Social Isolation and Health, with an Emphasis on Underlying Mechanisms

Abstract

Social isolation is a potent but little understood risk factor for morbidity and mortality, and its negative consequences are most profound among the elderly, the poor, and minorities, some of the fastest growing segments of the U.S. population. A steadily increasing number of people are living alone and are therefore more likely to experience social isolation. We discuss four mechanisms--attractiveness, health behavior, stress, and repair and maintenance--by which perceived social isolation might affect health. Our studies show that neither attractiveness nor health behaviors differ as a function of social isolation, but stress and repair and maintenance do seem to be factors. While socially isolated young adults did not report more frequent everyday stressors, they rated everyday events as more intensely stressful. They were also more likely to report passively coping with stressors, and to show greater vascular resistance, a mechanism of blood pressure control previously associated with passive coping and a risk factor for hypertension. Finally, they exhibited less efficacious repair and maintenance of physiological functioning, including slower wound healing and poorer sleep efficiency. These mechanisms have implications for designing appropriate interventions. We advocate a national health care plan that promotes preventive medicine, recognizes the significance of stress-related disorders, and supports the maintenance of social connections across the life span.

Full text

Social Isolation and
Health, with an Emphasis
on Underlying Mechanisms
S39
ABSTRACT Social isolation is a potent but little understood risk factor for mor-
bidity and mortality, and its negative consequences are most profound among the el-
derly, the poor, and minorities, some of the fastest growing segments of the U.S. pop-
ulation.A steadily increasing number of people are living alone and are therefore more
likely to experience social isolation.We discuss four mechanisms—attractiveness, health
behavior, stress, and repair and maintenance—by which perceived social isolation might
affect health. Our studies show that neither attractiveness nor health behaviors differ as
a function of social isolation, but stress and repair and maintenance do seem to be fac-
tors.While socially isolated young adults did not report more frequent everyday stress-
ors, they rated everyday events as more intensely stressful. They were also more likely
to report passively coping with stressors, and to show greater vascular resistance, a
mechanism of blood pressure control previously associated with passive coping and a
risk factor for hypertension. Finally, they exhibited less efficacious repair and mainte-
nance of physiological functioning, including slower wound healing and poorer sleep
efficiency.These mechanisms have implications for designing appropriate interventions.
We advocate a national health care plan that promotes preventive medicine, recognizes
the significance of stress-related disorders, and supports the maintenance of social con-
nections across the life span.
*
Department of Psychology, University of Chicago.
†
Institute for Mind and Biology, University of Chicago.
Correspondence: John T. Cacioppo, Department of Psychology, University of Chicago, 5848 South
University Avenue, Chicago, IL 60637.
Email: cacioppo@uchicago.edu.
This work was supported by the John D. and Catherine T. MacArthur Foundation and by National
Institute on Aging grant PO1 AG18911.
Perspectives in Biology and Medicine, volume 46, number 3 supplement (summer 2003):S39–S52
© 2003 by The Johns Hopkins University Press
John T. Cacioppo* and Louise C. Hawkley
†
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John T. Cacioppo and Louise C. Hawkley
Perspectives in Biology and Medicine
T
HE
21ST CENTURY HAS BEEN HERALDED for revolutions in technology, yet a
quieter but no less dramatic change is occurring in terms of the socio-
demographic structure of the United States.The population of the United States
is now over 273 million—an approximately 7 percent increase from 10 years ago.
In addition, the population is graying. During the 20th century, the rate of
growth in the number of persons 65 and over was approximately four times that
of persons under the age of 65. Currently, more than one out of every six indi-
viduals is age 65 years or older, and the fastest growing segment of the popula-
tion is over 85. The U.S. Census Bureau estimates that, by the year 2050, there
will be more elderly (age 65 and over) than young (14 and under).The costs of
medical care continue to rise more rapidly than inflation or the gross national
product, with a disproportionate amount going to the treatment of aging-related
disorders. According to estimates by Luskin and Newell (1997), by the early
1990s, 36 percent of all hospital stays and 48 percent of total days of doctor care
were for individuals age 65 or over, even though this age group constituted only
about 11 percent of the U.S. population.
