Loneliness, social isolation, and accumulation of chronic conditions: A nationwide longitudinal study in Japan

Loneliness and social isolation are related but distinct dimensions of social disconnection, but their longitudinal associations with chronic condition accumulation remain unclear in non-Western populations.

We analyzed 8721 adults aged 18 years or older who completed the 2021 and 2025 waves of the Japan "COVID-19 and Society" Internet Survey. Loneliness and social isolation were assessed in 2021, during the COVID-19 pandemic, using the UCLA 3-item Loneliness Scale and the 6-item Lubben Social Network Scale. The outcome was the newly reported presence in 2025 of at least one of 14 physician-diagnosed chronic conditions not reported as currently present in 2021. Standardized inverse probability-weighted logistic regression estimated adjusted odds ratios (ORs) per 1-SD higher loneliness score and per 1-SD lower social network score, adjusting for both exposures, sociodemographic factors, and baseline condition count.

Among 8721 participants, 2399 (27.5%) reported at least one new condition. Loneliness was associated with the outcome (OR, 1.24; 95% CI, 1.13-1.36), whereas social isolation was not (OR, 1.06; 95% CI, 0.97-1.17). Additional adjustment for baseline psychological distress attenuated the loneliness association (OR, 1.10; 95% CI, 0.98-1.23).

Loneliness, but not social isolation, was associated with subsequent reporting of new chronic conditions. Psychological distress may partly account for this association.