Social Isolation and All-Cause and Heart Disease Mortality Among Working-Age Adults in the United States: The 1998-2014 NHIS-NDI Record Linkage Study

Purpose: Living alone, an indicator of social isolation, has been increasing in the United States; 28% of households in 2019 were one-person households, compared with 13% in 1960. The working-age population is particularly vulnerable to adverse social conditions such as low social support. Although previous research has shown that social isolation and loneliness lead to poorer health and decreased longevity, few studies have focused on the working-age population and heart disease mortality in the United States using longitudinal data. Methods: This study examines social isolation as a risk factor for all-cause and heart disease mortality among U.S. adults aged 18-64 years using the pooled 1998-2014 data from the National Health Interview Survey (NHIS) linked to National Death Index (NDI) (n=388,973). Cox proportional hazards regression was used to model survival time as a function of social isolation, measured by "living alone," and sociodemographic, behavioral, and health characteristics. Results: In Cox regression models with 17 years of mortality follow-up, the age-adjusted all-cause mortality risk was 45% higher (hazard ratio [HR]=1.45; 95% confidence interval [CI]=1.40-1.50) and the heart disease mortality risk was 83% higher (HR=1.83; 95% CI=1.67-2.00) among adults aged 18-64 years living alone at the baseline, compared with adults living with others. In the full model, the relative risk associated with social isolation was 16% higher (HR=1.16; 95% CI=1.11-1.20) for all-cause mortality and 33% higher (HR=1.33; 95% CI=1.21-1.47) for heart disease mortality after controlling for sociodemographic, behavioral-risk, and health status characteristics. Conclusion: In this national study, adults experiencing social isolation had statistically significantly higher relative risks of all-cause and heart disease mortality in the United States than adults living with others.