An Updated Systematic Literature Review of the Economic Costs of Loneliness and Social Isolation and the Cost Effectiveness of Interventions

Abstract

Purpose

There has been growing interest in understanding the economic impacts of loneliness and social isolation. This study updates a previous review on the economic costs of loneliness and social isolation and the cost effectiveness of related interventions.

Methods

We conducted a systematic search in the MEDLINE, PsycInfo, CINAHL, and Embase databases from 2018 to 13 August 2024, supplemented by a search of the grey literature. Studies included cost-of-illness studies, economic evaluations, and social return on investment (SROI) analyses published in the English language. All studies were evaluated for quality and summarised using a narrative approach. Costs reported were converted into US$, year 2024 values.

Results

In total, 15 studies were included: six cost-of-illness studies, four economic evaluations, and five SROI studies. Cost-of-illness studies primarily examined healthcare and productivity costs. All but one study reported excess costs linked to loneliness and social isolation, ranging from US$2 billion to US$25.2 billion per annum. Among four economic evaluations, three were model-based cost-utility or cost-effectiveness analyses (targeting older adults and the general population), and one was trial based (focusing on low-income individuals with health issues). One study found an intervention cost effective, whereas cost-effectiveness probabilities in others ranged from 54% to 68%. One study concluded that an intervention to reduce severe loneliness in older adults was cost effective but unlikely to be cost saving. All SROI studies reported positive returns, with SROI ratios ranging from US$2.28 to US$13.72.

Conclusion

This review highlights additional evidence on the economic burden of loneliness and social isolation. Future research should explore broader cost impacts beyond healthcare and expand cost-effectiveness studies to younger populations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40273-025-01516-w.

Plain Language Summary

Loneliness is the feeling of being disconnected from others and wanting better social relationships. Social isolation means having few social contacts or relationships. Both are known to affect people’s health and wellbeing, but we do not yet fully understand how much they cost society or whether programmes that aim to reduce them are good value for money. This study updated a previous review done in 2020. We searched four major databases and other sources for studies published in the English language between 2018 and 2024. In total, 15 studies were included: six looked at the overall cost of loneliness and social isolation (called cost-of-illness studies), four assessed the value for money of specific programmes (economic evaluations), and five examined the social and economic benefits of programmes (called ‘social return on investment’ studies). Cost-of-illness studies found that loneliness and social isolation led to extra costs, mostly related to healthcare and lost work productivity, ranging from US$2 billion to US$25.2 billion per year. Of the four economic evaluations, one programme was cost effective, and others had a 54–68% chance of being worth the money. One programme for very lonely older adults was cost effective but unlikely to save money overall. All five studies of the social return on investment showed positive returns, with benefits ranging from US$2.28 to US$13.72 for every $1 spent. This review shows that loneliness and social isolation can be costly. Future research should include costs beyond healthcare and evaluate the cost effectiveness of programmes for a wider range of people, including younger people.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40273-025-01516-w.

Key Points for Decision Makers

Policymakers should recognise loneliness and social isolation as public health issues with substantial economic implications. Estimated yearly costs range from US$2 billion to US$25.2 billion, primarily due to healthcare use and productivity losses.

Although most social return on investment (SROI) studies show favourable outcomes, with returns ranging from US$2.28 to US$13.72 per dollar spent, they are subject to limitations, particularly in establishing a clear attribution of outcomes to the intervention itself. Evidence from full economic evaluations demonstrated that, although not all interventions are cost saving, several are cost effective, justifying further investment.

Existing research largely targets older adults; future work should broaden to other groups and include costs beyond healthcare to fully capture the value of interventions.

Introduction

Loneliness has been defined as a subjective unpleasant or distressing feeling of a lack of connection to other people, along with a desire for more, or more satisfying, social relationships [1]. Loneliness has been linked to health-related mortality and morbidity impacts, especially in terms of adverse mental health outcomes such as depression and non-communicable diseases (including cardiovascular diseases, stroke, and dementia) [2–5]. Loneliness is different from social isolation, which refers to having objectively few social relationships, social roles, group memberships, and infrequent social interaction [1]. Therefore, a person can be socially isolated but not feel lonely if they are satisfied with the amount and nature of their social interactions. Conversely, someone may be surrounded by others and still experience loneliness if their relationships lack emotional closeness or meaningful connection.

The literature on health outcomes related to loneliness and social isolation has grown in recent years, but our understanding of the economic outcomes associated with loneliness and social isolation remains limited. A review published in 2020 by Mihalopoulos et al. [6] identified only 12 studies, of which four estimated the costs of loneliness or social isolation and the remainder examined the cost effectiveness of interventions targeting loneliness and social isolation. Although the review found that most existing studies reported excess healthcare costs associated with loneliness, the reported cost estimates are probably underestimated, as they do not account for costs outside the healthcare sector, such as workplace productivity losses. The economic evaluation studies included in the review demonstrated good value-for-money credentials, indicating that they achieved improved outcomes at a reasonable or lower cost, within commonly accepted willingness-to-pay thresholds. However, limitations included the differences in methods and contexts, which prevented comparability, and the lack of studies conducted alongside high-quality study designs. Most studies adopted a social return on investment (SROI) methodology, where the translation of outcomes into monetary terms often involves subjective judgement. A general issue identified by the review was the predominant focus on older adults, highlighting the urgent need for further research among children, adolescents, and working-age adults.

