Table 1.

Individual-level predictors of loneliness

Predictor	Key findings	Exemplary studies	Study description
Personality traits	Extraversion and emotional stability are linked to a lower risk for loneliness. Extraverted people are more likely than introverted people to seek out social interactions and to make friends. Emotionally stable people are less likely than emotionally unstable people to experience being alone as adverse.	Buecker et al. (2020)34	Meta-analysis (N = 93,668 individuals, k = 1,697 effect sizes) of relations between loneliness and Big Five personality traits.
Gender	Empirical findings on gender effects are inconsistent across single studies. Meta-analytic evidence shows that gender differences are small to negligible.	Maes et al. (2019)160	Meta-analysis (N = 399,798 individuals, k = 751 effect sizes) of gender differences in loneliness across the lifespan
Age	Old age (80+ years) tends to be associated with a significant increase in loneliness, mostly owing to widowhood, poor health and reduced mobility in this age group. Age is not a risk factor for loneliness itself, as loneliness can be experienced by people of any age, and some risk factors are specific to certain age groups.	Mund et al. (2020)25	Meta-analysis of longitudinal studies (N = 83,667 individuals, k = 208 effect sizes) on the development of loneliness across the lifespan
		Qualter et al. (2015)24	Theoretical article providing a lifespan perspective on the emergence and development of loneliness
		Luhmann & Hawkley (2016)18	Nationally representative study from Germany (N = 16,132) on age differences in loneliness from late adolescence to old age
Socioeconomic status	Being unemployed and having a low income are associated with a greater risk of loneliness because financial resources are often required to participate in everyday social activities.	Cohen-Mansfield et al. (2016)19	Systematic literature review (k = 38 articles) of correlates and predictors of loneliness in old age
Household composition	People living alone tend to feel lonelier, but this effect can mostly be explained by differences in marital status and income.	Luhmann & Hawkley (2016)18	Nationally representative study from Germany (N = 16,132) describing sociodemographic correlates of loneliness across the lifespan
Health	Poor health and functional limitations restrict people’s opportunities to participate in everyday social activities and can therefore lead to social isolation and loneliness.	Cohen-Mansfield et al. (2016)19	Systematic literature review (k = 38 articles) on correlates and predictors of loneliness in old age.
		Dahlberg et al. (2022)20	Systematic literature review (k = 34 articles) on longitudinal risk factors for loneliness in old age.
Relationship status	People who are single have a greater risk of loneliness than people in stable relationships, but some people feel lonely despite having a partner. Getting divorced or becoming widowed is associated with immediate and lasting increases in loneliness.	Cohen-Mansfield et al. (2016)19	Systematic literature review (k = 38 articles) on correlates and predictors of loneliness in old age.
		Dahlberg et al. (2022)20	Systematic literature review (k = 34 articles) on longitudinal risk factors for loneliness in old age.
		Hsieh & Hawkley (2018)161	Nationally representative study of older adults in the USA (N = 3,005) using data from romantic couples.
		Buecker et al. (2021)49	Nationally representative longitudinal study from the Netherlands (N = 13,945) on changes in loneliness surrounding different major life events.
Social isolation	People who have small social networks and few social interactions are more likely to feel lonely, but loneliness (perceived social isolation) and (objective) social isolation are not the same.	Cohen-Mansfield et al. (2016)19	Systematic literature review (k = 38 articles) on correlates and predictors of loneliness in old age.
		Dahlberg et al. (2022)20	Systematic literature review (k = 34 articles) on longitudinal risk factors for loneliness in old age
		Coyle & Dugan (2012)162	Nationally representative study of older adults in the USA (N = 11,825) on the relations between social isolation, loneliness and health.
Relationship quality	Having high-quality relationships is one of the most important protective factors for loneliness.	Cohen-Mansfield et al. (2016)19	Systematic literature review (k = 38 articles) on correlates and predictors of loneliness in old age.
		Dahlberg et al. (2022)20	Systematic literature review (k = 34 articles) on longitudinal risk factors for loneliness in old age.