i. Alone in the Crowd: The Structure and Spread of Loneliness in a Large Social Network, by Cacioppo, Fowler, and Christakis.
“The discrepancy between an individual’s loneliness and the number of connections in a social network is well documented, yet little is known about the placement of loneliness within, or the spread of loneliness through, social networks. We use network linkage data from the population-based Framingham Heart Study to trace the topography of loneliness in people’s social networks and the path through which loneliness spreads through these networks. Results indicated that loneliness occurs in clusters, extends up to three degrees of separation, is disproportionately represented at the periphery of social networks, and spreads through a contagious process. The spread of loneliness was found to be stronger than the spread of perceived social connections, stronger for friends than family members, and stronger for women than for men.”
I almost fell down my chair when I read the first half of this sentence: “The average person spends about 80% of waking hours in the company of others, and the time with others is preferred to the time spent alone (Emler, 1994; Kahneman, Krueger, Schkade, Schwarz, & Stone, 2004).” I really shouldn’t have been all that surprised because I’d seen numbers on related stuff before (“the percentage of people living in single person households [in Denmark is] 20,3 %.”) – here’s another link (in Danish), according to which 33% of adult Danes above the age of 25 do not have a cohabitating partner (as can be inferred from the other estimate, only a subset of these people actually live alone. However do note that not all people who do not ‘live alone’ actually interact socially with the people with whom they live; I’m a case in point, as for various reasons it’s exceedingly rare that I socially interact with my roommate). It’s presumably not surprising that someone like me would tend to underestimate how much time most normal people spend in the company of others during an average day, but the magnitude of the difference did catch me by surprise.
“Humans are an irrepressibly meaning-making species, and a large literature has developed showing that perceived social isolation (i.e., loneliness) in normal samples is a more important predictor of a variety of adverse health outcomes than is objective social isolation (e.g., (Cole et al., 2007; Hawkley, Masi, Berry, & Cacioppo, 2006; Penninx et al., 1997; Seeman, 2000; Sugisawa, Liang, & Liu, 1994). […]
Loneliness has […] been associated with the progression of Alzheimer’s Disease (Wilson et al., 2007), obesity (Lauder, Mummery, Jones, & Caperchione, 2006), increased vascular resistance (Cacioppo, Hawkley, Crawford et al., 2002), elevated blood pressure (Cacioppo, Hawkley, Crawford et al., 2002; Hawkley et al., 2006), increased hypothalamic pituitary adrenocortical activity (Adam, Hawkley, Kudielka, & Cacioppo, 2006; Steptoe, Owen, Kunz-Ebrecht, & Brydon, 2004), less salubrious sleep (Cacioppo, Hawkley, Berntson et al., 2002; Pressman et al., 2005), diminished immunity (Kiecolt-Glaser et al., 1984; Pressman et al., 2005), reduction in independent living (Russell, Cutrona, De La Mora, & Wallace, 1997; Tilvis, Pitkala, Jolkkonen, & Strandberg, 2000), alcoholism (Akerlind & Hornquist, 1992), depressive symptomatology (Cacioppo et al., 2006; Heikkinen & Kauppinen, 2004), suicidal ideation and behavior (Rudatsikira, Muula, Siziya, & Twa-Twa, 2007), and mortality in older adults (Penninx et al., 1997; Seeman, 2000).” […]
“Lower levels of loneliness are associated with marriage (Hawkley, Browne, & Cacioppo, 2005; Pinquart & Sorenson, 2003), higher education (Savikko, Routasalo, Tilvis, Strandberg, & Pitkala, 2005), and higher income (Andersson, 1998; Savikko et al., 2005), whereas higher levels of loneliness are associated with living alone (Routasalo, Savikko, Tilvis, Strandberg, & Pitkala, 2006), infrequent contact with friends and family (Bondevik & Skogstad, 1998; Hawkley et al., 2005; Mullins & Dugan, 1990), dissatisfaction with living circumstances (Hector-Taylor & Adams, 1996), physical health symptoms (Hawkley et al., In press), chronic work and/or social stress (Hawkley et al., In press), small social network (Hawkley et al., 2005; Mullins & Dugan, 1990), lack of a spousal confidant (Hawkley et al., In press), marital or family conflict (Jones, 1992; Segrin, 1999), poor quality social relationships (Hawkley et al., In press; Mullins & Dugan, 1990; Routasalo et al., 2006), and divorce and widowhood (Dugan & Kivett, 1994; Dykstra & De Jong Gierveld, 1999; Holmen, Ericsson, Andersson, & Winblad, 1992; Samuelsson, Andersson, & Hagberg, 1998). […] When people feel lonely, they tend to be shyer, more anxious, more hostile, more socially awkward, and lower in self esteem (e.g., (Berscheid & Reis, 1998; Cacioppo et al., 2006)).”
