Om chanting, vagal activity and heart rate variability: current evidence and research perspectives: A narrative review

Abstract

Om (Aum) chanting is a Sanskrit vocalization practice with a long contemplative history that has, over the past two decades, become a focus of quantitative psychophysiological research. A growing body of work links audible Om chanting to measurable shifts in cardiac autonomic regulation, most consistently an increase in high-frequency heart rate variability (HRV) and other indices associated with vagal (parasympathetic) dominance. This review synthesizes current evidence on the relationship between Om chanting, vagal nerve activity, and HRV, and situates the findings within the broader literature on breath-based and vocalization-based vagal stimulation. We examine three converging physiological pathways proposed to explain these effects: respiratory slowing and baroreflex entrainment, vibrotactile stimulation of auricular vagal afferents, and limbic deactivation demonstrated with functional neuroimaging. We then review controlled and uncontrolled studies in healthy adults, yoga practitioners, and clinical populations (notably hypertension), along with related evidence from mantra and prayer recitation, humming, and other slow-breathing practices. Across studies, Om chanting is associated with increased high-frequency power, reduced low-frequency/high-frequency ratio, lower perceived stress and salivary cortisol, and improvements in blood pressure and sleep quality, though effect sizes vary and many studies are small, non-blinded, and methodologically heterogeneous. We conclude by outlining the principal gaps in the literature — including the scarcity of large randomized controlled trials, inconsistent HRV reporting standards, and limited dose-response and long-term data — and propose directions for future research that could clarify the therapeutic potential of Om chanting as a low-cost, non-pharmacological tool for autonomic and cardiovascular health.