Nonlinear Relations Between Resting Heart Rate Measures and Health Risk Behavior in Emerging Adulthood

INTRODUCTION: Resting heart rate (HR) measures reflect autonomic processes that could predict health risk behavior (HRB) in emerging adulthood when risky behavior is prominent. However, prior studies and extant theories are inconsistent, such that the relationships between HR measures and HRB could be positive or negative in direction. To reconcile these inconsistencies, we predicted that positive and negative relations between HR measures and HRB propensity exist together in a quadratic function. METHODS: The current study tested this nonlinear hypothesis in a sample of young adults (N = 89, Mean Age = 21 years, 66% Female) who completed three separate resting baseline periods. ECG was recorded throughout to compute mean HR and high-frequency heart rate variability (HF-HRV) as partial and pure indices of resting vagal activity, respectively. HRB propensity was self-reported on the health/safety and recreational subscales of the Domain-Specific Risk-Taking questionnaire. RESULTS: Resting HR and HF-HRV each exhibited quadratic associations with HRB propensity that were statistically separate from one another. In all functions, moderate levels of mean HR or HF-HRV were related to a reduced propensity for risk-taking behavior. CONCLUSIONS: Findings suggest two potential pathways by which heart rate measures might contribute to HRB in emerging adulthood: one through heightened vagal activity, which may signal under-arousal, and the other through reduced vagal activity, which may reflect deficient self-regulation.