Loneliness and social isolation – disentangling the associations with adverse health outcomes and investigating possible solutions

Background Loneliness and social isolation have been recognised as serious public health issues. Hence, loneliness and social isolation are associated with increased morbidity and mortality. Aim The overall purpose of the present thesis was to examine the association of loneliness and social isolation with adverse health outcomes and determine whether and in what way loneliness and social isolation contribute to poor health. In addition, the present thesis aimed to investigate possible solutions by examining the effect of interventions to reduce loneliness. 

Methods Present thesis comprises four individual pieces of empirical research. Study I and II comprised secondary data from the DNHS (2013) linked with individual-level register data using a prospective cohort design. The studies investigated the associations of loneliness and social isolation with chronic disease outcomes and HCU, respectively. Study III comprised cross-sectional data from the DNHS (2017). The study investigated the association of loneliness and social isolation among adolescents and young adults with physical and mental health. Lastly, the thesis includes a systematic review and meta-analysis investigating the effectiveness of loneliness interventions. 

Results Findings from study I demonstrated that loneliness and social isolation increased the risk of CVD and T2D. However, neither loneliness nor social isolation was associated with the risk of COPD and cancer. Study II demonstrated that loneliness significantly increased the amount of HCU, including GP utilisation and emergency healthcare. However, social isolation did not affect HCU over time. Findings from study III demonstrated that loneliness was strongly associated with poor physical health, including chronic diseases, among adolescents and young adults. Social isolation among adolescents and young adults was not associated with physical health. Both loneliness and social isolation among adolescents and young adults were associated with mental health problems. Findings from study IV demonstrated a small to moderate statistically significant effect of loneliness interventions. Psychological treatment, social support interventions, and social and emotional skills training appeared to be the most effective intervention strategies.

Conclusion Findings from the present thesis show that loneliness and social isolation are associated with chronic disease outcomes in the general population. Moreover, loneliness is associated with increased HCU and correlates strongly with poor physical and mental health among adolescents and young adults. Given the consequences of loneliness and social isolation, there is a need to continue developing and evaluating loneliness interventions.