A systematic review of state loneliness in daily life using intensive longitudinal methods

Loneliness, including its associations with mental health, is recognised as a major global public health concern. While much research has focused on chronic loneliness, state loneliness - experienced in moment-to-moment contexts - remains underexplored. This gap is important, as daily experiences may provide critical opportunities for intervention. Intensive data collection approaches such as Ecological Momentary Assessment (EMA), Experience Sampling Method (ESM) and Daily Diary are well-suited for moment-to-moment capture and a review of their use for illuminating loneliness would be valuable for characterizing the state of the art and identifying gaps. This review thus synthesised findings from the intensive data collection approach to explore factors that may influence state loneliness and its consequences for mental health/well-being across all ages, providing valuable insights for targeted interventions.

This review follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Four databases (PsycINFO, PubMed, Web of Science, and EMBASE) were searched from inception to 25th May 2026. Abstracts and full texts were screened, and the quality of the included studies was assessed. Data extraction was conducted independently by two reviewers.

One hundred and seventeen studies were included in this review, addressing measurement practices and quality (RQ1-2), predictors and correlates of state loneliness (RQ3), and mental health and wellbeing outcomes (RQ4). State loneliness was predominantly assessed using single items with varied response formats; most items met expert-based formulation criteria, though empirical psychometric evidence was rarely reported. Associations were observed between state loneliness and mental health outcomes (e.g., internalising, suicidality) and social interaction, with several studies reporting effects in both directions, though the nature of these associations varied with study design and analytic approach. Other factors, including physical health, age, and gender, were also linked to state loneliness.

Taken together, the review provides an improved understanding of the factors that may influence loneliness and its consequences for mental health/well-being. The results of the review could help to inform targeted prevention and intervention strategies for all age ranges, facilitating the mitigation of loneliness.