Background Interest in loneliness and social isolation as risk factors for premature mortality has recently gained increased attention in both the research literature and public discourses. This has resulted in the established of loneliness taskforces in both Ireland and the United Kingdom. Both loneliness and social isolation have previously been linked to a host of adverse health outcomes, including cardiovascular disease, depression, reduced immune and cognitive functioning, and mortality. Loneliness is most often conceptualised as the subjective assessment of an individual’s social relationships while social isolation is the objective quantitative measure of social contacts. Loneliness and social isolation that have been shown to be distinct yet synergistic constructs.

This study examined the association between loneliness, social isolation, and all-cause and cardiovascular mortality in Ireland and also tested the hypothesis that loneliness provides a mechanistic pathway that explains the association between social network size and mortality. This is the first study in Ireland to use linked survey-health assessment-mortality data, combining rich individual-level data from the Irish Longitudinal Study on Ageing (TILDA) with official death certificate data provided by the official mortality register.

Methods The sample included 6,800 participants, including 654 decedents (with 199 deaths due to cardiovascular disease) who had participated in the first round of TILDA. Underlying and contributory causes of death were coded using the International Classification of Diseases, Injuries and Causes of Death (ICD-10). Loneliness was measured using the five-item University of California at Los Angeles (UCLA) Loneliness Scale. Social isolation was measured using the Berkman–Syme Social Network Index. Cox proportional hazards ratios were estimated to assess the association between loneliness, social isolation and mortality while controlling for demographic and socio-economic characteristics, health status, and related behaviours. SEM path analysis was used to identify mechanistic pathways.

Results The average age of death was 78 years. After controlling for other factors, the most lonely (HR 1.39 95% CI: 1.08–1.78, p<0.01) and most isolated (HR 1.62 95% CI: 1.21–2.17, p<0.001) had an increased all-cause mortality risk. A similar association was observed between loneliness and cardiovascular deaths (HR 1.68 95% CI: 1.06–2.66, p<0.05). The association between social isolation and mortality was partially mediated by loneliness.

Conclusion These findings add to the growing body of evidence that loneliness and social isolation are associated with premature mortality. They also shed new light on potential mechanistic pathways that partially explain these associations.