Social network size moderates the association between loneliness and cardiovascular reactivity to acute stress.

Loneliness and objective measures of social isolation (e.g., social network size) have been associated with increased risk of cardiovascular disease (CVD). However, the evidence is mixed and the precise causal mechanisms remain unclear. Cardiovascular reactivity (CVR) to acute stress has been posited as a proposed mechanism. This study aimed to investigate: (i) effects of loneliness and social isolation on CVR to stress and, (ii) whether the loneliness - CVR relationship was moderated by social network size. Two hundred and six participants from the Pittsburgh Cold Study underwent a modified version of the Trier Social Stress Task. Cardiovascular measures of systolic (SBP) and diastolic blood pressure (DBP) and heart rate (HR) were taken throughout the laboratory stress trial. Hierarchical regression analyses found that social network size was positively associated with DBP reactivity (β = 0.19 95 % CI [0.05, 0.29] p = 0.005), while loneliness was not. In addition, social network size moderated the loneliness - DBP reactivity relationship such that a higher number of outer social network ties were beneficial at lower levels of loneliness but not higher. The current study contributes new evidence linking loneliness and social network size to cardiovascular psychophysiology but raises questions about the loneliness - CVD relationship. The findings confirm the importance of social network size and highlight that the characteristics of the networks may be more important than the number of networks.