Loneliness and all cause mortality in Australian women aged 45 years and older: causal inference analysis of longitudinal data

Objective To examine the causal effects of loneliness on mortality among Australian women aged 45 years and older. Design Causal inference analysis of longitudinal data. Participants A population based sample of Australian women aged 45 years and older (n=11 412). Main outcome measures Targeted maximum likelihood estimations were used to analyse the causal relationship between loneliness and all cause mortality over 18 years. The adjusted risk of death associated with the total number of loneliness waves (loneliness persistency) and the consecutive number of loneliness waves (loneliness chronicity) was presented using risk ratios and risk differences with 99.5% confidence intervals (CIs). Results The association between the number of waves of reported loneliness and mortality risk showed a dose-dependent pattern. Compared with women who did not report loneliness in any wave, people who reported loneliness at two, four, and six waves had an incrementally higher risk of dying during the follow-up period: risk ratio 1.49 (99.5% CI 1.26 to 1.75) at two waves, 2.18 (1.79 to 2.66) at four waves, and 3.15 (2.35 to 4.23) at six waves. The risk difference showed a similar trend to the risk ratios with higher excess mortality among women who reported experiencing loneliness for six waves compared with those who did not report loneliness at all (10.86% (99.5% CI 10.58% to 11.15%)). Similar trends were found when loneliness was experienced across consecutive waves. Conclusions Loneliness seems to be causally linked to mortality risk with a dose-dependent relationship. Acknowledging loneliness as an independent health risk underscores the importance of screening for loneliness and incorporating public health interventions into healthcare practices.