The major causes of death in older adults are chronic diseases: myocardial
infarction, stroke, cancer, and diabetes.The risk factors for these diseases—smok-
ing, obesity, high blood pressure, and sedentary lifestyles—are well known, but
one of the strongest and least understood is social isolation (House, Landis, and
Umberson 1988). Changes in marital and childbearing patterns and in the age
structure of U.S. society are projected to produce a steady increase in the num-
ber of older people who lack spouses or children. The average household size
declined from 3.1 in 1970 to approximately 2.6 in 2000, for instance, and house-
holds with only one or two people increased from 46 to 59 percent during the
same time period (Fields and Casper 2001). By 2010, the number of people liv-
ing alone is projected by the U.S. Census Bureau to reach almost 31,000,000—
a 40 percent increase since 1980.The negative health consequences of social iso-
lation are particularly strong among some of the fastest growing segments of the
population: the elderly, the poor, and minorities such as African Americans
(House, Landis, and Umberson 1988).
These facts have stimulated efforts to improve health outcomes by decreasing
social isolation. In a large multi-site intervention study, for instance, patients
received either standard care following myocardial infarction or they received
social support and treatment for depression in addition to standard care. At six
months, patients in the latter intervention reported lower levels of depression
and higher levels of social support than patients in the standard medical care
group, yet, after three years, mortality in the two groups was comparable (24.4
versus 24.2 percent) (ENRICHD 2001; NIH 2001). In a meta-analysis of prior
research on social support and autonomic, neuroendocrine, and immune func-
tioning, the effects of social support were more apparent on basal measures than
on the measures of stress reactivity (Uchino, Cacioppo, and Kiecolt-Glaser
1996). This finding suggests that, in most individuals, the sequence of events
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responsible for the association between social connectedness and health, if causal,
may unfold over years rather than weeks or months. Post-intervention measure-
ment periods of weeks or months allow little time for the filtration of societal,
community, interpersonal, and mental events to manifest in any measurable
pathophysiological or health outcome.
The meta-analysis by Uchino and colleagues (1996) revealed that perceived
social connectedness or support was more strongly associated with lower levels
of autonomic activity (e.g., lower resting blood pressure), better immunosurveil-
lance (e.g., greater natural killer cell lysis), and lower basal levels of stress hor-
mones (e.g., lower levels of urinary catecholamines) than was objective social
connectedness or support. Moreover, cross-sectional research on perceived social
isolation (loneliness) and health outcomes have confirmed an association. For
instance, Herlitz and associates (1998) reported that among 1,290 patients who
underwent coronary artery bypass surgery, ratings of the statement “I feel lonely”
predicted survival at 30 days and five years after surgery, even after controlling
for preoperative factors known to increase mortality (see also Seeman 2000), and
evidence for a possible link between loneliness and cancer was provided by Fox
and colleagues (1994), who found that loneliness measured prior to a mammo-
gram screening was higher among women who later were diagnosed as having
breast cancer relative to women who were proclaimed disease-free.
Underlying Mechanisms
Policy recommendations and interventions to improve social connectedness and
health may benefit from a better understanding of the mechanisms responsible
for the association. Social isolation and connectedness have been defined in var-
ious ways in the literature.We focus here on perceived social isolation, measured
using the UCLA loneliness scale (Russell, Peplau, and Cutrona 1980).
1
In this
paper, we review four major accounts for this relationship: (1) attractiveness;
(2) health behavior; (3) stress; and (4) repair and maintenance. Evidence bearing
on these hypotheses comes from a series of studies we have conducted to explore
how the social world gets under the skin (Cacioppo et al. 2000, 2002a, 2002b;
Hawkley et al., in press). One study involved pretesting over 2,600 undergradu-
ates at a large Midwestern university, followed by more detailed psychological,
behavioral, and physiological assessments of 135 of these students, selected from
the top, middle, and bottom quintiles in terms of their total score on the UCLA
loneliness scale. A second study consisted of a smaller sample of older adults
(median age 65 years) from an apartment building in south Chicago.
