequency of contacts, presence
and propinquity of caregivers), loneliness has been asso-
ciated with impaired daytime functioning, reduced phys-
ical activity, lower subjective well-being, and poorer
physical health. Moreover, beyond cross-sectional asso-
ciations, loneliness has been shown to prospectively pre-
dict increased depressive symptomatology, impaired cog-
nitive performance, dementia progression, significant
likelihood of nursing home admission, and multiple dis-
ease outcomes (e.g., hypertension, heart disease, and
stroke in older persons)
[22] .
Higher rates of mortality among lonely older adults
have been reported by a number of researchers
[15, 23,
24] . However, across studies, findings are mixed as to
whether loneliness independently predicts mortality risk
after adjusting for initial health status, health behaviors,
depression, and social isolation. For example, Steptoe et
al.
[25] examined the effects of both social isolation (as-
sessed in terms of contact with family and friends and
participation in organizations) and loneliness (measured
using the short form of the UCLA Loneliness Scale) on
survival in a national sample of 6,500 older men and
women (age 52 years and older) who participated in the
English Longitudinal Study of Ageing (ELSA). Findings
revealed that both isolation and loneliness were associ-
ated with increased mortality; however, following adjust-
ments for demographic, socioeconomic and health fac-
tors, only social isolation continued to significantly pre-
dict survival. By contrast, a recent meta-analytic review of
70 independent prospective studies conducted between
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1980 and 2014 – featuring a total of 3,407,134 partici-
pants – found that after accounting for multiple covari-
ates (e.g., age, gender, socioeconomic status, health sta-
tus, physical activity, smoking), the increased likelihood
of premature mortality was 26% for reported loneliness,
29% for social isolation, and 32% for living alone, respec-
tively
[4] . Of note, the data indicated no difference be-
tween objective and subjective measures of social isola-
tion when predicting elevated risk for early mortality.
However, the authors concluded that given the differenc-
es in measurement approaches in previous research,
questions remain regarding the relative contribution of
loneliness and social isolation to mortality risk and that
more research is needed in this area.
In sum, several forms of social isolation may exist (e.g.,
objective and perceived) that have distinct effects on
health, but, to date, empirical work does not permit draw-
ing strong inferences regarding their relative importance
for adult mortality. In particular, across research studies,
the overall effect size of loneliness on mortality is difficult
to summarize due to the lack of uniform measures of
loneliness
[5] , differences in the inclusion of statistical
controls
[26] , and the use of analytic procedures that ig-
nore survival time and censored data
[24] .
Theoretical Pathways Linking Loneliness to Health
Several theoretical pathways have been proposed to
explain the health effects of loneliness in older adults [for
a review, see
2 ]. As noted, loneliness has been found to be
associated with adverse health behaviors – poorer health
practices (e.g., alcohol use and smoking) and fewer health-
promoting behaviors (e.g., less physical activity, poor nu-
trition) among older persons. Additionally, loneliness is
associated with diminished sleep (e.g., shorter sleep dura-
tion, lower sleep efficiency, greater daytime fatigue) in
later adulthood. Moreover, findings from two longitudi-
nal health surveys of older adults
[27, 28] suggest that
loneliness predicts decrements in subjective sleep quality,
which, in turn, feed forward to further exacerbate subse-
quent loneliness, suggesting a bidirectional causal rela-
tionship.
Alongside the proliferation of research on behavioral
mechanisms has been an increase in studies probing the
neurobiological substrates of loneliness, particularly in
older adults. As reviewed by Cacioppo et al.
[22] , candi-
date neurobiological mechanisms include age-related
changes in neuroendocrine, cardiovascular, and inflam-
matory stress responses; elevated vascular resistance,
blood pressure, and hypothalamic pituitary adrenocorti-
cal activity; leukocyte glucocorticoid resistance reflecting
aberrant ratios of circulating white blood cells, and lower
inflammatory control and diminished immunity.
Cognitive processes have also been implicated as a po-
tential mechanism in the loneliness-health relationship.
For instance, severe and persistent feelings of loneliness
have been shown to impair executive functioning, height-
en sensitivity to negative social stimuli, and erode inter-
personal trust [for a review, see
29 ]. Moreover, recent
work on embodied cognition has suggested that feelings
of loneliness may be instantiated in various mental repre-
sentations including sensorimotor perception, mimicry,
and interpersonal synchrony. Specifically, Cacioppo and
Cacioppo
[30] reviewed data suggesting that experiences
of physical warmth/coldness and feelings of social
warmth/coldness share similar sensorimotor representa-
tions. Moreover, loneliness or perceived social isolation
may play a role in modulating the way in which individu-
als perceive and mirror the expressions and actions of
others, particularly nonverbal cues that may indicate so-
cial rejection.
