Table 2 Summary of included articles, by alphabetical order of first author

Balto J, et al. (2018) [31]

Study design: Quantitative – cross-sectional, comparative study, age 18–64 years

Data collected as part of another study examining measures of aerobic and muscular fitness in persons with multiple sclerosis compared with healthy adults

Recruitment: North American Research Committee on multiple sclerosis registry and author lab database

Country: Illinois, United States of America

Study dates: Not stated

Multiple sclerosis

Determination: Registration on research register

Sample size: Multiple sclerosis n = 63; comparison n = 21

Definition: Perlman and Peplau (1981) [32]

Measurement: Original UCLA-LS 20-Item Scale

Hospital Anxiety and Depression Scale [33]—Measures the frequency of anxiety and depression symptoms over the past 4 weeks

Modified Fatigue Impact Scale [34]—Examines patients’ perceptions of the functional limitations that fatigue has caused over the past month

Multiple Sclerosis Impact Scale-29 (MSIS-29) [35] -

Provides a measure of the physical and psychological impact of multiple sclerosis from the patient’s perspective (i.e., Quality of Life)

Depression, fatigue (both cognitive and psychosocial), and psychological quality of life were correlates of loneliness for people with multiple sclerosis

Anxiety, physical fatigue, physical quality of life was not associated with loneliness for people with multiple sclerosis

Chang Y, et al. (2019) [36] + 

Study design: Quantitative – cross-sectional survey, comparative study, age 10–19 years

Primary data collection: survey mailed, self-administered

Recruitment: Via flyers, e.g., in mainstream high schools, autism groups and via social media

Country: Taiwan

Study dates: Not stated

Autism spectrum disorder

Determination: Independent diagnosis of autism spectrum disorder

by a registered psychiatrist

Sample size: Autism spectrum disorder n = 101; comparison n = 101

Definition: Not stated

Measurement: UCLA-LS 3-Item Scale (Chinese version)

Beck Anxiety Inventory (Chinese version) [37]- Measure of anxiety severity

Loneliness was significantly associated with greater anxiety among adolescents with autism spectrum disorder

Emerson E, et al. (2021) [9]

Study design: Quantitative – cross-sectional design, comparative study, age 16–64 years

Secondary analysis of population-level data from national survey

English Community Life Survey

Online completion of survey

Data were combined across three rounds of the Community Life Survey

Country: United Kingdom

Study dates: 2016–2019

Disability as a composite group

Determination: Positive response to two questions in Community Life Survey

Sample: Total n = 17,723 (2016–2019)

Average prevalence of disability, 19.1% (2016–2019)

Definition: Hawkley and Cacioppo (2010) [38]

Measurement: Single item developed by UK Office for National Statistics

Four indicators of personal wellbeing developed by the UK Office for National Statistics: Satisfaction, Worth, Happiness, Anxiety. [39]

Loneliness had a significantly greater association with poorer personal wellbeing outcomes of satisfaction, worth, happiness and anxiety for people with disability

Emerson E, et al. (2021) [10]

Study design: Quantitative – cross-sectional-design, comparative study, aged 16–64 years

Secondary analysis of population-level data from United Kingdom’s main annual household panel study national survey, Understanding Society

Computer-assisted personal interviewing and computer-assisted self-completion

Study location: United Kingdom

Study dates: Wave 8 (2016–2018) and Wave 9 (2017–2019) though loneliness data only available in Wave 9

Disability as a composite group. Created four-category variable (No disability; Disability offset; Disability onset; Persistent disability)

Determination: Positive response to two questions in Understanding Society survey

Sample: Wave 9 – 34,959 individuals in total; 76.6% reported no disability

Definition: Hawkley and Cacioppo (2010) [38]

Measurement: UCLA-LS 3-Item scale plus single item developed by UK Office for National Statistics

12-Item Short Form Survey (SF-12) [40]- Measure of mental and physical functioning over the past 4 weeks

12-Item General Health Questionnaire (GHQ-12) [41]- Measure for screening for the onset of common mental health problems associated with depression, anxiety, somatic symptoms and social dysfunction

Loneliness was associated with the incidence and prevalence of mental health problems, but not the prevalence of physical health problems, for people with disability

Papagavri K, et al. (2020) [42]

Study design: Quantitative – cross-sectional design, comparative study, aged 16 + years

Data from the population-level survey, Adult Psychiatric Morbidity Survey

Trained interviewers, face-to-face computer-assisted interviewing, and self-completion, also using a computer. Assistance provided where necessary

Study location: England

Study dates: 2014

Borderline intellectual impairment

Determination:

Intellectual functioning measured using the National Adult Reading Test. Those with IQ below 80 were identified as having borderline intellectual impairment