1
Perceived social isolation forms the dominant factor underlying the UCLA loneliness scale, a
measurement instrument that, despite its name, does not include the term “loneliness” (Adams et
al. 1988; Russell, Peplau, and Cutrona 1980).
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Attractiveness
According to the attractiveness account, socially active, popular, and con-
nected individuals are also healthier and more physically appealing and intelli-
gent than are individuals who perceive themselves to be relatively socially iso-
lated.This explanation is derived from evolutionary psychology, where Buss and
Schmitt (1993) have argued that physical features (e.g., symmetry, stature, waist-
hip ratio) that are judged to be physically attractive are also features associated
with health and fertility.To assess this hypothesis, physical attractiveness, height,
weight, body mass index, education, age, SAT scores, number of credit hours in
college, grade point average, and number of roommates were contrasted in the
undergraduate students whose total score fell in the lowest, middle, or highest
quintile on the UCLA loneliness scale (Cacioppo et al. 2000). Contrary to this
hypothesis, no significant difference was found on any of these measures.
Individuals from the lowest quintile on the UCLA loneliness scale were found
to score lower on neuroticism and higher on surgency (extraversion), conscien-
tiousness, and social agreeableness than individuals from the highest quintile,
who in turn did not differ on any of these dimensions from individuals from the
middle quintile (Cacioppo et al. 2000). Studies of monozygotic and dizygotic
twins suggest there is a heritable component to feelings of social isolation (Mc-
Guire and Clifford 2000). To the extent that individual differences are con-
tributing to the association between social isolation and health, these data and
previous reports suggest that they are likely to be operating through more com-
plex pathways (Uchino, Cacioppo, and Kiecolt-Glaser 1996). We turn next to
three such mechanisms.
Health Behavior
According to the health behavior account, individuals who are socially en-
gaged and connected, in contrast to those who perceive themselves to be socially
isolated, are exposed to stronger normative pressures from and control by friends
and loved ones to perform healthy behaviors and to access health care when
needed.
2
Having multiple social ties also provides multiple sources of informa-
tion, thereby increasing the likelihood of having access to an appropriate infor-
mation source to foster relevant health behaviors or to minimize stressful or risky
situations (Cohen 2002). If individuals low in perceived social isolation were
characterized by better health behaviors at least in part due to the influence of
friends and loved ones who exerted pressure on them to adopt a healthy lifestyle,
then differences in health behaviors could help account for the association be-
tween social connectedness and health.
2
This account is closely related to the main effects model, which specifies that social connected-
ness is beneficial regardless of life circumstances due, for instance, to the social controls and peer
pressure that influence normative health behaviors (Cohen and Wills 1985).
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Health behaviors have a large and undeniable effect on morbidity and mor-
tality (IOM 2001). However, the epidemiological studies of social isolation and
health that have examined health behaviors have not found them to account for
most of the differences in health outcomes of those low and high in social con-
nectedness (e.g., Seeman 2000). In our survey of over 2,600 young adults and
our more intensive study of 135 of these individuals, we found that individuals
who scored high on the UCLA loneliness scale engaged in comparable weekly
exercise, tobacco use, and caffeine and soda consumption, and slightly less alco-
hol consumption than individuals who scored average or low on this loneliness
scale. Likewise, our study of older adults in Chicago revealed comparable levels
of daily tobacco use, weekly caffeine consumption, weekly alcohol consumption,
medical compliance, use of seat belts, and healthiness of diet across the full range
of the UCLA loneliness scale (Cacioppo et al. 2002a).
Stress
A third perspective, termed the stressful life account, specifies that individuals
who are socially active and connected are also characterized by lower levels of
stress in their lives than are individuals who are lonely and isolated.The stressful
life account does not represent a single homogenous mechanism but instead em-
braces a set of distinct mechanisms that have in common the catabolic actions of
the body for purposes of surveillance, mobilization, and defense (fight or flight).
