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Loneliness as an active ingredient in preventing or alleviating youth anxiety and depression: a critical interpretative synthesis incorporating principles from rapid realist reviews


Twenty-seven studies (total participants n = 105,649; range 1–102,072) were included (Fig. 1): 18 from the new searches (Table 1), eight from [17] and one from [11] (Table 2). Twenty-five third sector sources (Table 3) and two M.Sc. dissertations [28, 29] were also included. Please see Supplementary Materials for discussions of the loneliness (Supplementary Tables 3−5), and anxiety and depression measures used in the included studies.

We first outline a conceptual framework of potentially promising approaches for different needs, and the possible mechanisms by which these might work. Iterative development of the framework involved discussions of the review results with academic and lived experience experts and yielded a visual summary of interventions for potential future development and testing, and their content, mechanisms and potential applications (Fig. 2). Within this framework, we then discuss outcomes and study quality for the randomised controlled studies only, as other study designs do not meaningfully pertain to assessing effectiveness. Outcomes for all studies (including effect sizes where available) are summarised in Tables 1 and 2.

We started by categorising the Content as ‘Intrapersonal’, ‘Interpersonal’ and ‘Social’ and then identified the contextual factors that might lend themselves to that particular strategy, and the mechanisms by which the strategy might work, to create three ‘pathways’. ‘Intrapersonal’ level constructs are taken to be those that relate to psychological characteristics and mechanisms and the strategies that specifically target these internal characteristics and mechanisms, including steps that an individual has taken themselves to manage their internal psychological states, such as journaling or exercising to moderate their mood. We use ‘Interpersonal’ to refer to individual-level factors, strategies and mechanisms that require interaction with others: the behavioural manifestations of ‘Intrapersonal’ psychological factors. Although Interpersonal factors are also inherently social, in this framework we use ‘Social’ to refer to strategies that target social interaction per se rather than the underlying psychological (e.g. trust) and behavioural (e.g. social skills) elements involved in a social interaction. ‘Social’ factors and mechanisms of action are taken to be those that relate to the presence or absence of satisfying intimate and community relationships. We acknowledge that there is overlap between these categories: for example, self-confidence and social skills are individual-level variables but we have focused on their behavioural manifestations and therefore describe these as interpersonal-level characteristics. Similarly, although having ASD is an intrapersonal characteristic, the social difficulties that people with ASD encounter are often to a considerable degree the result of negative societal attitudes and expectations that they will impersonate ‘neurotypical’ behaviour. We therefore categorise the communication challenges and difficulties with ‘neurotypical’ social skills encountered by people with ASD as key contextual factors with regard to loneliness, listing them as ‘Interpersonal’ factors, rather than Intrapersonal ones. Moreover, ‘recognising the shared understanding of peers’ is a psychological change in thinking but has been listed under’Social’ mechanisms because it appears to be a key mechanism of change for ‘Social’ strategies that enhance social support or increase opportunities for social contact, and has thus been included in the ‘Social’ pathway. ‘Sense of belonging’ could similarly be listed as an Intrapersonal factor, but has been listed under ‘Social’ because it is the key contextual factor for strategies that increase opportunities for social contact.


‘Context’ captures variation in possible factors underlying an individual’s loneliness. Consequently, ‘Context’ affects which strategy might be feasible, acceptable and effective for particular individuals. Rather than focusing on specific demographic groups, the synthetic constructs within ‘Context’ represent key causes of loneliness that could result from different combinations of predisposing, precipitating and maintaining factors (Fig. 2). For example, a young person may be hospitalised, a refugee, or have recently started university, but all of these experiences could lead to ‘Social Factors: Lack of Close Relationships’. These constructs were drawn out of consultation with the LEAG about possible underlying causes of youth loneliness and formulated with reference to the included published and grey evidence, as well as conceptualisations of loneliness from the broader literature (e.g. the distinction between emotional and social loneliness [32]). A combination of these factors might precipitate or maintain an individual’s loneliness.

‘Intrapersonal Factors’ include whether anxiety and depression are already present, and psychological barriers associated with loneliness, such as cognitive biases [33], low interpersonal trust [34], and low self-esteem [35]. ‘Interpersonal Factors’ primarily relate to specific groups facing challenges with communication skills, such as those with ASD, or who lack social confidence, such as those with social anxiety, but might be more broadly applicable (e.g. [36] found that lonely university students reported they felt they lacked social skills). ‘Social Factors’ relate both to lacking or unsatisfactory close emotional relationships with family and friends (‘emotional’ loneliness) and lacking a wider sense of community belonging (‘social’ loneliness), since loneliness can be experienced in relation to one or both of these [32].

