Loneliness, social isolation, and living alone: a comprehensive systematic review, meta-analysis, and meta-regression of mortality risks in older adults

Loneliness, social isolation, and living alone are significant risk factors for mortality, particularly in older adults. This systematic review and meta-analysis aimed to quantify their associations with all-cause and cause-specific mortality in older adults, broadening previous research by including more social factors. Comprehensive searches were conducted in PubMed, APA PsycINFO, and CINAHL until December 31, 2023, following PRISMA 2020 and MOOSE guidelines. Studies included were prospective cohort or longitudinal studies examining the relationship between loneliness, social isolation, living alone, and mortality. Quality was assessed using the Newcastle-Ottawa Scale. Meta-analyses used random-effects models with the Restricted Maximum Likelihood method. Subgroup and meta-regression analyses explored the relationships further. Of 11,964 identified studies, 86 met the inclusion criteria. Loneliness was associated with increased all-cause mortality (HR 1.14, 95% CI 1.10-1.18), with substantial heterogeneity (I-2 = 84.0%). Similar associations were found for social isolation (HR 1.35, 95% CI 1.27-1.43) and living alone (HR 1.21, 95% CI 1.13-1.30). Subgroup analyses revealed variations based on factors like sex, age, region, chronic diseases, and study quality. Meta-regression identified longer follow-up, female sex, validated social network indices, adjustments for cognitive function, and study quality as significant predictors of mortality risks. These findings highlight the need for public health interventions to address these social factors and improve health outcomes in older adults. However, further research is needed due to variability and heterogeneity across studies. Also studying the cumulative effect of these factors on mortality risks will be of considerable interest.