ii. Loneliness matters: a theoretical and empirical review of consequences and mechanisms, by Hawkley & Cacioppo. From the article:
“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 . For instance, loneliness has been shown to exhibit a dose–response relationship with cardiovascular health risk in young adulthood . […] The impact of loneliness on cognition was assessed in a recent review of the literature . 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 , impaired cognitive performance and cognitive decline over time [27–29], increased risk of Alzheimer’s Disease , 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 ” […]
“Our model of loneliness [8, 9] posits that perceived social isolation is tantamount to feeling unsafe, and this sets off implicit hypervigilance for (additional) social threat in the environment. Unconscious surveillance for social threat produces cognitive biases: relative to nonlonely people, lonely individuals see the social world as a more threatening place, expect more negative social interactions, and remember more negative social information. Negative social expectations tend to elicit behaviors from others that confirm the lonely persons’ expectations, thereby setting in motion a self-fulfilling prophecy in which lonely people actively distance themselves from would-be social partners even as they believe that the cause of the social distance is attributable to others and is beyond their own control . This self-reinforcing loneliness loop is accompanied by feelings of hostility, stress, pessimism, anxiety, and low self-esteem  and represents a dispositional tendency that activates neurobiological and behavioral mechanisms that contribute to adverse health outcomes. […]
Loneliness differences in immunoregulation extend beyond inflammation processes. Loneliness has been associated with impaired cellular immunity as reflected in lower natural killer (NK) cell activity and higher antibody titers to the Epstein Barr Virus and human herpes viruses [70, 80–82]. In addition, loneliness among middle-age adults has been associated with a smaller increase in NK cell numbers in response to the acute stress of a Stroop task and a mirror tracing task . In young adults, loneliness was associated with poorer antibody response to a component of the flu vaccine , suggesting that the humoral immune response may also be impaired in lonely individuals.”
iii. One of the studies also cited above: Women, Loneliness, and Incident Coronary Heart Disease, by Thurston & Kubzansky.
To examine associations between loneliness and risk of incident coronary heart disease (CHD) over a 19-year follow-up period in a community sample of men and women. […]
Hypotheses were examined using data from the First National Health and Nutrition Survey and its follow-up studies (n = 3003). Loneliness, assessed by one item from the Center for Epidemiologic Studies of Depression scale, and covariates were derived from baseline interviews. Incident CHD was derived from hospital records/death certificates over 19 years of follow-up. Hypotheses were evaluated, using Cox proportional hazards models. […]
Among women, high loneliness was associated with increased risk of incident CHD (high: hazard ratio = 1.76, 95% Confidence Interval = 1.17-2.63; medium: hazard ratio = 0.98, 95% Confidence Interval = 0.64-1.49; reference: low), controlling for age, race, education, income, marital status, hypertension, diabetes, cholesterol, physical activity, smoking, alcohol use, systolic and diastolic blood pressures, and body mass index. Findings persisted additionally controlling for depressive symptoms. No significant associations were observed among men.”
(The last sentence may be important.)
iv. The clinical significance of loneliness: A literature review, by Heinrich & Gullone. The first parts you can skip without missing out on anything, but there’s a lot of useful stuff in there as well and you shouldn’t give up on it just because the first part isn’t very good (IMO). I’ve quoted extensively from the paper because there’s a lot of stuff in there – from the article:
“With a particular focus on the adolescent developmental period, this review is organized into five sections: Drawing on developmental and evolutionary psychology theories, the nature of social relationships and the function they serve is first discussed. In the second section, loneliness is introduced as an exemplar of social relationship deficits. Here a definition of loneliness is provided, as well as an explanation of why it may pose a situation of concern. This is followed by a review of the prototypic features of loneliness through examination of its affective, cognitive, and behavioral correlates. The fourth section includes a review of theories related to the antecedent and maintenance factors involved in loneliness. Finally, methodological and theoretical considerations are addressed, and conclusions and proposals for future research directions are put forth.” […]