Finally, a growing body of neuroimaging studies sug-
gests that individual differences in loneliness are reflected
in brain regions associated with basic perception and pro-
cessing of social information
[22] . For example, in line
with behavioral data suggesting that loneliness is associ-
ated with vigilance to social threats and diminished plea-
sure from rewarding social stimuli, a functional magnetic
resonance imaging (fMRI) study found that lonely indi-
viduals showed less activation in the ventral striatum
in response to positive social stimuli compared with
nonlonely individuals
[31] . Furthermore, another study
found that loneliness is linked to reduced gray matter
density in left posterior superior temporal sulcus, a region
known to be involved in early stages of social perception,
including eye gaze processing, hand action, and body
movement coordination
[32] . Notably, the association
between loneliness and posterior superior temporal sul-
cus size was not explained by social network size (a com-
mon component of indices assessing objective social iso-
lation).
In sum, accumulating evidence suggests that adverse
health behaviors, impaired sleep, biological dysregula-
tion, negative social cognition, and regional brain activa-
tion to social in contrast to nonsocial stimuli may be
among the key mechanisms underlying the effects of
loneliness on broad-based morbidity and mortality. Re-
search also suggests that the health effects of each of these
pathways may be most apparent in later life, although
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more research on age differences in the associations be-
tween loneliness and health-related processes is clearly
needed.
Interventions for Loneliness
Turning to intervention studies, a key question is
whether loneliness and social isolation can be alleviated
among older persons. To date, a range of psychosocial
interventions involving diverse study designs have been
developed to reduce loneliness and social isolation in vul-
nerable older adults
[33] . With variable success, these in-
terventions have attempted to improve social skills (e.g.,
through social recreation), enhance social support (e.g.,
via mentoring, home visits), increase opportunities for
social interaction (e.g., telephone outreach, nonverbal
communication), and address maladaptive social cogni-
tion (e.g., psychological reframing or cognitive behavior-
al therapy). Findlay
[34] reviewed 17 relevant interven-
tions that targeted social isolation and/or loneliness in
older individuals and concluded that ‘although numerous
such interventions have been implemented worldwide,
there is very little evidence to show that they work’. The
important methodological issues identified in previous
qualitative reviews of loneliness reduction include differ-
ences in the duration of interventions and frequency of
the interventions sessions, potential for regression to-
ward the mean and selection bias in nonrandomized con-
trolled trials, the need to match interventions to specific
therapies and population characteristics, and the relative
paucity of randomized control trials.
Masi et al.
[33] used meta-analytic techniques to quan-
tify the efficacy of loneliness-reducing interventions. Of
the 50 intervention studies analyzed, 12 were single-
group pre-post studies, 18 were nonrandomized group
comparison studies, and 20 were randomized group com-
parison studies. Within the 20 randomized studies, 10 in-
cluded adults aged 60 years and older, 6 focused on adults
in their middle age, 3 focused on young adults, and 1 in-
cluded children. In addition, 13 of the 20 studies used the
UCLA scale, 2 used the dJG scale, and the remaining 5
studies used other loneliness measures. Meta-analysis of
the randomized studies revealed a small effect size (–0.198,
96% CI = –0.32, –0.08). Compared to other interventions,
those addressing deficits in social cognition had the larg-
est mean effect (–0.598, 96% CI = –0.96, –0.23). Further-
more, follow-up analysis that included potential modera-
tors (gender, age, type of loneliness measure) revealed
that only gender had a moderating influence on the effect
size. Studies with more women in the sample showed a
smaller reduction in loneliness.
In sum, despite important design flaws noted in prior
loneliness reduction interventions, summative findings
from systematic reviews and quantitative meta-analyses
suggest that well-designed loneliness interventions (i.e.,
randomized comparison studies) that target maladaptive
social cognitions (e.g., cognitive behavioral therapy) may
hold promise in mitigating loneliness. This finding is
consistent with the important role that maladaptive social
cognition is believed to play in the initiation and mainte-
nance of loneliness
[29] . Nevertheless, there is a need for
better-designed randomized controlled trials of targeted
interventions designed to alleviate loneliness among vul-
nerable older individuals. Specific groups of older adults
who might benefit from such interventions might include
those suffering from cognitive impairment and dementia,
as well as the ‘oldest-old’ who are at heightened risk for
loneliness due to decreasing opportunities for social con-
nection
[35] .
Future Directions
Existing evidence demonstrates important links be-
tween loneliness and health in older adults. The data re-
viewed indicate that feelings of intense and persistent
loneliness are strongly linked to various forms of psycho-
logical and physical morbidity (e.g., increased depressive
symptomatology, cognitive decline, and chronic illness).
More limited empirical data exists on the impact of lone-
liness on mortality as well as mechanisms through which
successful loneliness interventions enhance health and
well-being in older individuals. Overall, the limitations in
the existing data provide an important impetus for future
work. Below, we highlight several critical but, as yet, un-
resolved issues.
First, as previously noted, it is difficult to summarize
the overall prevalence of loneliness across studies due to
the lack of standardized measures used in previous work.