Although interest in loneliness research was increasing before the COVID-19 pandemic, the pandemic itself marked a significant turning point, as it compelled the global population to experience widespread isolation and adopt practices such as ‘social distancing’ [7]. Many public health measures enacted during the pandemic exacerbated feelings of loneliness and social isolation [8], prompting calls for further investigations into their psychological, social, and economic impacts. Since the review by Mihalopoulos et al. [6] was conducted before the COVID-19 pandemic, we expected that additional economic studies examining the economic impacts of loneliness and social isolation and the value-for-money credentials of interventions targeting loneliness or social isolation had since been undertaken. Therefore, we aimed to update the previous review, following the same methodological evidence synthesis approach.

Methods

The original 2020 review was registered with the prospective register of systematic reviews, PROSPERO (CRD: 42018114749). This systematic review was reported according to the Preferred Reporting Items for Systematic Reviews and meta-analyses (PRISMA) 2020 guidelines for reviews [9]; the PRISMA reporting checklist is provided in the File 1 in the electronic supplementary material (ESM).

Search Strategy and Screening

Eligible cost-of-illness (COI) studies, economic evaluations, and return on investment (ROI) or SROI studies were identified by searching MEDLINE, CINAHL, PsycInfo (using Ebscohost platform), and Embase (using Elsevier) databases for articles published from 1 January 2018 to 13 August 2024. The search strategy, detailed in File 2 in the ESM and based on the original search, was structured around two thematic blocks. The first block included keywords and subject headings related to loneliness and social isolation, and the second focused on economics-related terminology (e.g. ‘economic evaluation’ or ‘cost of illness’). Boolean operators were applied, using ‘OR’ within each block and ‘AND’ between the two blocks. Limiters were set to include only peer-reviewed articles published in English from 1 January 2018 onward. All publications were imported into Covidence software [10], where duplicates were removed. Four reviewers (FR, SC, LE, and JF) screened the titles and abstracts. Reviewers examined the titles and abstracts based on the predefined inclusion and exclusion criteria described in Table 1. Any variation in decisions was resolved by LE. Three reviewers (FR, SC, JF) also assessed the articles accepted for full-text screening, and any variations were screened by LE. Hand searching was performed by checking the reference lists of the included publications, and the Scopus database was used to identify publications that had cited included publications.

Table 1.

Inclusion and exclusion criteria

	Inclusion criteria	Exclusion criteria
Population	All populations and age groups, including clinical groups	Animal studies
Design	Full economic evaluations, i.e. include both costs and outcomes/benefits of two or more alternatives. Cost-of-illness analysis (COI), e.g. healthcare expenditure. ROI, SROI	Health utilisation only (without reporting costs). Intervention comparisons with no cost evaluation
Intervention	Prevention or treatment of social isolation and loneliness. In case of a cost analysis, no intervention required
Outcome	Primary outcome of loneliness or social isolation	If loneliness or social isolation are a secondary outcome
Country	All countries
Method	Primary studies, reviews
Publication type	Peer reviewed or grey literature	Narrative reviews, expert opinion and editorials, qualitative studies, conference papers, dissertations, book chapters
Year of publication	1 January 2018 to 13 August 2024
Language	English	Languages other than English

COI cost of illness, ROI return on investment, SROI social ROI

Grey literature was identified using Google Advanced Search. Terms used included (loneliness OR lonely OR “social isolation” OR “socially isolated”) AND (cost OR “economic evaluation” OR “cost” OR “cost-effectiveness” OR “return on investment”); language was set as English; and site was set as any domain. Search strings were added to the “all these words” field, and the scope was narrowed using the “Then narrow your results by” fields of language, region, site or domain, terms appearing, and file type. Results were downloaded into a Microsoft Excel spreadsheet. Two reviewers (FR and SC) reviewed the first 100 results for each of the 10 domains, and one reviewer (LE) resolved any conflicts between reviewers. Broken links were excluded if an attempt at locating the correct link was unsuccessful.

Data Extraction and Synthesis

Study information was extracted into standardised tables separately for COI, economic evaluation, and ROI/SROI studies. LE extracted the data, which FR then checked. For COI studies, we extracted information on the country, year, and measure of loneliness or social isolation and recorded which cost categories were included by the respective study (i.e., outpatient care, inpatient care, medication, informal care, residential aged care, productivity, other). For economic evaluation studies, we extracted the following information: year, country, population/sample description, interventions, evaluation type (i.e., cost-effectiveness analysis [CEA], cost-utility analysis [CUA], cost-benefit analysis [CBA], study design (randomised controlled trial [RCT] or modelled), perspective, time horizon, reference year and discount rate, costs, outcomes, measure of loneliness or social isolation, and results). Finally, for SROI studies, we extracted information on the intervention, targeted population, stakeholders considered, data source, inputs, outcomes, reference year, time horizon, discount rate, and SROI ratio. To enable comparisons, costs reported were converted into US$, year 2024 values, using gross domestic product purchasing power parity (PPP) conversion rates for each country using the CCEMG–EPPI Centre Cost Converter [11].

We conducted a narrative synthesis structured by study type: COI, economic evaluation, and SROI studies. For COI studies, we distinguished between population-level estimates and those calculated per individual experiencing loneliness or social isolation. We synthesised the economic evaluation findings separately for model-based and trial-based evaluations to reflect differences in methodological approach. As in our previous review, although we initially planned to perform a meta-analysis to quantitatively pool results, this was not feasible because of the substantial heterogeneity in study designs, populations, interventions, and outcome measures. As a result, we deemed a quantitative synthesis inappropriate. For SROI studies, data were synthesized according to country and intervention type.

