Association between loneliness, social isolation and incident depression: a prospective study based on UK Biobank

In existing research on social isolation and loneliness, although both are widely recognized as independent risk factors for health, their interrelationship has not been fully explored. Therefore, clarifying whether there is an interaction between them is crucial to understanding their impact on an individual's health.

Loneliness and social isolation were assessed by means of touch-screen questionnaire. The occurrence of clinically diagnosed depression was determined based on the section of mental and behavioral disorders of the UKB's first occurrence fields. Cox proportional hazard models and additive and multiplicative models were used to assess the associations between loneliness, social isolation, and incident depression.

Among the 339,051 participants, 48.47 % were men and 13,096 depression cases were recorded during a median follow-up period of 12.45 years. Loneliness (yes vs no: adjusted HR: 1.77; 95 % CI: 1.67-1.89) and social isolation (yes vs no: adjusted HR: 1.14; 95 % CI: 1.08-1.21) were associated with an increased risk of incident depression. The association between increased risk of depression and social isolation was modified by gender (P_interaction = 0.018). The interactive effect of loneliness and social isolation was not statistically associated with incident depression (P = 0.124).

Loneliness and social isolation were independently associated with a higher risk of incident depression, with no interaction between the two.