These proximate individual-level factors are seen against the backdrop of wider ‘Socio-economic Factors’. For instance, although Lim et al.’s [37] recent review and proposed model of loneliness across the life-course reported limited evidence for the impact of socioeconomic status, greater loneliness was found to be associated with lower income, lower educational attainment, having more economic problems, living in poor neighbourhoods and being a migrant. Such factors can create both loneliness and barriers to addressing loneliness (see ‘Barriers’). These Socioeconomic Factors may lead to loneliness via Intrapersonal, Interpersonal and Social Factors and we focus on these potentially mediating factors in this review, due to the need to develop individual-level clinical and social intervention strategies. It is beyond the scope of this current review to address potential socio-political strategies to address socioeconomic inequalities and thus loneliness, but such strategies are likely to play a major role in reducing loneliness and preventing and alleviating anxiety and depression in this age group (and beyond), and research in this area is much needed.


The ‘Content’ (sub)constructs outline six key active ingredients of strategies to reduce loneliness in young people (Fig. 2).

Content: co-designed and personalised

The ‘Co-designed and Personalised’ construct highlights both that young people need to be integrally involved in the development and testing of intervention strategies, and that different strategies may work for different individuals, and for the same individual at different times. Co-designed and personalised interventions may be individual or collective, and the key element is that strategies suit each individual and their needs, for example, through a flexible modular approach that might combine individual, dyadic and collective elements. The LEAG highlighted the importance of engaging young people in developing strategies to reduce loneliness and the need to address individual needs and interests. The ability to modify intervention delivery may be a key component of success. For instance, the online platform Entourage uses a participant’s unique strengths profile to personalise therapeutic suggestions for social anxiety, and piloting suggests it has potential for reducing loneliness [38, 39]. Different strategies may be needed for different individuals, and over time for the same individual. For example, the LEAG suggested that therapeutic input to manage psychological barriers may subsequently allow better engagement with community-based social opportunities later on. Equally, enhancing meaningful social support may facilitate effective therapeutic processes [40]. Consequently, effective interventions may require multiple elements, depending on individual ‘Context’.

Content: intrapersonal strategies

In contrast to previous loneliness intervention taxonomies, we do not use the terms ‘changing cognitions’ [22] or ‘addressing maladaptive social cognition’ [21] for psychological interventions, in order to encompass a broader range of Intrapersonal Strategies that also included psychoeducation and mood regulation. Eight quantitative studies used some form of ‘Therapy’ (Tables 1 and 2). Two interventions for social anxiety involved online or smartphone platforms using positive psychology content designed to improve relationship quality and facilitate social goals [39, 41]. Another study looked at cognitive behavioural therapy (CBT) for high school students reporting depressive symptoms and the mediating effect of loneliness [42], and one looked at the effect of reframing in female college students experiencing loneliness and depression [12]. Studies looking at young people not explicitly experiencing mental ill-health used in-person interventions and focused on groups potentially at risk of loneliness, such as gay and bisexual [43] or incarcerated [44] young men, adolescents at risk of substance abuse presenting at primary care clinics [45], or ‘runaway’ adolescent girls [46].

‘Self-help or Personal Strategies’ could include both direct forms, such as therapeutic apps [41] or self-reflection [47], and indirect forms, such as exercise or listening to music [48, 49]. However, the Co-op Foundation [50] reported a mis-match between the self-help approaches most widely tried by young people, and subjective reports of what helps. For example, ‘waiting for the feeling to pass’ was not always helpful, and ‘trying to make new friends’ seemed a less reliable way of addressing loneliness than turning to existing friends and family. Young people reported that social media can exacerbate loneliness, for example because a contact failed to respond or connections felt inauthentic [51]. One intervention involved quitting social media [52].

Content: interpersonal strategies

Following Masi et al.’s [21] taxonomy of loneliness interventions, the key Interpersonal Strategy is ‘Improving social skills’. Two interventions for using this approach were delivered to people with ASD [53, 54]; in one of these, social skills training was part of an intervention specifically for university students [54]. It is worth noting that interventions aimed at improving social skills for individuals with ASD have been criticised for promoting ‘neurotypical’ social skills, and that LEAG members identifying as having ASD preferred the term ‘communication challenges’ and emphasised that people with ASD may have different ways of interacting that are not necessarily problematic. The LEAG suggested that social spaces that allowed individuals with ASD to engage socially without having to ‘camouflage’ by adopting ‘neurotypical’ social skills would be highly beneficial. A third, school-based, social skills training intervention was designed to help adolescents with social anxiety [13].