In one version of this account, perceived social isolation is the long-term con-
sequence of insecure attachment during infancy and anxious or ambivalent
attachment processes as an adult. Secure adult attachments promote trust, stabil-
ity, security, and harmony, whereas insecure adult attachments have the opposite
interpersonal and emotional effects, which in turn produce more frequent acti-
vation of the sympathetic nervous system and of the sympathetic adrenomedul-
lary (SAM) and hypothalamic pituitary adrenocortical (HPA) neuroendocrine
systems. Infant attachment is difficult to assess retrospectively, but poor or inse-
cure attachment as an infant is thought to produce insecure adult attachment
styles (Cassidy 2000). Our investigation of young adults confirmed the hypoth-
esis that adults who felt socially isolated were also more likely to have insecure
(anxious or ambivalent) adult attachment styles (Cacioppo et al. 2000). This
hypothesis has limitations, however, including the malleability of adult attach-
ment styles (e.g., as a function of relationship) and the finding that adult attach-
ment style was unrelated to autonomic and neuroendocrine measures of stress or
stress reactivity.
In a second version of the stressful life account, early or adult attachment
processes are not what is crucial; instead, perceived social isolation (loneliness) is
itself a stressor that produces negative affect (e.g., anxiety, depression), negative
reactivity (e.g., irritability, hostility, mistrust), and lowered feelings of self-worth,
which in turn promote chronic elevations in sympathetic nervous system, SAM,
and HPA activation. Consistent with this reasoning, the motivational potency of
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the absence of personal ties and social acceptance is reminiscent of more basic
drives such as hunger and thirst (e.g., see Baumeister and Leary 1995). Solitary
confinement is one of humankind’s most severe punishments, and ostracism, the
exclusion by general consent from common privileges or social acceptance, is
universal in its aversive and deleterious effects (Felthous 1997; Williams 1997).
Positively, tactile contact is a stronger determinant of mother-infant attachment
than feeding (Harlow 1958). More recently, functional brain imaging studies
have found that cooperation is associated with the activation of the ventrome-
dial orbitofrontal cortex, nucleus accumbens, caudate nucleus, and rostral ante-
rior cingulate cortex (Rilling et al. 2002)—some of the same regions that are
activated by reward (O’Doherty et al. 2001). Evidence from our studies further
indicate that adults who feel socially isolated are also characterized by higher lev-
els of anxiety, negative mood, dejection, hostility, fear of negative evaluation, and
perceived stress, and by lower levels of optimism, happiness, and life satisfaction
(Cacioppo et al. 2000, 2002a).These feelings were not attributable to simple dif-
ferences in the number of stressful life events, as neither the number of major life
events nor the number or negative effect of traumatic life events differed as a
function of perceived social isolation. More importantly, individuals who felt
socially isolated also showed signs of elevated vascular activation and fragmented
sleep, findings to which we will return below.
In the third version of the stressful life account, which has also been termed
the stress-buffering model, having dependable social ties increases the probabil-
ity that an individual exposed to a significant stressor has access to others who
can provide relevant assistance, support, comfort, or relief (Cohen and Wills
1985).Those without such ties do not receive the same levels of tangible, emo-
tional, appraisal, or self-esteem support in times of stress, and, consequently, are
thought to show more frequent activation of the sympathetic nervous system
and the SAM and HPA axes.
Considerable evidence indicates that social connectedness can be especially
helpful during times of significant stress (Cohen 2002; Cohen and Wills 1985),
but our studies, like the prior research, suggest that the detrimental effects of
feeling socially isolated are not attributable solely to weaker buffers in times of
stress. For instance, an experience sampling component of the study, which
involved randomly beeping participants during a normal day to assess what they
were doing and their perceptions and interpretations of their situation, revealed
that individuals in the top, middle, and bottom quintiles on the UCLA loneli-
ness scale were exposed to the same objective stressors and circumstances during
a normal day, but those who felt socially isolated (i.e., those in the top quintile)
perceived the hassles and stresses of everyday life to be more severe and the up-
lifts of everyday life to be less intense than those in the lowest quintile (Hawkley
et al., in press). One possible explanation for this effect is stress buffering by social
ties. Differences in the participants’ ratings of the severity of hassles and stressors
remained, however, irrespective of the presence of others in the situation. In fact,
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social interactions, themselves a potential uplift and a source of pleasure for most
individuals, were not experienced as positively by individuals who perceived
themselves to be socially isolated.
