Abstract
As a social species, humans rely on a safe, secure social surround to survive and thrive. Perceptions of social isolation, or loneliness, increase vigilance for threat and heighten feelings of vulnerability while also raising the desire to reconnect. Implicit hypervigilance for social threat alters psychological processes that influence physiological functioning, diminish sleep quality, and increase morbidity and mortality. The purpose of this paper is to review the features and consequences of loneliness within a comprehensive theoretical framework that informs interventions to reduce loneliness. We review physical and mental health consequences of loneliness, mechanisms for its effects, and effectiveness of extant interventions. Features of a loneliness regulatory loop are employed to explain cognitive, behavioral, and physiological consequences of loneliness and to discuss interventions to reduce loneliness. Loneliness is not simply being alone. Interventions to reduce loneliness and its health consequences may need to take into account its attentional, confirmatory, and memorial biases as well as its social and behavioral effects.
Keywords
Loneliness; Regulatory loop; Physiology; Health behavior; Sleep; Intervention
Introduction
Loneliness is a common experience; as many as 80% of those under 18 years of age and 40% of adults over 65 years of age report being lonely at least sometimes [1–3], with levels of loneliness gradually diminishing through the middle adult years, and then increasing in old age (i.e., ≥70 years) [2]. Loneliness is synonymous with perceived social isolation, not with objective social isolation. People can live relatively solitary lives and not feel lonely, and conversely, they can live an ostensibly rich social life and feel lonely nevertheless. Loneliness is defined as a distressing feeling that accompanies the perception that one’s social needs are not being met by the quantity or especially the quality of one’s social relationships [2, 4–6]. Loneliness is typically measured by asking individuals to respond to items such as those on the frequently used UCLA Loneliness Scale [7]: “I feel isolated,” “There are people I can talk to,” and “I feel part of a group of friends.” The result is a continuum of scores that range from highly socially connected to highly lonely. Each of us is capable of feeling lonely, and loneliness is an equal opportunity tenant for good reason. We have posited that loneliness is the social equivalent of physical pain, hunger, and thirst; the pain of social disconnection and the hunger and thirst for social connection motivate the maintenance and formation of social connections necessary for the survival of our genes [8, 9]. Feelings of loneliness generally succeed in motivating connection or reconnection with others following geographic relocation or bereavement, for instance, thereby diminishing or abolishing feelings of social isolation. For as many as 15– 30% of the general population, however, loneliness is a chronic state [10, 11]. Left untended, loneliness has serious consequences for cognition, emotion, behavior, and health. Here, we review physical and mental health consequences of perceived social isolation and then introduce mechanisms for these outcomes in the context of a model that takes into
consideration the cognitive, emotional, and behavioral characteristics of loneliness.
Loneliness Matters for Physical Health and Mortality
A growing body of longitudinal research indicates that loneliness predicts increased morbidity and mortality [12–19]. The effects of loneliness seem to accrue over time to
accelerate physiological aging [20]. For instance, loneliness has been shown to exhibit a dose–response relationship with cardiovascular health risk in young adulthood [12]. The greater the number of measurement occasions at which participants were lonely (i.e.,childhood, adolescence, and at 26 years of age), the greater their number of cardiovascular health risks (i.e., BMI, systolic blood pressure (SBP), total, and HDL cholesterol levels, glycated hemoglobin concentration, maximum oxygen consumption). Similarly, loneliness was associated with increased systolic blood pressure in a population-based sample of middle-aged adults [21], and a follow-up study of these same individuals showed that a persistent trait-like aspect of loneliness accelerated the rate of blood pressure increase over a 4-year follow-up period [22]. Loneliness accrual effects are also evident in a study of mortality in the Health and Retirement Study; all-cause mortality over a 4-year follow-up was predicted by loneliness, and the effect was greater in chronically than situationally lonely adults [17]. Penninx et al. [15] showed that loneliness predicted all-cause mortality during a 29-month follow-up after controlling for age, sex, chronic diseases, alcohol use, smoking, self-rated health, and functional limitations. Sugisawa et al. [18] also found a significant effect of loneliness on mortality over a 3-year period, and this effect was explained by chronic diseases, functional status, and self-rated health. Among women in the National Health and Nutrition Survey, chronic high frequency loneliness (>3 days/week at each of two measurement occasions about 8 years apart) was prospectively associated with incident coronary heart disease (CHD) over a 19-year follow-up in analyses that adjusted for age, race, socioeconomic status, marital status, and cardiovascular risk factors [19].
Depressive symptoms have been associated with loneliness and with adverse health outcomes, but loneliness continued to predict CHD in these women after also controlling for depressive symptoms. Finally, loneliness has also been shown to increase risk for cardiovascular mortality; individuals who reported often being lonely exhibited significantly greater risk than those who reported never being lonely [14]. In sum, feelings of loneliness mark increased risk for morbidity and mortality, a phenomenon that arguably reflects the social essence of our species.