Content: social strategies

Following Masi et al.’s [21] taxonomy of loneliness interventions, the key Social Strategies are labelled ‘Enhanced Social Support’ and ‘Increasing Opportunities for Social Contact’. Interventions that ‘Enhanced Social Support’ appeared feasible and acceptable. Approaches included an online peer support forum for university students [36], a Moderated Anonymous Online Group (MAOG) for young adults not in employment or education [55], an in-person school-based intervention comparing peer mentorship versus both peer mentors and a staff mental health support team [16], and in-person peer support groups for homeless youth [56]. A one-to-one peer support intervention for refugee adolescents involved both in-person and online communication [57]. In terms of strategies for helping those already experiencing mental ill-health, a case study reported that meaningful close relationships allowed a young woman to engage more fully with therapy for post-traumatic stress disorder [40].

Meaningful shared activities provided ‘Increasing Opportunities for Social Contact’, as illustrated by the impact of music therapy on hospitalised young people:

“…I don’t feel lonely anymore cause I’m surrounded by people who are all talking or sharing one common thought like what beat are we doing or what is going to come next….” ([27]: page 59)

Music therapy not only brought participants together, but also created a new activity to share with family [27]. Equally, engaging with physical education classes and active leisure time was found to be linked with lower perceived social isolation [58], and part of this benefit may come through engagement with others.

Third sector staff and the LEAG emphasised the importance of creating a variety of accessible ‘safe spaces’ meeting different needs and preferences, including the non-neurotypical social and communication preferences of people with ASD [28, 59,60,61]. Online spaces such as Facebook were not always considered ‘safe’ by young people [51], and more moderated and specific online spaces may be required (e.g. [55]). Third sector sources also advocated addressing bullying to reduce youth loneliness [62,63,64].

Mechanisms of action: intrapersonal

‘Changing thinking patterns and behaviour’, for example in relation to negative self-perceptions and withdrawal, may be a key mechanism in addressing chronic loneliness. A group intervention for high-schoolers with depression included a focus on replacing negative cognitions with positive ones, as well as on increasing participant involvement in pleasant activities [42]. Furthermore, the quantitative association found between loneliness and negative attitudes towards aloneness [52] suggests that reframing such thinking might be a potential intervention target. We did not find interventions focusing on changing social cognitions, such as interpreting ambiguous social stimuli as threatening, despite theoretical grounds for expecting such interventions to be promising [33].

Another potential psychological mechanism was ‘Building a positive attitude to oneself’, which was given preliminary support as a plausible mechanism by the qualitative literature and was emphasised by the LEAG. Associated qualitative themes included greater self-awareness [47], self-reliance [48], self-confidence [49], and self-efficacy [56].

Creating a sense of ‘purpose, ownership and control’ might counteract feelings of helplessness about chronic loneliness (LEAG). For example, the CBT-based online Entourage platform uses bespoke therapy comics to help users with social anxiety work towards their goals (e.g. attending a party) using a strength-based approach, alongside support from e-mentors (trained clinicians and peer mentors) who provide opportunities for social connectedness [38, 39].

Mechanisms of action: interpersonal

‘Building social skills’ and ‘building social confidence’ are plausible interpersonal mechanisms for reducing loneliness. For instance, participants in an intervention for ASD university students reported:

“Well I figured out…how to change my social skills and little bits and pieces that I didn’t know were actually very negative.” ([54]: page 25)

“For the first time in my life, my friends from group and I went to [coffee shop]…I’ve had good opportunities from this group to practice good social skills and how to apply them elsewhere.” ([54]: page 25)

A similar increase in social confidence was echoed for an intervention for homeless youth:

“I’m a bit more outgoing and, like, I’ll go do more things now. I’m not so shy. I used to be really shy. (19-year-old)” ([56]: page 70)

Mechanisms of action: social

Having meaningful companionship seems to be a key way to alleviate loneliness [48, 51, 56, 65]. For instance, although social media can be seen as a useful way to maintain contact with family and friends,

[the] sense of connectedness to the world through Facebook dissipates if people cannot establish meaningful communication, beyond greetings. ([51]: page 11)

The importance of ‘consistent social support’ from a relatable adult to build trust was highlighted by third sector staff [28] and in the published literature ([49]: page 182):

“… it was incredibly nice to have an adult I could call when I wanted…”

The Social Mechanisms construct ‘Recognising the shared understanding of peers’ was strongly supported for in-person and online group activities, and relevant to medical students [47], hospitalised youth [27], young people with a parent suffering mental ill-health [49], youth not in education or employment [55], and university students with depression [36] or ASD [54].

