Investigating causal relationships between loneliness, social isolation and health

Loneliness and social isolation are important public health concerns due to their associations with a range of health outcomes. However, it is difficult to ascertain whether loneliness and social isolation cause those outcomes or whether the observed associations are biased by confounding and reverse causation. In this study we used a triangulation approach combining observational analysis, sibling control design, and Mendelian Randomisation (a genetically informed causal inference approach), to draw robust conclusions about these relationships. Using a combination of publicly available genome-wide association study (N= 17,526 to 2,083,151) and UK Biobank data (N= 8,075 to 414,432), we examined relationships between loneliness and social isolation and outcomes related to physical health, mental health and wellbeing and general health (reflecting both physical and mental health e.g., multimorbidity). Our results provide evidence for causal effects of loneliness and social isolation on poorer mental health and wellbeing and of loneliness on poorer general health. Evidence was generally stronger for loneliness compared to social isolation. We do not find evidence of effects on specific physical health outcomes; however, we cannot definitively rule out causal relationships. Interventions targeting loneliness and social isolation may be effective strategies for improving general health, mental health and wellbeing outcomes.