Loneliness and mood disorders: consequence, cause and/or unholy alliance?

Studies carried out before and during the COVID-19 pandemic found that feelings of loneliness can be both consequences and precursors of persistent depression and bipolar disorder. Mood symptoms and loneliness have a cumulative negative effect on physical and mental health outcomes. Conceptual overlaps and relations between loneliness and mood symptoms should be clarified in qualitative studies. Theory-driven intervention models should be developed and tested in methodologically robust studies.