“I think it just makes me feel better, just knowing there’s people out there just like me [with ASD]…I know I have people to talk to and people that I can ask for support”. ([54]: page 25)

In evaluating their intervention, [55] noted that their Moderated Anonymous Online Groups (MAOGs) should be specific to both location and the young people’s situation, for example having shared experiences of being bullied. Communicating about shared experiences might overcome the barrier of ‘not talking about loneliness’ identified by third sector staff [28, 29] and reported for homeless youth [65] and students [48]. Finding commonality and belonging with others is likely to help ‘create meaningful relationships’ and ‘build a sense of community’, as well as potentially addressing psychological barriers such as mistrust.

Activities that ‘build social identity’, such as music therapy ([27]: page 94) or activities that facilitate shared family identity [66], could plausibly reduce loneliness through increasing feelings of belonging. For instance, a peer-support group for ASD university students facilitated identity-building:

“Trying to find who I am. Trying to figure out my identity. Even with the ASD, the spectrum disorder, knowing that I can pretty much do anything that anyone else can. I just have a back-up system [the support group].” ([54]: page 25)

A number of third sector and policy sources advocated training of parents, educators, service providers and community members to improve understanding of loneliness and specific needs, for example associated with disability, mental ill-health or particular social and communication needs, as well as anti-bullying campaigns [62–64, 67–70]. The LEAG proposed addressing familial, community and societal stigma related to loneliness and mental ill-health as an important backdrop to individual-level strategies.


Individual hurdles probably mediate whether the strategies outlined above are effective. For example, a mentoring scheme would be inappropriate for someone who is housebound with severe anxiety or depression, but might suit someone with milder symptoms. Individual hurdles to addressing chronic loneliness may include psychological barriers such as not wanting to be a burden and feeling that others do not share the same experiences [48, 49], as well as situational factors such as caring responsibilities or work patterns (LEAG). The LEAG also raised being a refugee as being both a risk factor for loneliness (as also reported by [37]) and a potential barrier to addressing loneliness: for instance, due to language barriers creating challenges to accessing information and engaging with available support and activities, as well as a potential lack of access to employment and the social networks that work can provide, or the financial resources to engage with community activities that provide opportunities for social interaction. Qualitative data suggested that receiving professional therapy might help overcome the barrier of not wanting to be a burden:

“Having somebody external that didn’t know me personally so that I didn’t feel guilty about telling them about what was going on would have really helped me to be able to talk about what I was feeling…” ([48]: page 24)

Broader practical hurdles include the inaccessibility of services and community assets related to transport, finances, disability, neurodiversity, waiting times, and the digital divide, as well as whether an individual’s interests are catered for locally [59,60,61,62,68]. It is likely that digital exclusion has presented a substantial barrier during the current COVID-19 pandemic. Social hurdles include stigma of both loneliness and mental ill-health, which relates to the tendency to not discuss loneliness [28, 65], lack of understanding from service providers [59,60,61], and unsupportive home environments (LEAG, [29]).

Which aspects of interventions may be most effective, and in which combinations?

Through a CIS approach incorporating RRR principles we developed a conceptual framework that can be used to generate testable hypotheses about which strategy(s) might work best for whom and why. The conceptual framework proposes possible pathways through which particular “Context” factors might influence which “Content” is most effective for which group of young people under which circumstances. For instance, it is plausible that if loneliness primarily arises from psychological barriers including anxiety or depression, then therapy may be most effective in reducing loneliness, acting through intrapersonal mechanisms such as changing thinking and behaviour that help build more positive attitudes to self and others and which feed back into reduced anxiety and depression (the ‘Intrapersonal’ pathway). In contrast, if an individual would like support building communication skills or confidence, for example due to ASD, interventions focusing on these needs may be more effective (‘Interpersonal’ pathway). Lacking close relationships might be best addressed through enhancing social support via peer mentors or support groups, whereas a lack of belonging might be alleviated through shared activities such as music-making or sports, all of which can help individuals recognise commonality and build connections with others (‘Social’ pathway).

