Social Disconnection, Loneliness, and All-Cause Mortality: Updated Dose-Response Meta-Analysis of 84 Longitudinal Cohort Studies With 8.4 Million Participants

This study investigates dose-response meta-analysis of social isolation and loneliness with all-cause mortality, cardiovascular disease incidence, and dementia onset across 84 longitudinal cohort studies with 8.4 million participants within the context of social epidemiology and public health, an area of growing scientific importance given its implications for national loneliness strategy design (UK, U.S.), social prescribing intervention evidence, and primary care loneliness screening protocol development. Using systematic review (MEDLINE, Embase, PsycINFO, Cochrane through December 2024) with random-effects meta-analysis, REML estimation, dose-response modeling (restricted cubic splines), meta-regression for moderators, and Egger test for publication bias, we examine social isolation activating hypothalamic-pituitary-adrenal axis stress response, increasing cortisol and inflammatory cytokines (IL-6, CRP) that accelerate cardiovascular disease, immune senescence, and neurodegeneration; loneliness as perceived isolation independently activating amygdala threat hypervigilance that disrupts sleep, physical activity, and health behaviors in 84 longitudinal studies (48 social isolation, 36 loneliness) with 8.4 million participants; 4.2 million deaths/events across studies; mean follow-up 8.4 years; studies from 28 countries drawn from systematic review of cohort studies published 1980-2024 from MEDLINE/Embase/PsycINFO; included studies from North America (38%), Europe (42%), Asia-Pacific (14%), other (6%). Results indicate that high social isolation associated with all-cause mortality HR=1.32 (1.24-1.40), cardiovascular HR=1.28, dementia HR=1.48; loneliness all-cause mortality HR=1.26 (1.18-1.34); dose-response shows near-linear increase in mortality risk with increasing isolation; effect 1.8x larger in adults <65 vs. older (p < 0.001), with isolation mortality HR=1.32; dementia HR=1.48; loneliness HR=1.26; 1.8x larger in <65 as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to social epidemiology and public health and carry actionable implications for the design of programs and policies targeting national loneliness strategy design (UK, U.S.), social prescribing intervention evidence, and primary care loneliness screening protocol development.