Rather than stress-buffering, therefore, the differences we observed in hassles
and stress may reflect differences in the manner in which people cope with
stressors in their everyday life (Cacioppo et al. 2000). Daily hassles and stressors
include events such as traffic congestion, difficult work assignments, deadlines,
uncooperative equipment or technology, interpersonal conflicts, and perceived
insults or injustices. Stress can contribute to disease by obscuring symptom pro-
files and increasing the delay in seeking care; decreasing medical compliance and
health care utilization; increasing tobacco use and risky behaviors; and diminish-
ing healthy behaviors such as eating well, exercising, and sleeping adequately
(Institute of Medicine 2001). Moreover, although stressors can activate auto-
nomic and neuroendocrine responses to mobilize metabolic resources in support
of the requirements of fight or flight, the stressors of contemporary society typ-
ically do not require or even allow behavioral fight or flight. Consequently, the
autonomic and neuroendocrine reactions shown in response to acute psycho-
logical stressors substantially exceed metabolic requirements (Cacioppo 1994;
Turner 1989).Thus, although somatic activation in response to stressors is ben-
eficial up to a point, excessive autonomic and neuroendocrine activation can
diminish health across time.
Perhaps understandably, the view that stress is uniformly unhealthy has some-
times overshadowed possible individual differences in the appraisal of and cop-
ing with stress. Stress responses evolved because they can foster adaptive actions
and adjustments. Overcoming stressful life circumstances may lead to an increase
in one’s sense of personal mastery or efficacy, help individuals minimize the neg-
ative outcomes of future stress, and increase resilience. The University of Chi-
cago Student Prospectus entitled “The Life of the Mind,” for instance, carries on
its front cover the following statement:
WARNING: Study in this university is known to cause thinking, occasionally
deep thinking.Typical side effects include mild temporary anxiety followed by
profound long-term satisfaction.
This statement is a reminder that growth (muscular, cognitive, personal, social,
and moral) is achieved by confronting and overcoming stressors, and then by
consolidating what could be learned from the experience and recovering from
these stressors. Thus, new challenges and demands can be a source of growth as
well as a source of stress. Differences in appraisals of and coping with stressors
may contribute to and result from successful adaptations to stressors.
Therefore, we assessed the coping mechanisms deployed in response to stress-
ors by individuals who were high, average, or low in perceived social isolation.
Four significant differences were found: individuals low in perceived isolation
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(i.e., high in social connectedness) were more likely to actively cope (e.g., prob-
lem solve), and to seek instrumental and emotional support from others, whereas
individuals high in perceived social isolation were more likely to behaviorally
disengage or withdraw from the stressor (Cacioppo et al. 2002a). Passively cop-
ing or withdrawing from stressful tasks, interactions, or circumstances is reason-
able in certain instances—for example, when one has no control or low efficacy
to learn or cope—but when applied broadly to quotidian stressors, it at best can
retard learning and personal growth and, at worst, can lead to an accumulation
of tasks and stressors that become increasingly burdensome and self-defeating to
address. Individuals who perceive themselves to be socially connected, on the
other hand, not only are more likely to actively cope with everyday stressors, but
are more likely to seek the support and assistance of others to do so. Having
social ties is more like physical fitness than a bank balance: rather than drawing
down on the balance available, using social ties is associated with strengthened
connections, perhaps in part through increased accessibility and in part through
the development of reciprocal obligations and trust.