Sample: Borderline intellectual impairment n = 671; comparison n = 6206

Definition: Perlman and Peplau (1981) [32]

Measurement:

One item from the Social Functioning Questionnaire

14-Item Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS) [43]—Measure of mental and physical functioning over the past four weeks – a quality of life measure

Clinical Interview Schedule Revised (CIS-R) [44]—Measure to identify common mental disorders (depression, generalised anxiety disorder, agoraphobia, any phobia and panic disorder) who had been diagnosed and treated in the last 12 months

Self-harm and suicide – bespoke measure used to identify if participants had thought about suicide in the last week and the last 12 months

Physical health—bespoke measure to identify if participants had suffered from any of the following chronic diseases in the last 12 months: asthma, cancer, epilepsy, diabetes and high blood pressure

Self-reported health – bespoke measure using one item: “how is your health in general?”

Those with borderline intellectual functioning who reported feeling lonely had lower wellbeing, were more likely to have depression, generalised anxiety disorder, agoraphobia and any type of phobia in the last 12 months, and to report suicidal thoughts in the past week and last year than those with borderline intellectual impairment who were not lonely. Loneliness was also associated with chronic diseases and poor self- reported health

Robinson-Whelen S, et al. (2016) [45]

Study design: Quantitative – cross-sectional survey. Data drawn from an existing longitudinal cohort study. Participants originally recruited between 1973 and 2011 during initial post-injury rehabilitation in hospital. Current study includes participants who completed a follow-up survey, therefore 5–40 years follow-up

Study location: United States of America

Study dates: April 2014–June 2015 (for follow-up survey)

Spinal cord injury – level of injury represented by paraplegia versus tetraplegia

Determination:

Former patient at a spinal cord post injury rehabilitation centre

Sample: n = 175 with 58% tetraplegia, 39% paraplegia

Definition: Perlman and Peplau (1981) [32]

Measurement: UCLA-LS 3-Item Scale

Patient Health Questionnaire-2 (PHQ-2) [46]- Measure to identify individuals with elevated depressive symptoms

5-Item Satisfaction with Life Scale [47]—Measure to identify life satisfaction

Loneliness was significantly related to life satisfaction and depression for people with a spinal cord injury

Santino N, et al. (2022) [48]

Study design: Quantitative – cross sectional survey. Data collected as part of a larger study examining issues of social isolation and health in people with spinal cord injury or dysfunction. Telephone survey

Study location: Toronto, Canada

Study dates: Not stated

Spinal cord injury or dysfunction. Level of injury represented by paraplegia versus tetraplegia

Determination: Former patient at spinal cord rehabilitation program

Sample: n = 170 with traumatic and non-traumatic with spinal cord injury or dysfunction

Definition: Perlman and Peplau (1981) [32]

Measurement: UCLA-LS 3-Item Scale

11-Item Life Satisfaction Questionnaire (LiSat-11) [49]—Measure to identify life satisfaction

Significant bivariate correlations were found between loneliness and life satisfaction for people with a spinal cord injury or dysfunction

Smith B and Caddick N. (2015) [50]

Study design: Qualitative study. Aged 18 + years

Primary data collection, semi-structured life story interview. Criterion based, purposive sampling strategy. Open letter in United Kingdom disability newsletters and Internet sites

Study location: United Kingdom

Study dates: Not stated

Spinal cord injury

Determination: Registered as disabled by a United Kingdom Government authority

Sample: n = 20 with spinal cord injury, 14 lived in a care home and 6 lived in community. Sample size determined by data saturation

Definition: Not stated

Measurement: Qualitative inductive analysis

Qualitative responses

A theme in this qualitative study was that loneliness was perceived to damage psychological wellbeing for people with a spinal cord injury

Tough H, et al. (2017) [51]

Study design: Quantitative – cross sectional survey, aged 30–65 years. Data from existing longitudinal cohort study, namely the community survey of the Swiss Spinal Cord Injury Cohort Study. Standardised telephone interviews and questionnaires (paper–pencil or online)

Study location: Switzerland

Study dates: May 2015–January 2016

Spinal cord injury, traumatic and non-traumatic

Determination: Registration on research register

Sample: n = 133 with spinal cord injury; n = 133 partners of the persons with spinal cord injury

Definition: Hawkley and Cacioppo (2010) [38]

Measurement: UCLA-LS 3-Item

36-Item Short Form Health Survey (SF-36 version 1.0) [52]—Measure to identify vitality and mental health

For people with spinal cord injury who reported feeling lonely, this was associated with feelings of decreased vitality and poorer mental health for people with a spinal cord injury