Quality Appraisal

To assess the quality of the studies included, we used different quality appraisal tools according to the type of study. For economic evaluation studies, we used the Drummond et al. [12] checklist, which comprises 10 questions and 33 sub-questions. We assessed COI studies using a checklist by Larg and Moss [13] that focuses on three domains: (1) the analytic framework, (2) methodology and data, and (3) analysis and reporting. We use da 12-point quality assessment framework for SROI studies by Krlev et al. [14] for ROI/SROI studies. Two reviewers (LE and FR) assessed all studies, and discrepancies were resolved via discussions.

Results

The bibliographic database search retrieved 2894 records. After screening abstracts and full texts, 11 papers were included. Additionally, four papers were identified from the grey literature search, bringing the total number of papers in the review to 15 (see Fig. 1). This included six COI studies, four economic evaluations, and five SROI studies. The studies were conducted in various countries, including the UK (n = 6), Australia (n = 4), the Netherlands (n = 2), USA (n = 1), Spain (n = 1), and Japan (n = 1).

Fig. 1.

PRISMA flow diagram

Cost-of-Illness Studies

Of the six COI studies (see Table 2), three provided population-based cost estimates [15–17], and three studies reported the cost per lonely or socially isolated person [18–20]. Four studies examined loneliness as an outcome: two studies using the University of California, Los Angeles (UCLA) 3-item Loneliness Scale [15, 20], one study used the 11-item De Jong Gierveld scale [17], and one used a single-item direct measure [16]. One study focused on social isolation, assessed with a two-item measure [19], whereas another study evaluated both loneliness and social isolation, using the UCLA 3-item Loneliness Scale for loneliness and an adapted version of the Social Network Index for social isolation [18]. Although five studies considered healthcare costs, only three studies examined productivity costs [15, 16, 20]. One study focused exclusively on child-rearing costs (e.g., food, clothing) among mothers with a 6-month-old baby in Japan [19]. One study examined the cost of loneliness and social isolation in older adults [18], and the remaining studies focused on the general population.

Table 2.

Study characteristics of cost-of-illness studies

Study, country	Loneliness or social isolation measure	Population	Year of costs, currency	Costs reported (original currency)	US$ (2024 PPP)a	Cost categories included (+)/not included (−)							Quality scoreb
						Primary care	Inpatient care	Medication	Informal care	Residential care	Productivity	Other
Population-based cost estimates
Casal et al. [15] (2024), Spain	Loneliness (UCLA 3-item)	Spain general population (15+ age)	2021, €	Healthcare: €6.1 bpa Productivity: €8.0 bpa Intangible cost (QALYs): $1 mpa Total: €14 bpa	$10.8 bpa $14.3 bpa $1.8 mpa $25.2 bpa	+	+	+	−	−	+	+c	91%
Duncan et al. [16] (2021), Australia	Loneliness (1-item measure)	General population	2021 assumed, A$	A$2.7 bpa (A$1565 pa pp)	$2 bpa ($1196 pa pp)	+	+	−	−	−	+	+d	39%
Meisters et al. [17] (2021), Netherlands	Loneliness (11-item de Jong Gierveld scale)	General adult (18+) population	2017, €	− €435.4 mpa	− $701 mpa	+	+	+	−	−	−	-	96%
Person-based cost estimates
Barnes et al. [18] (2022), USA	Loneliness (UCLA-3) and social isolation (adapted from Social Network Index)	Older adults	2020 assumed, US$	Lonely only: US$10,350 pp Socially isolated only: US$9476 pp Both: US$13,008 pp Neither: US$9292 pp	$12,270 $11,234 $15,421 $11,016	+	+	+	−	−	−	-	91%
Honda et al. [19] (2019), Japan	Social isolation (maternal social isolation, 2 questions)	Mothers with 6-mo-old baby	2001, JPY	JPY4186 per mo, pp (JPY 350m for entire population)	$45.92/mo pp $3.8 m	−	−	−	−	−	−	+e	96%
Peytrignet et al. [20] (2020), UK	Loneliness (UCLA 3-item + direct question)	UK general population	2019, £	Wellbeing cost: £6429 pp (mild), £8157 to £9537 pp (moderate), £9976 pp (severe) Productivity: £330 pp Health: £109 pp Total: £6429 (mild) to £9976 (severe)	$11,330 (mild), $14,375 to 16,808 (moderate), $17,581 pp (severe) $582 pp $192 pp $11,330 (mild) to $17,581 (severe)	+	+	−	−	−	+	+f	45%

$ dollar, £ pound, € Euro, A$ Australian dollar, bpa billion pa, JPY Japanese Yen, m million, mo month(s), mpa million pa, pa per annum, pp per person, PPP product purchasing power parity, QALYs quality-adjusted life-years, UCLA University of California Los Angeles, UK United Kingdom, US$ US dollar

^aThe CCEMG–EPPI Centre Cost Converter was used to convert cost estimates into $US, year 2024 values, using gross domestic PPP conversion rates for each country: https://eppi.ioe.ac.uk/costconversion/

^bQuality assessment was undertaken using Larg and Moss’s checklist

^cIntangible costs due to loss in QALYs due to reduced quality of life and premature deaths

^dCosts of unhealthy lifestyle behaviour (i.e., physical inactivity, regular smoking, and excessive alcohol use) associated with loneliness

^eNon-medical costs included child-rearing costs (food, clothing, etc.)

