Loneliness as a Pathway from Social Isolation to Psychological Distress: A Cross-Sectional Mediation Study in Portuguese Adults

Social disconnection has become a public-health concern, but it remains unclear whether mental-health symptoms are more closely related to limited social contact or to the subjective experience of loneliness. This cross-sectional study examined 632 self-selected adults living in Portugal, recruited online, and explored whether loneliness helps explain the association between social isolation and psychological distress across small, medium, and large cities. Participants completed self-report measures of loneliness, social isolation, depression, anxiety, stress, and positive and negative affect. Loneliness was a salient experience: the mean score was close to the scale midpoint, and 36.2% of participants scored above it. Higher loneliness was associated with greater psychological distress, greater social isolation, lower positive affect, and higher negative affect. When loneliness was considered together with social isolation, the direct link between isolation and distress became minimal, suggesting that distress was more closely connected to how social disconnection was experienced than to contact frequency alone. This pattern was similar across city sizes, and average levels of loneliness, isolation, distress, and affect did not meaningfully differ between small, medium, and large cities. Overall, the findings are consistent with loneliness as a candidate target for mental-health promotion in this sample of Portuguese adults, although longitudinal studies are needed to clarify causal pathways.