Loneliness is associated with diminished heart rate variability reactivity to acute social stress in younger adults.

Loneliness is linked to cardiovascular health, with atypical stress reactivity serving as an underlying mediator. This study aimed to investigate the association between loneliness and heart rate variability (HRV) reactivity to acute social stress in younger adults. A total of 92 participants (52 women; mean age = 22.05 ± 2.25 years; range: 17-29 years) completed the Trier Social Stress Test (TSST), during which their electrocardiogram (ECG) signals were recorded. HRV was assessed using several measures, including the root mean square of successive differences in inter-beat intervals (RMSSD), the percentage of successive inter-beat intervals differing by more than 50 ms (pNN50), and the high-frequency component of HRV (HF-HRV). Loneliness was measured using the revised UCLA Loneliness Scale. Multiple linear regression models were fitted to examine the associations between loneliness and HRV reactivity, controlling for other covariates including age, sex, BMI, neuroticism, social network size, respiration rate and baseline HRV. In the total sample, loneliness was associated with decreased HRV reactivity, indicating a reduced ability of the autonomic nervous system to regulate cardiovascular function under stress. Sex differences were found in the association between loneliness and HRV reactivity, with women exhibiting more significant correlations. These findings suggest that diminished HRV reactivity to social stress may be a physiological mechanism through which loneliness impacts cardiovascular health.