^fCosts stemming from impacts on subjective wellbeing

Most studies reported excess costs associated with loneliness or social isolation, ranging from US$2 billion per year in Australia [16] to US$25.2 billion per year in Spain [15]. Person-based annual estimates ranged from US$1196 per lonely person in Australia [16] to US$17,581 per severely lonely person in the UK [20]. However, a Dutch study found that, although higher expenditure was observed among lonely people than among non-lonely people for mental health and general practitioner (GP) spending, when adjusting for self-perceived health and psychological distress, loneliness was associated with lower total expenditure than the ‘not lonely’ reference group [17].

In an Australian study, annual economic costs associated with loneliness among the general population were estimated at A$2.7 billion (US$2 billion) or A$1565 (US$1196) per person. These estimates were derived by drawing comparisons between people who either become or remained lonely and those who did not in terms of productivity losses and unhealthy lifestyle, such as smoking, physical inactivity, alcohol consumption, and higher number of GP and hospitalisation visits [16]. Casal et al. [15] examined healthcare costs, productivity costs, and intangible costs because of quality-adjusted life-year (QALY) losses among the general population in Spain, with annual costs estimated at €6.1 billion (US$10.8 billion), €8.0 billion (US$14.3 billion), and €1 million (US$1.8 million), respectively [15]. The total costs were estimated at €14 billion (US$25.2 billion). Barnes et al. [18] examined the costs of both lonely and socially isolated older adults in the USA, finding that participants who were lonely had higher medical costs (US$12,270) than those who were socially isolated (US$11,234) and that those who were both lonely and socially isolated had the highest total medical costs (US$15,421) [18]. A UK study differentiated between annual costs associated with mild and severe loneliness, which were estimated retrospectively at £6429 (US$11,330) and £9976 (US$17,581). These included healthcare costs, productivity costs, and wellbeing costs, where the wellbeing impacts of alleviating loneliness were converted into monetary terms using the wellbeing valuation method [20]. The final study, conducted in Japan, estimated the child-rearing costs among mothers of a 6-month-old baby and found that isolated mothers spent JPY4186 (US$46) more per month than non-isolated mothers [19].

Economic Evaluations

Of the four economic evaluations (Table 3), three were modelled evaluations [21–23] and one was conducted alongside an RCT [24]. The latter evaluated the cost effectiveness of the positive psychology intervention ‘Happiness Route’ in the Netherlands, focusing on individuals aged ≥ 18 years who were lonely, experienced health problems, and had a low income [24]. Although loneliness decreased in both the intervention and the control groups, the difference between groups was not statistically significant. The intervention was associated with fewer QALYs and fewer costs, resulting in an incremental cost-effectiveness ratio (ICER) of €161,953 (US$247,063 equivalent), suggesting that the probability of the intervention being cost effective was 54% at a willingness-to-accept threshold for QALY losses of €100,000 (US$152,552 equivalent). Two modelled studies targeted older adults who experienced loneliness: McDaid and Park (2021) evaluated a local signposting service to help older adults make new connections [23], and Engel et al. [22] evaluated the Friendship Enrichment Programme and a volunteer-led internet and computer training intervention. Both studies used a Markov model with a 5-year time horizon. The incremental cost per loneliness-free year of the signposting intervention was £768 (US$1353 equivalent), but the probabilistic sensitivity analysis showed that the intervention was cost saving in only 3.5% of the bootstrapped iterations [23]. The Friendship Enrichment Program and volunteer-led internet and computer training were both more effective and less costly than a ‘no intervention’ scenario. However, uncertainty was high, with only 55% and 68% of uncertainty iterations lying below the A$50,000 (US$44,415 equivalent) per QALY gained willingness-to-pay threshold for the Friendship Enrichment Program and volunteer-led internet and computer training, respectively [22]. The study also calculated the ROI for both interventions, which were estimated to be A$2.87 (US$2.55 equivalent) for the Friendship Enrichment Program and A$2.14 (US$1.90 equivalent) for the volunteer-led internet and computer training. The final study, by Beilby et al. [21], modelled the cost effectiveness of Neighbour Day, which is Australia’s annual community development campaign with a focus on inclusion and connection and reducing loneliness. In the absence of a control group, the study used data from a national survey (i.e., Household, Income and Labour Dynamics in Australia) and applied matching techniques to create a control cohort. The study found that the ICER was AU$4667 (US$3793 equivalent) per QALY gained and A$141 (US$115 equivalent) per loneliness-free year, suggesting it was cost effective adopting a willingness-to-pay threshold of A$28,033 (US$22,783 equivalent) per QALY gained [21].