To complement the CIS-derived framework, in this section we outline the current state of the evidence for the effectiveness of interventions in these ‘Intrapersonal’, ‘Interpersonal’ and ‘Social’ pathways. Convincing assessment of the effectiveness requires fully-powered RCTs. Only nine of the 27 included studies (33%) were randomised controlled trials [12, 13, 16, 42, 44, 45, 52, 53, 55]. Of these, only two report power calculations [16, 44]. First, Rohde et al. ([44]: n = 109] report an effect size calculation, with this pilot study being powered to detect medium to large effect sizes. However, no significant difference between the CBT Coping Course treatment and control groups of incarcerated young men was found for loneliness, and the significantly greater improvements in externalising scores, self-esteem and reduced suicide-proneness in the treatment group compared to controls showed only small effects sizes (Table 2). Second, Larsen et al. [16] indicate in their study protocol [71] that a sample of 975 students and 49 classes was needed to detect a small effect size of 0.25. The retained sample size of 1937 high school students in their study suggests that this trial is potentially adequately powered, but they do not report how many classes participated and in their discussion of study limitations the authors report lack of statistical power due to the low number of participating schools (n = 17 schools), since the analyses were adjusted for the clustered structure of the data. This study found no effect of the school-based intervention on students’ mental health problems or loneliness, and severity actually increased in all conditions [16] (Table 2). However, girls in the multi-tier group, who received professional support with mental health in addition to having peer mentors and class-based activities that aimed to enhance the psychosocial environment of the school, had a significantly smaller increase in mental health problems compared to girls in the control group [16]. Both these studies were quality rated as ‘fair’. In summary, the two RCTs that appear to have been sufficiently powered found no significant effect of either intervention on loneliness, thus yielding no evidence for the effectiveness of ‘Intrapersonal’ (CBT Coping Training) or ‘Social’ (improved social support in schools) strategies.

Of the RCTs that did not explicitly report sufficient power, four primarily involved Intrapersonal Strategies (Tables 1 and 2). First, undergraduate psychology students with moderate depression receiving a “reframing” intervention were found to experience greater reductions in depressive symptoms than those in “self-control” intervention or control conditions, but loneliness was found to decrease over time irrespective of condition [12]. The sample size for this study was n = 57 and it was quality rated as ‘fair’; no effect sizes were reported. Second, it was found that quitting social media sites did not change social or emotional loneliness compared to controls continuing use as usual [52]. However, this study was quality rated as ‘poor’ (n = 77). Moreover, this finding contrasts with an earlier RCT [72], which found that in a sample of undergraduates (n = 143) reduced use, rather than complete cessation, of Facebook, Instagram and Snapchat led to a greater reduction in loneliness and depression than in a ‘behaviour as normal’ control group (please note that this paper was not included in our initial analysis because our quantitative searches aimed to update Loades et al. [14] and did not include papers before 2020—we thank an anonymous reviewer for bringing this paper to our attention). Third, loneliness significantly decreased in adolescents at risk of alcohol and marijuana use presenting at primary care clinics receiving peer network counselling compared to active controls in a study quality rated as ‘good’ and with a sample size over 100 (n = 117), albeit with a minimal effect size [45]. Fourth, CBT yielded greater reductions in loneliness and depressive symptoms in a group of at-risk adolescents with elevated depression symptoms compared to controls with no effect size reported and a small effect size, respectively, in a ‘good’ quality study with a relatively large sample size (n = 341) [42]. While the findings were mixed regarding Intrapersonal Strategies, it is worth noting that both studies with sample sizes over 100, which were both quality rated as ‘good’, found significant decreases in loneliness after peer network counselling or CBT compared to controls, although effect sizes were small or not reported [42, 45].

Two further RCTs examined ‘social skills’ training interventions (Table 2). The first was quality rated as ‘fair’ but the authors explicitly identified lack of statistical power as a limitation of their study, and present their findings as preliminary findings from a pilot study: in a group of adolescents with ASD, they found large effect sizes for reductions in loneliness and improvements in ‘social skills’ after social skills training with or without peer supporters compared to waiting list controls ([53]: n = 34]. In the second study, which was quality rated as ‘good’, a similar sample size was used (n = 35), suggesting that this can also be considered a pilot study: moderate to strong effect sizes were found for greater reductions in social anxiety in participants receiving social skills training compared to waitlist controls, but no difference in loneliness was found between conditions over time [13]. Pilot findings are therefore mixed regarding Interpersonal Strategies, with some suggestion that ‘social skills’ training maybe particularly useful for young people with ASD in addressing their loneliness.

Regarding Social Strategies, in a quasi-experimental study in which young adults not in employment or education were randomly allocated to either join a moderated anonymous online group or not, no significant changes in quality of life or loneliness were detected ([55]: n = 147; quality rated as “fair”) (Table 1). Alongside the apparently well-powered school-based RCT described above [16] (Table 2), which did not find any effect on loneliness or mental health of class-based activities, peer mentors or a professional mental health support team, this yields no evidence so far of the effectiveness of Social Strategies for addressing loneliness in young people.


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