Interestingly, active coping on laboratory tasks has also been associated with
blood pressure responses governed primarily by increases in cardiac output (a
“cardiodynamic” response served largely by beta-adrenergic and vagal mecha-
nisms), whereas passive coping on laboratory tasks has been associated with
blood pressure responses characterized primarily by increases in total peripheral
resistance (a “hemodynamic” response served largely by alpha-adrenergic and
local vascular mechanisms) (Sherwood, Dolan, and Light 1990). Although our
sample of young adults was normotensive, the underlying physiology matched
this autonomic patterning: individuals who perceived themselves to be socially
isolated were characterized by higher total peripheral resistance and lower car-
diac output than individuals who perceived themselves to be socially connected.
This difference was as apparent at rest (baseline) as during the performance of
orthostatic or psychological stressors, and ambulatory recordings further revealed
that this difference was evident not only in the laboratory but also during a typ-
ical day in their lives (Cacioppo et al. 2002a; Hawkley et al., in press).
Chronic elevations in total peripheral resistance not only means that the heart
muscle must work harder to distribute the same amount of blood through the
circulatory system, but the reduced diameter of the blood vessels may also
increase turbulence in and potential damage to the vasculature. Further, both
central (e.g., baroreceptor reflex) and peripheral (e.g., vascular elasticity) mech-
anisms may degrade over time, diminishing the ability to maintain normotensive
pressure during rest and normal states. Consistently elevated levels of vascular
resistance, coupled with age-related decreases in vascular compliance, may set the
stage for the development of hypertension—a risk factor for a variety of adverse
health outcomes. Indeed, our meta-analysis of the prior literature pointed to ele-
vations in resting blood pressure in older adults as one of the most robust effects
associated with low levels of social support (Uchino, Cacioppo, and Kiecolt-
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Glaser 1996), and we hypothesized the same effect would be found among older
adults who perceived themselves to be socially isolated. Our study of older adults
in Chicago confirmed this hypothesis. Because the sample size was relatively
small, we divided the participants into two groups, low or high perceived social
isolation, based on their scores on the UCLA loneliness scale. Age was positively
and significantly correlated with systolic blood pressure among individuals who
were high in perceived social isolation, whereas individuals who were low in
perceived social isolation (i.e., high in perceived social connectedness) showed
no such age-related increases.
Repair and Maintenance
The final mechanism we have investigated, termed the repair and mainte-
nance account, builds on points raised in the last section—namely, that social iso-
lation may weaken ongoing anabolic processes that serve to repair and maintain
physiological functioning, foster recovery from stress, and contribute to the
expansion of physiological capital and capacities as a function of adaptive trans-
actions with the environment (Cacioppo et al. 2002b; Hawkley and Cacioppo
2003). Marucha, Kiecolt-Glaser, and Favagehi (1998), for instance, studied the
effects of stress on an explicit repair process—wound healing.Two punch biopsy
wounds were placed on the hard palate of 11 dental students, with the first
placed during summer vacation and the second placed on the contralateral side
three days prior to their first major examination of the term. In all 11 partici-
pants, wounds took longer to heal during high-stress than low-stress periods. Six
months after the completion of this study, we located eight of these individuals
and administered the UCLA loneliness scale. Although preliminary, our results
indicated that perceived social isolation was significantly correlated both with
wound-healing time during the summer and with the additional time needed to
wound heal during periods of stress—that is, perceived social isolation dimin-
ished the efficacy of repair mechanisms.
To examine whether perceived social isolation also modulates the potency of
restorative processes, we examined a quintessential restorative behavior—sleep
(Cacioppo et al. 2002b). Sleep deprivation has dramatic effects on metabolic,
neural, and hormonal regulation—effects that mimic those of aging (Spiegel,
Leproult, and Van Cauter 1999).The young adults in our study who had scored
in the top, middle, or bottom quintile on the UCLA loneliness scale spent one
night in the Clinical Research Center of the university hospital. In a double-
blind procedure, a device called the Nightcap (REMview sleep monitor, Res-
pironics Inc.) was used to record sleep during their night in the hospital and dur-
ing several subsequent nights in their residences. Results from both sites revealed
that sleep efficiency was lower and wake time after sleep onset was higher for
individuals from the top than the bottom quintile on the UCLA loneliness scale
(Cacioppo et al. 2002b). Importantly, the Nightcap recordings revealed that total
time asleep did not differ across the groups.The restorative act of sleep simply
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appeared more efficient and effective—that is, salubrious—in individuals who
perceived themselves to be socially connected.
