Social isolation and loneliness and their association with all-cause mortality. A population-based longitudinal study in Norway: The Tromsø Study 1994-2023.

Objectives: Loneliness and social isolation are associated with increased mortality, but few studies have assessed this association over long time in young adults. Methods: The study sample comprised 9061 women and 8735 men aged 25 to 69 years who participated in the Tromsø4 survey (1994-95, baseline) of the Tromsø Study, Norway. A subset of the study sample also attended the Tromsø5 (2001), Tromsø6 (2007-08), and Tromsø7 (2015-16) surveys. Participants were followed up for all-cause mortality until November 2023; with 1630 women and 2099 men deceased. Information on social isolation (least isolated, modestly isolated, and most isolated) and loneliness (yes, no) were taken from self-administered questionnaires. Sex-specific, time-varying Cox models were employed, updating exposures and covariates from Tromsø5. Results: Most-isolated versus least-isolated women and men had hazard ratios of 1.37 (95 % confidence interval 1.18-1.59) and 1.41 (1.25-1.60), respectively, after adjustment for covariates. These hazard ratios were higher in younger adults (HR = 1.55 in women and HR = 1.76 in men aged <50 years at baseline), though the age-isolation interaction was not statistically significant in women ( Conclusion: Both social isolation and loneliness are strongly associated with all-cause mortality, particularly among younger adults, underscoring their importance as public health concerns.