How many studies support HRV?

A 2017 meta-analysis found HRV biofeedback training — deliberately practicing slow, paced breathing to increase heart rate variability — produces a meaningful reduction in self-reported stress and anxiety, a mechanism-consistent finding supported by a separate meta-analysis showing voluntary slow breathing reliably increases HRV. That's backed by 9 published studies in Vitaebase's database, including 5 randomized controlled trials and 4 meta-analyses, the most recent from 2026 -- a fairly substantial body of research for a single topic.