Further evidence for this difference was found using the Pittsburgh Sleep
Quality Inventory (PSQI), a self-report measure of sleep quality (Buysse et al.
1989). Results from the PSQI revealed that the young adults who perceived
themselves to be socially isolated also reported poorer sleep quality, longer sleep
latency, longer perceived sleep duration, and greater daytime dysfunction due to
sleepiness than did individuals who were relatively socially connected—effects
that were replicated in our study of older adults in Chicago, as well (Cacioppo
et al. 2002a). Together, these results provide preliminary support for the notion
that reparative and maintenance processes can serve to detoxify potentially
harmful catabolic processes, thereby fostering growth and expansion of individ-
ual resources that would otherwise be exhausted. The increased effectiveness of
restorative and maintenance processes in socially connected individuals suggests
that these individuals may benefit from an enlarged repertoire of behavioral op-
tions, cognitive and emotional reactions, and physiological responses when con-
fronted by everyday challenges. Expansion of individual resources has interper-
sonal implications that further increase the capacity for growth. For example,
socially connected individuals are more likely to know where to look and whom
to ask for assistance during stressful occasions, thereby increasing the likelihood
of obtaining access to the stress-buffering effects of social support or of remain-
ing focused on the challenge of the task at hand. In a sense, adults may not be
that different from infants who are eager to play, explore, and learn from both
successful and failed attempts when their caregiver is nearby, but are more anx-
ious, inhibited, and sensitive to failure when their caregiver is not.
Conclusions
Most interventions designed to improve social contact have produced somewhat
disappointing results in light of the strength of the risk factor for social isolation.
The empirical association between social isolation and health, however, is mute
regarding the specific behavioral, psychological, and physiological pathways that
may be underlying this association. Specifying these mechanisms, in turn, pro-
vides a roadmap for those interested in interventions and public policy.
We focused here on perceived social isolation, as measured by the UCLA
loneliness scale, rather than social isolation per se. Although there is an associa-
tion between these constructs, the correlation is imperfect. We nevertheless
focused on perceived social isolation because: (1) prior research has also found an
association between this and health outcomes; (2) we reasoned that the pathways
through which social isolation gets under the skin to produce broad-based mor-
bidity and mortality goes through an individual’s social psychology, brain, and
physiology; and (3) delineating the mechanisms linking proximal levels of organ-
ization (social psychological, behavioral, pre-disease physiological pathways) is
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more tractable than delineating these mechanisms using less fine-grain data from
distal levels of organization (e.g., sociological, morbidity, and mortality).
Based on the foregoing, the conclusion to be drawn is not that interventions
cannot work, but that mechanisms responsible for the association between social
connectedness and health should be understood in order to design appropriate
interventions. Candidate mediators at the social psychological level include not
only subjective construals of the social context (e.g., perceived isolation or sup-
port), but also behavioral choices (e.g., exercising, smoking), affective states (e.g.,
hopelessness, perceived stress), and personality traits (e.g., extraversion, neuroti-
cism). Downstream from these psychological processes are candidate physiolog-
ical mediators that entail the engagement of one or more physiological system
(e.g., sympathetic nervous system, HPA axis, immune system), the operation of
basic regulatory functions (e.g., homeostatic maintenance), the activation of
adaptive responses to acute and chronic stressors, the recruitment of catabolic
processes that “cost” the organism, and the engagement of anabolic processes that
maintain and repair the organism.
Although the level of specificity of the mechanisms discussed in this paper is
limited, candidates for attention and further delineation are beginning to
emerge. Several specific variations of the stressful life account, as well as the com-
plementary repair and maintenance account, warrant additional research,
whereas the attractiveness and health behavior accounts of the effects of social
isolation on health received less support. Investigations and public policy, there-
fore, should not be focused exclusively on health behaviors or intractable indi-
vidual differences, but should also consider how economic and public policies
could foster productive coping and restorative physiological processes.