Loneliness Matters for Mental Health and Cognitive Functioning
The impact of loneliness on cognition was assessed in a recent review of the literature [9]. Perhaps, the most striking finding in this literature is the breadth of emotional and cognitive processes and outcomes that seem susceptible to the influence of loneliness. Loneliness has been associated with personality disorders and psychoses [23–25], suicide [26], impaired cognitive performance and cognitive decline over time [27–29], increased risk of Alzheimer’s Disease [29], diminished executive control [30, 31], and increases in depressive symptoms [32–35]. The causal nature of the association between loneliness and depressive symptoms appears to be reciprocal [32], but more recent analyses of five consecutive annual assessments of loneliness and depressive symptoms have shown that loneliness predicts increases in depressive symptoms over 1-year intervals, but depressive symptoms do not predict increases in loneliness over those same intervals [36]. In addition, experimental evidence, in which feelings of loneliness (and social connectedness) were hypnotically induced, indicates that loneliness not only increases depressive symptoms but also increases perceived stress, fear of negative evaluation, anxiety, and anger, and diminishes optimism and self-esteem [8]. These data suggest that a perceived sense of social connectedness serves
as a scaffold for the self—damage the scaffold and the rest of the self begins to crumble. A particularly devastating consequence of feeling socially isolated is cognitive decline and dementia. Feelings of loneliness at age 79 predicted “lifetime cognitive change” as indicated by lower IQ at age 79 adjusting for IQ at age 11, living arrangements at age 11 and at age 79, sex, marital status, and ideal level of social support [27]. This finding does not rule out a reverse causal direction; cognitive impairments may hamper social interactions, prompt social withdrawal, and thus lead to loneliness. Other studies, however, have indicated that loneliness is a precursor of cognitive decline. For instance, the cognitive functioning of 75–85-year-olds (as assessed by the Mini-Mental State Examination) did not differ as a function of loneliness at baseline but diminished to a greater extent among those high than low in loneliness over a 10-year follow-up [28]. In a prospective study by Wilson et al. [29], loneliness was inversely associated with performance on a battery of cognitive measures in a sample of 823 initially dementia-free older adults. Moreover, loneliness at baseline was
associated with a faster decline in cognitive performance on most of these measures over a 4-year follow-up. This was not true of the converse: cognitive status at baseline did not predict changes in loneliness. In addition, incidence of Alzheimer’s disease (76 individuals) was predicted by degree of baseline loneliness after adjusting for age, sex, and education; those in the top decile of loneliness scores were 2.1 times as likely to develop Alzheimer’s disease than those in the bottom decile of loneliness scores. Depressive symptoms had a modest effect on Alzheimer’s disease risk, but loneliness continued to exert a significant and much larger influence on Alzheimer’s disease than depressive symptoms when depressive symptoms were included in the model [29]. Overall, it appears that something about our sense of connectedness with others penetrates the physical organism and compromises the integrity of physical and mental health and well-being. What that “something” might be is the topic to which we next turn.
Conclusions
Human beings are thoroughly social creatures. Indeed, human survival in difficult physical environments seems to have selected for social group living [95]. Consider that the reproductive success of the human species hinges on offspring surviving to reproductive age. Social connections with a mate, a family, and a tribe foster social affiliative behaviors (e.g., altruism, cooperation) that enhance the likelihood that utterly dependent offspring reach reproductive age, and connections with others at the individual and collective levels improve our chances of survival in difficult or hostile environments. These behaviors coevolved with supporting genetic, neural, and hormonal mechanisms to ensure that humans survived, reproduced, and cared for offspring sufficiently long that they, too, could reproduce [96–98]. Human sociality is prominent even in contemporary individualistic societies. Almost 80% of our waking hours are spent with others, and on average, time spent with friends, relatives, spouse, children, and coworkers is rated more inherently rewarding than time spent alone [99, 100]. Humans are such meaning-making creatures that we perceive social relationships where no objectifiable relationship exists (e.g., between author and reader, between an individual and God) or where no reciprocity is possible (e.g., in parasocial relationships with television characters). Conversely, we perceive social isolation when social opportunities and relationships do exist but we lack the capacity to harness the power of social connectedness in everyday life. Chronic perceived isolation (i.e., loneliness) is characterized by impairments in attention, cognition, affect, and behavior that take a toll
on morbidity and mortality through their impact on genetic, neural, and hormonal mechanisms that evolved as part and parcel of what it means to be human. Future
interventions to alleviate the health burden of loneliness will do well to take into account our evolutionary design as a social species.
Acknowledgments
This research was supported by Grant R01-AG036433-01 and R01-AG034052 from the National Institute on Aging and by the John Templeton Foundation.