Association of Loneliness and Social Isolation with Ischemic Heart Disease: A Bidirectional and Network Mendelian...

Observational studies have shown inconsistent associations of loneliness or social isolation (SI) with ischemic heart disease (IHD), with unknown mediators.

Using data from genome-wide association studies of predominantly European ancestry, we performed a bidirectional two-sample Mendelian Randomization (MR) study to estimate causal effects of loneliness ( N = 487,647) and SI traits on IHD ( N = 184,305). SI traits included whether individuals lived alone, participated in various types of social activities, and how often they had contact with friends or family ( N = 459,830 to 461,369). A network MR study was conducted to evaluate the mediating roles of 20 candidate mediators, including metabolic, behavioral and psychological factors.

Loneliness increased IHD risk ( OR= 2.129; 95% confidence interval [ CI]: 1.380 to 3.285), mediated by body fat percentage, waist-hip ratio, total cholesterol, and low-density lipoprotein cholesterol. For SI traits, only fewer social activities increased IHD risk ( OR= 1.815; 95% CI: 1.189 to 2.772), mediated by hypertension, high-density lipoprotein cholesterol, triglycerides, fasting insulin, and smoking cessation. No reverse causality of IHD with loneliness and SI was found.

These findings suggested more attention should be paid to individuals who feel lonely and have fewer social activities to prevent IHD, with several mediators as prioritized targets for intervention.