Table 3:

Study characteristics of economic evaluations

Study, country	Population/sample description	Intervention(S) and comparator	Evaluation type	Study design	Perspective, time horizon	Reference year, discount rates	Costs	Outcomes	Measure of loneliness/social isolation	Results (US$, 2024 PPP)	Quality scorea
Beilby et al. [21] (2023), Australia	General population	Neighbour Day (Australia's annual celebration of community event) vs matched control group	CUA CEA	Modelling	NR	NR (2019 assumed)	Intervention cost, GP visits, hospitalization	QALYs, loneliness-free year	1-item loneliness measure	CUA: ICER: A$4,667 (US$3793) per QALY gain CEA: ICER: A$141 (US$115) per loneliness-free year	75%
Engel et al. [22] (2021), Australia	Lonely older adults, lonely older women	FEP and a volunteer-led VICT intervention vs no intervention	CUA ROI	Modelling	Societal and healthcare, 5 y	2016; 3% for costs and QALYs	Intervention cost, cost savings (physician consultation, hospitalisation, depression treatment, productivity gains)	CUA: QALYs ROI: cost savings	6-item and 11-item de Jong Gierveld scale	CUA: FEP: 55% under WTP threshold; VICT: 68% under WTP threshold. ROI of $2.87 (US$2.55) for FEP and $2.14 (US$1.90) for VICT	86.67%
McDaid and Park [23] (2021), UK	Lonely people aged ≥65 y	Signposting services vs no intervention	CEA	Modelling	Health and social care perspective; 5 y	2019; 3.5% for costs and 1.5% for outcomes	Intervention cost, cost savings (ED; hospital admission, GP, residential care, ambulance; cost due to coronary heart disease, dementia, depression, stroke; self-harm treatment)	Loneliness-free year gained	UCLA Loneliness scale	ICER: £768 (US$1353) per loneliness-free year gained (3.5% cost saving)	68.97%
Weiss et al. [24] (2020), Netherlands	Lonely individuals with health problems and low income	Happiness Route (PPI) vs active control (customized care)	CUA	Randomised, single-blind, actively controlled, parallel-group study	Healthcare perspective, 12 mo	Year NR (2019 assumed); no discounting	Intervention cost, medical care consumption, informal care costs	QALYs	De Jong Loneliness Scale	Intervention resulted in fewer QALYs and higher costs. ICER: €161,953 (US$247,063) 83% that the Happiness Route was cost saving and 54% that the Happiness Route was cost effective at a WTA threshold of €100,000	55.17%

$ dollar, £ pound, € Euro, A$ Australian dollar, CEA cost-effectiveness analysis, CUA cost-utility analysis, ED emergency department, FEP Friendship Enrichment Programme, GP general practitioner, ICER incremental cost-effectiveness ratio, mo month(s), NR not reported, PPI positive psychology intervention, PPP product purchasing power parity, QALYs quality-adjusted life-years, ROI return on investment, U$ US dollar, UCLA University of California, Los Angeles, UK United Kingdom, VICT volunteer-led internet and computer training, WTP willingness to pay, y year

^aQuality assessment was undertaken using the Drummond et al. [12] checklist for the critical assessment of economic evaluation

SROI Studies

Five SROI studies were identified (Table 4): four were conducted in the UK [25–28] and one was in Australia [29]. Three studies [25, 27, 29] presented a ‘theory of change’ map, illustrating how inputs were used to produce outputs that resulted in outcomes, which is central to SROI analysis. Bosco et al. [25] evaluated the Imagine Arts programme, focused on the delivery of high-quality arts interventions among care home residents in the UK. Based on interviews, diaries, and quarterly reports, they calculated an SROI of £1.20 (US$2.28) for every £1 (US$1.90) invested, with sensitivity analysis identifying estimates ranging from 0.08 to 1.19 [25]. A social prescribing programme was evaluated, where a link worker helped service users access appropriate support such as community activities and social groups. The study found that 72.6% of service users felt less lonely after receiving support, and the mean change in UCLA 3-item Loneliness Scale score was − 1.84 (95% confidence interval − 1.91 to − 1.77). The SROI was estimated at £3.42 (US$6.02), which remained robust in the sensitivity analyses (ratios ranged between 2.40 and 4.45) [26]. Jones et al. [27] assessed the SROI of a social prescribing physical activity programme (the Health Precinct) for community-dwelling people with chronic conditions aged ≥ 55 years. Data via postal questionnaires were collected at baseline and 16-week follow-up to quantify change. In total, £281,010 of social value was generated by the Health Precinct in a 1-year period, resulting in an SROI of £5.07 (US$9.12) (sensitivity analysis ratios ranged between 2.60 and 5.16) [27]. Willis et al. [28] evaluated three dementia support groups and found SROIs ranging from £1.17 to £5.18 (US$3.10–13.72). The intervention increased mental stimulation and reduced loneliness and isolation in people with dementia, reduced stress for carers, and increased knowledge in volunteers [28]. The final Australian study evaluated a programme that supported people experiencing a crisis to access boarding and veterinary treatment for their animals. Questionnaires were used to understand the social value created by the programme, and 13 stakeholders were interviewed. The strongest benefit of the programme was attributed towards preserving the human–animal bond and to improvements in the mental health and wellbeing of both humans and animals, alongside reducing loneliness. The SROI was AU$8.21 (US$6.27), suggesting that the programme provided a considerable ROI [29].

Table 4.