“Empirical evidence […] suggests that lonely and nonlonely people do not differ in either the daily activities they engage in, or in the amount of time they spend alone (e.g., see Hawkley et al., 2003).” [My initial reaction is to be very skeptical about that claim/finding.] “Thus, loneliness is clearly distinguishable from the objective state of solitude, social isolation, or being alone. Indeed, in a study examining adolescents’ perceptions of loneliness and aloneness, Buchholz and Catton (1999) found that loneliness was described as an aversive state arising from a sense of yearning for another person(s), and associated with negative feelings such as sadness and hopelessness. In contrast, however, aloneness was not viewed negatively. […but I’m aware that this distinction is relevant and may be important.] In fact, whereas loneliness is by definition an undesirable condition, aloneness or solitude may actually be a desirable or positive condition fostering creativity, facilitating self-reflection, self-regulation, identity formation, concentration, thinking, and learning (Buchholz & Catton, 1999; Fromm-Reichmann, 1959; Larson, 1999; Larson, Csikszentmihalyi, & Graef, 1982; Storr, 1988; Winnicott, 1958). Burger (1995) and Larson (see Larson, 1999, for a review) have shown that college students and adolescents, respectively, may seek and appreciate solitude for such positive reasons, rather than as a means of avoiding possibly anxiety-provoking social interactions. However, Larson has also shown that while solitude may be associated with cognitive benefits, such as increased concentration, these benefits come at the cost of lowered mood states (e.g., sadness, irritability, loneliness, and boredom).” […]
“loneliness has been found to be significantly associated with shyness, neuroticism, social withdrawal, and a lower frequency of dating, as well as extracurricular and religious participation (Hojat, 1982b; Horowitz, French, & Anderson, 1982; Jones, Freemon, & Goswick, 1981; Russell et al., 1980; Stephan, Faeth, & Lamm, 1988). Associations between loneliness and poorer social interaction quality have also been demonstrated (Hawkley et al., 2003, Jones et al., 1982, Rotenberg, 1994; Segrin, 1998; Wheeler et al., 1983). For example, Hawkley et al. (2003) found loneliness to be related to less positive and more negative feelings during social interactions. More specifically, loneliness was significantly correlated with less intimacy, comfort, and understanding, and more caution, distrust, and conflict. Importantly, Hawkley et al. also demonstrated that these effects of loneliness on social interaction quality were present after controlling for depressed affect and neuroticism.
Perhaps not surprisingly then, loneliness has also been linked to low social competence, peer rejection and victimization, a lack of high quality friendships, and more negative appraisals of social support (Crick & Ladd, 1993; Kochenderfer & Ladd, 1996; Parker & Asher, 1993; Riggio, Watring, & Throckmorton, 1993; Rubin & Mills, 1988). Larson (1999) has also observed that lonely adolescents are rated by parents and teachers as less well-adjusted. Moreover, loneliness has been found to be associated with higher school dropout rates (Asher & Paquette, 2003), poor academic performance (Larson, 1999; Rotenberg, 1999b; Rotenberg & Morrison, 1993), and juvenile delinquency (Brennan, 1982). However, perhaps most pertinent to the issue of psychosocial problems is the consistent finding that loneliness is associated with low self-esteem (Brage, Meredith, & Woodward, 1993; Hymel, Rubin, Rowden, & LeMare, 1990; Jones, 1982; Larson, 1999; Moore & Sermat, 1974; Olmstead, Guy, O’Mally, & Bentler, 1991; Paloutzian & Ellison, 1982; Schultz & Moore, 1988). Yet, despite the typically lower self-esteem of lonely people, Cacioppo et al. (2000) have reported that lonely people have no less social capital to offer than nonlonely people.” […]
“it would appear lonely people experience predominantly negative affect, which can be summarized as four clusters of feelings: desperation, depression, impatient boredom, and self-deprecation. […] while longitudinal investigations (e.g., Brage & Meredith, 1994; Cutrona, 1982; Olmstead et al., 1991) have suggested that low self-esteem plays a causal role in the development and maintenance of loneliness, it is likely that a reciprocal relationship exists between loneliness and low self-esteem (Peplau, Miceli et al., 1982). To elaborate, since social relationships constitute a major aspect of people’s self-conceptions (Parkhurst & Hopmeyer, 1999; Peplau, Miceli et al., 1982; Sippola & Bukowski, 1999), and given its relationship with social relationship deficiencies, loneliness may lead to negative self-conceptions thereby undermining one’s self-regard (Peplau, Miceli et al., 1982), and resulting in a vicious cycle wherein low self-esteem and loneliness reinforce one another.
Not surprisingly then, lonely people have been found to view themselves in a negative and self-depreciating manner, believing that they are inferior, worthless, unattractive, unlovable, and socially incompetent (Horowitz et al., 1982; Jones et al., 1981; Jones & Moore, 1987; Jones, Sansone, & Helm, 1983; Paloutzian & Ellison, 1982; Rubenstein & Shaver, 1982; Spitzberg & Canary, 1985; Zakahi & Duran, 1982, 1985). Lonely people have also been observed to hold greater discrepancies than nonlonely people between their actual selves (i.e., how they believe they are) and their ideal selves (i.e., how they would ideally wish to be; Kupersmidt et al., 1999; Eddy, 1961, cited in Peplau, Miceli et al., 1982).
