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

Purpose of review People with persistent depressive disorders and with bipolar disorder are more likely to feel lonely than people in the general population. This evidence update focused on studies in the last 2 years, characterized by the COVID-19 pandemic and consequent social distancing directives. Recent findings Longitudinal studies identified that people who feel lonely are more likely to become depressed or to experience relapse of mood disorders. There is emerging evidence that feelings of loneliness or mandatory social isolation can precede manic episodes. Hence the relationship between loneliness and mood disorders is complex and bidirectional. Interventions were developed to reduce loneliness in people with mental health problems, including depressive disorders, through cognitive modification and/or supported socialisation. No loneliness-focused interventions have been specifically tailored to people with bipolar disorder. Summary 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.