Study characteristics of SROI studies

Study, country, ROI/SROI	Intervention, target population	Target population	Stakeholders considered	Data source for evidencing outcomes	Inputs	Outcomes	Year of pricing, time horizon, discount rate	SROI ratio obtained	Quality scorea
Bosco et al. [25], 2019, UK, SROI	Imagine Arts programme	Care home residents	Care home residents, care home personnel, and activity coordinators	Quarterly reports, diaries, Interviews	Knowledge and time of artists, digital aids and room space, support from carers and activity coordinators, monetary funding from Baring foundation and City Arts, in-kind support from City Council, older people time and creativity	Decreased social isolation; improved quality in mental health, mobility, community inclusion, and cognition for older people Increased skills and confidence in using arts intervention for artists, care home personnel and activity coordinators; increased publicity for care home providers	2014 to 2015; 4 y; 3.5% discount rate	£1.20 (US$2.28) for every £1 expenditure. Sensitivity analysis: SROI ranged from £0.08 to £1.19 (US$2.26)	83.33%
Foster et al. [26] (2020), UK, SROI	Social prescribing programme (British Red Cross)	Service users (≥ 18 y referred to service)	Service users, managers, link workers, volunteers, representatives from funders	Surveys (UCLA questionnaire), workshop, discussions with stakeholders, routine data and interviews	Cost of volunteers	Service users’ wellbeing; avoided missed health appointments; value of volunteers	2018 to 2019; 30 mo; 3.5% discount rate	£3.42 (US$6.03) per £1 invested. Sensitivity analysis: SROI ratio range £2.40 (US$4.23) to £4.45 (US$7.84)	83.33%
Jones et al. [27] (2020), UK, SROI	Health Precinct (16-wk physical activity programme)	People with chronic conditions aged ≥ 55 y living at home	People with chronic conditions aged ≥ 55 y, participants’ families, staff, NHS, and local government	Postal questionnaires	Attendance fees, staffing, equipment, overheads	Increased physical activity; improved health status; higher confidence; increased social connection. Family: improved health status. NHS Wales: reduced GP attendances. Council: Increased leisure centre membership	2018; 1 y; 3.5% discount rate	£5.07 (US$9.12) of social value generated for every £1 invested. Sensitivity analysis yielded estimates between 2.60:1 and 5.16:1	83.33%
Ma et al. [29] (2023), Australia, SROI	RSPCA NSW emergency; boarding and homelessness programme	Pet owners experiencing a crisis (homelessness, mental illness)	Programme clients, client’s animals, RSPCA inspectors, animal pounds, and shelters	Interviews and questionnaires	Cost of the RSPCA NSW emergency boarding programme	Clients: Improved mental health and wellbeing; extended human–animal bond; improved personal safety; increased social inclusion, decreased isolation; improved physical health; decreased financial stress. Seven other outcomes for animals, inspectors, and shelters	2020 to 2021; 3 y; no discount rate mentioned	A$8.21 (US$6.27) for each A$1 invested	75%
Willis et al. [28], (2018), UK, SROI	Three dementia peer support groups	People with dementia and their carers	People with dementia, carers, volunteers	Interviews, focus groups,	Volunteers’ time and venue hire	People with dementia: reduced loneliness and isolation, mentally stimulated. Carers: reduced stress and burden. Volunteers: increased sense of wellbeing and level of knowledge	No reference year (2017 assumed); 1 y; no discounting	£1.17 (US$3.10) to £5.18 (US$13.72) for every £ invested	66.67%

$ dollar, £ pound, A$ Australian dollar, GP general practitioner, mo month(s), NHS national health service, NSW New South Wales, ROI return on investment, RSPCA The Royal Society for the Prevention of Cruelty to Animals, SROI social return on investment, UCLA University of California, Los Angeles, UK United Kingdom, US$ US dollar, wk week, y year

^aQuality assessment was undertaken using the 12-point quality assessment framework for social return on investment studies by Krlev et al. [14]

Quality of Studies

Quality appraisal results are available in file 3 in the ESM. Three COI studies achieved a quality score above 90% [15, 17, 19], one scored 61% [18], and two scored below 50% [16, 20]. The latter two, derived from the grey literature search, lacked detailed cost measurement and valuation information and did not conduct sensitivity analyses or report uncertainty around estimates and its implications. However, study quality did not appear to influence the findings, as there were no clear trends or patterns in the reported cost estimates based on quality ratings. The quality scores of economic evaluation studies ranged from 55 to 87%. Three studies had reduced scores because they did not cover all relevant perspectives or identify all possible alternatives [21, 23, 24]. Additionally, none accounted for heterogeneity in results, conducted subgroup analyses, or discussed the generalisability of their findings. SROI studies were generally of good quality, with scores ranging from 67 to 83%. Score deductions primarily stemmed from the absence of a control group or failure to perform an ex-ante/ex-post observation scenario, and two studies did not conduct sensitivity analyses [28, 29]. However, the heterogeneity of the interventions assessed means it is not possible to determine the extent to which the quality scores of the economic evaluation and SROI studies may have contributed to conflicting or inflated findings.

Discussion

Building on a previous review that identified 12 studies [6], our updated literature review found 15 additional studies published within the last 6 years, reflecting the growing research interest in the economic impact of loneliness and social isolation. This increase in studies suggests an increasing recognition of loneliness as a public health and economic concern, prompting further investigation into its associated costs and the cost effectiveness of interventions. Despite the increase in studies, our updated review showed that most studies continue to target older adults. This was observed in the initial review, highlighting a significant knowledge gap in groups other than older adults. Studies conducted among young adults are particularly lacking, despite loneliness being as common among young adults as in older adults [30]. Another key observation is that all studies were conducted in high-income countries, predominantly in the UK. Loneliness research has largely been driven by high-income nations, and the lack of data from low- and middle-income countries has been recognised as an important equity issue [31]. There has been a notable increase in COI studies, with new cost estimates reported for countries such as Spain, Australia, the Netherlands, and Japan. This review also identified an additional COI study from the UK, which, for the first time, considered wellbeing costs and reported costs based on levels of loneliness [20]. All SROI studies included in this review assessed new interventions, but one study provided additional cost-effectiveness insights into the Friendship Enrichment Program and volunteer-led internet and computer training interventions that had been previously reviewed [22], supporting findings by Mallender et al. [32].

