1. In this systematic review and meta-analysis, loneliness at baseline was associated with new onset of depression.
2. Additionally, there was a positive association between loneliness and both anxiety and self-harm.
Evidence Rating Level: 1 (Excellent)
Research suggests that those with longstanding mental health disorders are at the highest risk of loneliness. However, the association between loneliness and mental health is poorly characterized and the most recent meta-analysis on loneliness did not include a systematic literature search. As a result, the objective of the present systematic review was to determine if loneliness led to the onset of mental health problems in the general population.
Of 33,317 identified records, 32 studies from database inception to August 2021 were included in the systematic review. Of these, 7 studies were included in the main meta-analysis (8 cohorts). Studies were excluded if loneliness and mental health problems were not the primary exposures and outcomes or if they included participants with intellectual disabilities, organic mental illnesses, or children under the age of 16. Quality assessment was performed using the Mixed Methods Appraisal Tool (MMAT) as well as the Newcastle-Ottawa Scale (NOS). The systematic review was prepared using PRISMA guidelines. The primary outcome was mental health problems, including depression, anxiety, bipolar disorder, personality disorder, psychosis, etc.
Results demonstrated that the odds of developing new depression in adults more than doubled in those who are often lonely compared to those who are not/rarely lonely, even after adjustment of other factors. Furthermore, five of six studies looking at anxiety and loneliness found a positive association between the two. In a small number of studies loneliness was also associated with other common mental health problems, including suicidal ideation and self-harm. However, the study was limited by the low rates of depression in some of the included studies which means the reported effects of loneliness on depression may be underestimated. Nonetheless, these results suggest that loneliness may place individuals at risk of developing various mental health disorders.
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