OBJECTIVES To effectively reduce loneliness in older adults, interventions should be based on firm evidence regarding risk factors for loneliness in that population. This systematic review aimed to identify, appraise and synthesise longitudinal studies of risk factors for loneliness in older adults.

METHODS Searches were performed in June 2018 in PsycINFO, Scopus, Sociology Collection and Web of Science. Inclusion criteria were: population of older adults (M = 60+ years at outcome); longitudinal design; study conducted in an OECD country; article published in English in a peer-review journal. Article relevance and quality assessments were made by at least two independent reviewers.

RESULTS The search found 967 unique articles, of which 34 met relevance and quality criteria. The Netherlands and the United States together contributed 19 articles; 17 analysed national samples while 7 studies provided the data for 19 articles. One of two validated scales was used to measure loneliness in 24 articles, although 10 used a single item. A total of 120 unique risk factors for loneliness were examined. Risk factors with relatively consistent associations with loneliness were: not being married/partnered and partner loss; a limited social network; a low level of social activity; poor self-perceived health; and depression/depressed mood and an increase in depression.

CONCLUSION Despite the range of factors examined in the reviewed articles, strong evidence for a longitudinal association with loneliness was found for relatively few, while there were surprising omissions from the factors investigated. Future research should explore longitudinal risk factors for emotional and social loneliness.