Our review identified six COI studies that highlighted the economic impact of loneliness and social isolation. Although all except one study [19] included healthcare costs, only three studies considered productivity costs, and only one study included presenteeism (i.e., reduced productivity at work) [20]. Two studies considered further intangible costs (expressed in loss of QALYs) [15] and wellbeing costs [20]. None of the studies focusing on older adults examined residential aged care costs, despite evidence showing that loneliness is a risk factor for care home admissions [33]. Additionally, informal care costs have not been considered by any studies, although loneliness can significantly increase informal care costs because of its association with worsened health outcomes and greater dependence on caregivers [34]. Additionally, informal carers themselves are more prone to loneliness [35]. Overall, the economic cost estimates reported in the literature are likely to be an underestimate as broader costs to individuals and our society, including foregone lifetime earnings due to worse educational and employment outcomes, have not been explored [36]. Omitting these broader economic consequences risks underestimating the true burden of loneliness and social isolation and may limit the relevance of COI findings for policy development. Where comprehensive data are lacking, COI studies should, at a minimum, acknowledge these limitations and highlight intersectoral costs as an important area for future research.

Further, most of the COI studies adopted a cross-sectional design, which limits the identification of causal relationships. Given the bi-directional relationship between loneliness and certain chronic conditions [37], longitudinal studies are needed to shed more light on whether loneliness leads to chronic conditions that lead to an increase in estimated costs or whether those who experience a chronic condition have elevated levels of loneliness, which in turn drives additional costs. Furthermore, potential mediators, such as alcohol and tobacco use, physical inactivity, and poor diet, complicate the pathways through which loneliness and social isolation contribute to chronic illness and its downstream cost consequences. These lifestyle factors are not only health outcomes in themselves but also behavioural responses that can amplify or obscure the impact of loneliness or social isolation. We identify this as a critical gap in the current literature and recommend further empirical research to quantify the role and cost implications of these behavioural mediators. In practice, we suggest future studies to present COI estimates with and without these potential behavioural mediators. Another important consideration is the necessity of controlling for confounders. Only Meisters et al. [17] controlled their cost analysis for potential confounders (demographic, socioeconomic, lifestyle-related factors, self-perceived health, and psychological distress), and their results showed that the positive association between loneliness and expenditure reversed when self-perceived health and psychological distress (using the Kessler psychological distress scale) were controlled for. Based on this finding, the authors emphasized that loneliness may influence healthcare expenditure through various pathways, including deteriorating self-perceived health and increased psychological distress.

Of the four economic evaluations, three modelled studies concluded that the interventions examined were likely cost effective. These included the Friendship Enrichment Program and volunteer-led internet and computer training [22], signposting [23], and Neighbour Day in Australia [21]. The only economic evaluation conducted alongside a trial noted that the positive psychology intervention (Happiness Route) resulted in fewer QALYs but possible cost savings [24]. However, the authors highlighted that how to interpret the results of disinvestment remained unclear given the lack of empirical studies examining the willingness-to-accept threshold for QALY losses in the Netherlands [24]. It is important to note that the two modelling studies adopted a time horizon of 5 years, which is considerably longer than the 1-year time horizon adopted in the RCT, suggesting that modelling can offer advantages in evaluating long-term outcomes and costs (although the robustness of such extrapolated impact will depend on the quality of evidence informing them). Modelling relies on effectiveness evidence, and the current evidence base for many interventions is lacking in terms of low-quality trials, small samples, lack of theoretical frameworks or understanding of loneliness, diverse undefined target groups, mixed measures of loneliness, and short follow-up periods [38]. A further observation from our review was that most economic evaluations were CUAs, using QALYs as the main measure of outcome. Although these studies used the EQ-5D and Short Form 6-Dimensions (SF-6D) measures to derive QALYs, little attention was paid to the choice of utility measure, with a previous review suggesting that utility values associated with loneliness and social isolation vary according to the choice of measure [39], which can influence cost-effectiveness results. Only one study calculated the cost per loneliness-free year gained [23], but in the absence of a cost-effectiveness threshold for improvements in such an outcome, QALYs (which are also recommended by many health technology assessment bodies) appear more suitable to facilitate comparisons. All economic evaluation studies considered healthcare costs (i.e., physician consultations, hospitalisations) in their evaluations, two modelled studies considered the costs of depression, which can be caused by loneliness [22, 23], and one study also considered costs of coronary heart disease, dementia, and stroke [23]. Productivity costs were often excluded, with the exception of Engel et al. [22], who recognised that although many older adults are no longer part of the active labour force, some continue working, and productivity costs were therefore considered. Only Weiss et al. [24] considered informal care costs, despite their importance among older adults and social care users, which can affect cost-effectiveness findings [40]. Including costs beyond the healthcare sector becomes particularly important in the context of loneliness interventions delivered outside of the healthcare system, such as school-based programmes or community engagement initiatives. To facilitate comparisons in future studies, there is an urgent need for standardised methods in economic evaluations, particularly with respect to including intersectoral costs, capturing costs associated with chronic conditions linked to loneliness, and refining measurement approaches.