Unfortunately, given Gardner et al.’s (2000) assertion that “the arousal of social hunger may direct attention toward and bias memory for social cues” (p. 487), and their observation that failure to meet belongingness needs gives rise to selective retention of social information, self-conceptions may also be more salient for lonely people than nonlonely people. In support of this notion, loneliness has indeed been found to be associated with self-consciousness and a heightened degree of self-focus (Goswick & Jones, 1981; Jones, Cavert, Snider, & Bruce, 1985; Jones et al., 1981, 1982; Moore & Schultz, 1983). Moreover,Weiss (1973) has argued that these inclinations may result in a “tendency to misinterpret or exaggerate the hostile or affectionate intent of others” (p. 21). This is a contention that has been at least partially supported by Cutrona’s, (1982) finding that lonely people are more sensitive to rejection.”
Numerous studies have indicated that the social behavior of lonely individuals is marked by inhibited sociability and ineffectiveness. For example, lonely people are typically shy (e.g., Anderson & Harvey, 1988; Cacioppo et al., 2000; Cheek & Busch, 1981; Dill & Anderson, 1999; Hojat, 1982a; Jackson, Soderlind, & Weiss, 2000; Jones et al., 1981; Kalliopuska & Laitinen, 1991; Qualter & Munn, 2002), introverted (Cutrona, 1982; Hojat, 1982a; Jones et al., 1981; Kalliopuska & Laitinen, 1991), less affiliative/sociable (Cacioppo et al., 2000; Cutrona, 1982), and less willing to take social risks (Hojat, 1982a; Jones et al., 1981; Moore & Schultz, 1983). Lonely people also seem to be less assertive than nonlonely people (Bell & Daly, 1985; Cutrona, 1982; Gerson & Perlman, 1979; Hojat, 1982a; Jones et al., 1981; Sermat, 1980; Sloan & Solano, 1984). […] Jones et al. (1982) have revealed that, at least in mixed-sex college student pairs, lonely people make more statements focusing on themselves, respond more slowly to their partner, ask fewer questions, and change the discussion topic more often than nonlonely people. Thus, the self-focused behavior which lonely people appear to engage in during social interactions may undermine relationship development, furthering feelings of loneliness. […]
Rubenstein and Shaver (1980, 1982) have observed that people’s responses to loneliness tend to fall into four categories: active solitude (e.g., study or work, write, listen to music, exercise, walk, work on a hobby, go to a movie, read, play music), spending money (e.g., spend money, go shopping), social contact (e.g., call a friend, visit someone), and sad passivity (e.g., cry, sleep, sit and think, do nothing, overeat, take tranquilizers, watch television, drink or get ‘stoned’). In coping with loneliness, they found that severely lonely people characteristically adopt a ‘sad passivity’ coping strategy, whereas people who are infrequently lonely tend to adopt the other three strategies. […] perceived social skills are affected by loneliness, with greater loneliness being associated with lower self-perceived social competence. Therefore, coping behavior is influenced by perceived social skills, which in turn are negatively affected by loneliness. […] to summarize, lonely people appear to behave in a self-absorbed, socially ineffective manner towards others, and are typically passive when faced with loneliness and stress.”
v. A Meta-Analysis of Interventions to Reduce Loneliness, by Masi, Chen, Hawkley & Cacioppo.
“In summary, meta-analysis of the randomized group comparison studies revealed a small but significant effect of the interventions on loneliness. Of note, interventions that addressed maladaptive social cognition had a sizable mean effect compared to the other intervention types. […] The current study used meta-analytic techniques to determine quantitatively whether the outcomes of loneliness interventions varied based on study design, intervention type, or other study characteristic. Compared to single-group pre-post and nonrandomized group comparison studies, randomized group comparison studies had a small but significant mean effect size (–0.198, p < .05). Within this group, the mean effect size for interventions that addressed maladaptive social cognition was larger than that for interventions that attempted to improve social skills, enhance social support, or increase opportunities for social interaction. A primary criterion for empirically supported therapies is that they demonstrate efficacy in randomized controlled trials (Chambless & Hollon, 1998). By this criterion, our meta-analysis suggests certain interventions, particularly those that use CBT, can reduce loneliness. […]
With an intervention effect size of –0.198, the average treatment group scored 0.198 standard deviations lower in loneliness, which is equivalent to 8.05 × 0.198 = 1.59 units on the UCLA Scale. Thus, with the control group mean at 41.17, the reduction in loneliness in the average treatment group was equivalent to a decrease from 41.17 to 39.58 on the UCLA Loneliness Scale. […] Because clinical significance is defined as “returning to normal functioning” (Jacobson, Roberts, Berns, & McGlinchey, 1999), a 1.59-point decrease in the UCLA Loneliness score clearly did not return study participants to the level of healthy, community-living individuals. Moreover, a meta-analysis of 302 social and behavioral intervention meta-analyses (reviewed in Lipsey & Wilson, 2001) showed that, on average, interventions in this field have generated a mean effect size of 0.50. A mean effect size of –0.198 falls in the bottom 15% of this distribution, suggesting that loneliness interventions to date have not attained the degree of efficacy achieved by interventions targeting other social and behavioral outcomes.”