The Short Version
Multiple peer-reviewed studies and reputable clinical sources associate humming with increased heart rate variability and parasympathetic activation — markers consistent with vagus nerve engagement. At least one PMC study explicitly frames humming as a non-pharmacological vagus nerve stimulation method. However, most evidence relies on indirect autonomic proxies rather than direct vagal measurement, and a 2024 randomized controlled trial found no significant difference in vagal tone between humming and control groups. The claim is broadly supported but overstates the certainty of the underlying mechanism.