Perhaps unsurprisingly, given the broad-based nature of the morbidity and
mortality associated with social isolation, the various stress and repair mecha-
nisms we found to differentiate individuals from the top, middle, and bottom
quintiles in terms of perceived social isolation were themselves statistically sepa-
rable.The take-home message is clear, though: the social world does not get un-
der the skin through any one means but through a variety of general means
which, combined with physiological or behavioral vulnerabilities, manifest as a
wide array of disorders across individuals.
Given the deleterious effects of perceived social isolation on health and well-
being, one can ask why such feelings evolved in the first place.The reproductive
value of such unpleasant feelings is readily apparent.The need to belong and the
distress of social isolation in offspring fosters maturation and acculturation, as the
offspring are more likely to remain with family and close kin during maturation.
The same motives and affective states help sustain maternal nurturance during
this period. In addition, our relatively recent ancestral heritage as hunter-gather-
ers, coupled with the likely prevalence of malnutrition, would have promoted
forces of selection that opposed social isolation (Fogel 2003).The hunter-gath-
erer who felt no distress when socially isolated would have felt less need to share
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food, but this would also have diminished the likelihood of his/her progeny sur-
viving. That is, hunter-gatherers who had a genetic predisposition to need to
belong and to suffer distress from social isolation may have been more likely to
return to share their food with their family and allies than those without such a
predisposition. Although the latter individuals may well have roamed the earth
better nourished than those who were distressed by social isolation and shared
their food, the abandoned offspring—and the genetic predisposition to thrive in
social isolation—would have been less likely to survive. Perhaps it should not be
so surprising, therefore, that feelings of social isolation in most individuals are
punishing and have an influence on our brain and physiological functioning as
well as on our long-term health.
The policy implications of this work are far reaching. Consider the social cost
of the phenomenal economic growth of the past century. Moving up the socio-
economic ladder has often meant geographical relocation. For decades the eco-
nomic engine has been fueled by social mobility, as it was less expensive to move
specialized labor (executive or technical expertise) to various geographical sites
as needed than to develop the expertise from the extant labor force in each com-
munity.With the organization of labor unions and the rising costs of labor, it be-
came economical to close entire plants and reopen them in communities where
labor was cheaper. Such closings have often had destabilizing effects on small,
closely knit communities. Over the past century, the economic notion of mov-
ing to opportunity has contributed to the reduction in the number of extended
families that live in the same neighborhood.
The same economic engine that has benefited from social mobility should
consider bearing some of the health care costs created by the resulting isolation.
Precedence for this arises from, for example, the government’s conclusion that the
mining industry should bear the environmental costs of restoring the land it strip-
mined. The most recent U.S. Census Bureau statistics continue to show an
increase in the number of people living alone or who have relocated in the past
several years. Contributing to the increase in the number of people living alone
are alterations in the family structure and the aging of America. Social isolation,
which is heightened by living alone and recent relocations, is a major risk factor
for broad-based morbidity and mortality, even after statistically controlling for
known biological risk factors, social status, and baseline measures of health.
Moreover, the negative health consequences of social isolation are particularly
strong among those most in need of societal support: those over 65 years of age,
the poor, and minorities. Given the projections of health care costs and the loom-
ing budget deficits, there is a critical need not only for theory and research to
determine the mechanisms by which social isolation gets under the skin to affect
morbidity and mortality, but for a national health care plan that both supports pal-
liative care and promotes preventive medicine, health behavior, and healthy
lifestyles to address the rising incidence of chronic disease; that recognizes and
deals with stress-related physical and psychological disorders as a means of
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increasing physiological resilience; and that recognizes the importance of con-
necting lives and family—for instance, not by transferring the elderly to cost-
effective care facilities but by capitalizing on their wisdom and their need to con-
nect with, assist, and mentor others in thriving multigenerational communities.
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