Thus, a key challenge for future research is to maximize
the comparability of survey questions and instruments
designed to measure loneliness
[5, 26] . The two most fre-
quently used loneliness assessment tools – the UCLA
Loneliness Scale and the dJG Loneliness Scale – have
demonstrated reliability and validity, although as noted,
there is a need for further measurement research that ad-
dresses the multidimensionality of the UCLA and dJG
scales in older adult samples. Data harmonization efforts
aimed to promote common measures of loneliness may
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allow researchers to more easily compare and combine
datasets. By identifying equivalent measures or those with
comparable content, such techniques offer the opportu-
nity for cross-national comparisons of loneliness [36] .
Second, several authors have suggested that there is a
bidirectional relationship between loneliness and various
risk factors (e.g., initial health status, health behaviors,
depression). However, with a few exceptions [e.g.,
24, 23 ],
prospective, longitudinal links between loneliness and
mental and physical health have rarely been examined in
previous mortality studies. In addition to providing a
more rigorous assessment of mechanistic pathways, pro-
spective, multi-wave, longitudinal studies are critically
important in advancing the science of loneliness and
health because they (a) allow for tests of theoretical mod-
els that assume stability of relations over time, (b) help
address questions regarding duration of loneliness and
whether sustained loneliness over time is associated with
health outcomes above and beyond a single report, and
(c) provide evidence against reverse-causality arguments,
which posit that individuals who are ill may also report
more loneliness. Additionally, controlled experimental
studies investigating the effect of loneliness on health out-
comes are especially scarce
[37] . To the extent that expe-
riences of loneliness and social rejection activate the same
basic ‘neural alarm system’
[38] , experimental studies
that employ social rejection paradigms [see also,
39 ] to
induce feelings of social exclusion (vis-à-vis autobio-
graphical recall, film clips, and interactive video games)
may also elicit feelings of loneliness, thereby providing a
conceptual link to previous observational studies of lone-
liness. Additional research in this area is warranted.
Third, an important question for future research is the
extent to which loneliness is confounded with social iso-
lation and other unmeasured third variables. A number
of investigators [e.g.,
7, 20 ] have advocated testing the as-
sociation between loneliness and health through careful
statistical control of potential confounds (e.g., depres-
sion, pre-existing health conditions) as well as closely re-
lated constructs (e.g., objective social isolation). Although
statistical controls are invaluable in nonexperimental re-
search (e.g., prospective epidemiological studies), such
adjustments may obscure the identification of potential
mechanisms of change. For instance, loneliness is linked
to changes in depression over time that may in turn result
in health-relevant biological changes
[40] . Furthermore,
comparative studies in animals may play an especially in-
formative role in advancing understanding of loneliness
and social isolation and their potentially independent un-
derlying mechanisms and treatments. For example, Ca-
cioppo et al.
[39] reviewed evidence suggesting that
among titi monkeys and adult baboons, social isolation
from a preferred companion (i.e., loneliness) is associated
with a range of behavioral and neural effects that are dis-
sociable from isolation per se, including increased vigi-
lance for predatory threats and elevated cardiovascular
activity. Taken together, research that attempts to sub-
stantiate a causal link between loneliness and health out-
comes should consider statistical controls in a theory-
driven manner and the use of animal models to examine
the adaptive significance of loneliness across phylogeny.
Fourth, there is a relative paucity of research examin-
ing the health effects of loneliness in non-Western coun-
tries
[23] . Moreover, little work to date has examined age
differences in the relative potency of theoretical pathways
(e.g., health behaviors, sleep salubrity, biological systems,
social cognition, and regional brain processes) through
which loneliness impacts health. Thus, it remains unclear
which mechanisms might accelerate the rate of morbidity
and mortality in lonely older adults.
Finally, there is a dearth of studies that distinguish old-
er adults who experience transient versus prolonged
loneliness. Whereas transient feelings of loneliness may
motivate individuals to reconnect with other individuals,
prolonged loneliness increases withdrawal and cognitive
vigilance to social threat
[29] . Person-centered approach-
es (e.g., latent growth mixture modeling) that allow for a
mapping of specific subgroups of lonely older adults may
inform targeted intervention programs. Thus, future re-
search should consider interventions that target specific
populations of older adults (e.g., functionally disabled,
hearing impaired, limited mobility) and clarify which in-
terventions are most beneficial for those with varying lev-
els of loneliness.
Conclusion
In this article, we focused on what is currently known
regarding the health effects of loneliness in later adult-
hood, giving emphasis to theoretical predictions, under-
lying mechanisms, and methodological gaps that current-
ly exist in the literature. Although there is growing inter-
est in studying the prevalence and detrimental effects of
loneliness in later life, full understanding of the phenom-
enon is far from complete. Questions remain about
whether the associations between loneliness and health
reflect the effects of loneliness, the effects of objective so-
cial isolation, or the effects of unmeasured variables.
Thus, longitudinal and experimental studies addressing
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the direct, indirect, and moderated effects of social isola-
tion and loneliness on health are urgently needed. More
research is also needed to clarify the brain mechanisms
underlying the association between loneliness and cogni-
tive decline in old age and the extent to which such de-
cline is reversible through intervention. To the extent that
progress can be made on these issues, efforts to combat
loneliness, particularly among older persons, may play an
important role in improving well-being, minimizing
chronic illness, and prolonging life.
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