Our updated review has further confirmed the growing interest in conducting SROI studies in this field, with four studies included in our review conducted in the UK. SROI studies are sometimes preferred over traditional health economic evaluations in this context because they provide a broader, more holistic assessment of the value a programme or intervention is generating [41]. This is because they allow the consideration of outcomes that go beyond health (e.g., social, economic, and environmental outcomes) and that affect multiple stakeholders (e.g., patients, carers, communities). SROI studies further place a monetary value on benefits that are considered difficult to value monetarily, such as social cohesion. Furthermore, SROI typically does not require a control group because it relies on stakeholder-informed impact measurement and valuation techniques rather than experimental designs. Instead, SROI uses counterfactual estimation, deadweight adjustment, and attribution analysis to adjust the impact [42]. Given these perceived benefits, two SROI studies in this review explicitly justified their decision to use an SROI framework instead of a traditional economic evaluation [27, 28]. However, because of the weak attribution, where a direct cause-and-effect relationship between an intervention and its outcomes cannot be established in SROI studies, and the inability to make comparisons across different health interventions due to different valuation studies, SROI studies cannot be used for economic evaluation. Additionally, it is important to note that SROI studies make it difficult to isolate the economic return specifically attributable to improvements in loneliness or social isolation, as the SROI ratio reflects the combined social value of all reported outcomes. This limitation should be taken into account when interpreting the findings.

Determining an appropriate evaluation framework for interventions targeting loneliness or social isolation requires more nuanced consideration. Interventions addressing loneliness or social isolation can be categorised into three categories: (1) individual- and relationship-level interventions (e.g., one-to-one or group interventions, digital and face-to-face interventions) focusing on maintaining and supporting people’s relationships and changing how people think and feel about them; (2) community-level strategies addressing infrastructures such as transportation, digital inclusion, and the built environment; and (3) societal-level strategies that include laws and policies, such as increasing social cohesion and reducing marginalization [43]. Although traditional economic evaluation frameworks (i.e., CEA, CUA, CBA) appear suitable for the evaluation of individual- and relationship-level interventions, it is likely that different evaluation frameworks may be required for community-level and societal-level strategies. Such interventions in a way can be considered complex interventions that contain multiple interacting components either within the intervention itself, in the delivery context, or in the way outcomes are produced. Different evaluation frameworks have been proposed for complex interventions, with some recommending the use of multiple criteria decision analysis [44] or discrete choice experiments to identify a set of attributes for complex interventions and to establish values for those attributes [45], whereas others suggested CBA or cost-consequence analysis, which seek to capture the full range of health and non-health costs and benefits across different sectors [46]. Although diversity and complexity of loneliness and social isolation interventions are acknowledged, the absence of a consistent evaluation framework poses challenges for equitable and evidence-based decision-making. The evaluation of complex interventions may necessitate moving beyond individual-reported data toward system-level data collection and the incorporation of modelling approaches. Future research is needed to establish a standardised yet adaptable evaluation framework to guide policy and resource allocation decisions.

Limitations of the Review

This review has several limitations that should be acknowledged. First, we did not include studies that exclusively examined health service use, which may have limited our understanding of the broader economic and healthcare implications of loneliness and social isolation. Second, our inclusion criteria focused only on studies where loneliness or social isolation was the primary outcome, potentially overlooking relevant studies that assessed these factors as secondary outcomes. Additionally, the use of different quality assessment checklists across studies restricted our ability to systematically compare study quality. Another limitation is that we only included articles published in English, which may have excluded relevant non-English studies. Finally, while our review focused specifically on loneliness and social isolation, we did not include studies on related concepts such as social support and social inclusion. Future research should consider these related constructs to provide a more comprehensive understanding of their economic impacts.

Conclusion

This review emphasises the growing evidence on the economic burden of loneliness and social isolation, highlighting significant healthcare and productivity costs. Although existing economic evaluations suggest that some interventions may be cost effective, findings remain mixed, with limited studies addressing broader societal costs. SROI analyses indicate positive returns, underscoring the potential value of addressing loneliness through targeted interventions. However, further research is needed to capture costs beyond the healthcare sector, including education and informal care costs, and to evaluate interventions across diverse communities, including children and adults. Expanding economic analyses in this field will be crucial for informing policy decisions and resource allocation aimed at mitigating the widespread impact of loneliness and social isolation.

Supplementary Information

Below is the link to the electronic supplementary material.

Declarations

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.

Availability of data and materials

The authors confirm that all data generated or analysed during this study are included in this article and its electronic supplementary files.

Compliance with ethical standards

Not applicable.

Funding

Open Access funding enabled and organized by CAUL and its Member Institutions. This work was partly funded by the National Health and Medical Research Council (NHMRC) Targeted Call for Research (TCR): Loneliness, Social Isolation and Chronic Disease Management (#2024805).

Author contributions

All authors contributed to the study conception and design. FR and SC performed the literature search, and LE, FR, SC, and JF performed the screening process. LE and FR extracted and appraised the quality of the data. LE wrote the initial draft of the manuscript, all authors commented on subsequent versions and read and approved the final manuscript.