The Effects of Mindfulness and Meditation on Vagally-Mediated Heart Rate Variability: A Meta-Analysis.

OBJECTIVE: Heart Rate Variability (HRV) is a marker of autonomic nervous system function associated with both physical and mental health. Many studies have suggested that mindfulness and meditation-based interventions (MBIs) are associated with improvements in HRV, but findings are mixed and to date no comprehensive meta-analysis has synthesized results. METHODS: Systematic literature searches were conducted using PsycINFO, Embase, Medline, CINAHL, ERIC and Scopus to identify randomized controlled trials (RCTs) investigating the effects of predominantly seated MBIs on resting-state vagally-mediated HRV. Risk of bias was judged using the Cochrane Risk of Bias tool. RESULTS: Nineteen RCTs met criteria for inclusion in the meta-analysis. Random-effects meta-analysis found that MBIs were not efficacious in increasing vagally-mediated resting-state HRV relative to control conditions (Hedges' g = 0.38, 95% CI = - 0.014 to 0.77). When removing an outlier (g = 3.22), the effect size was reduced, confidence interval narrowed, and findings remained non-significant (g = 0.19, 95% CI = -0.02 to 0.39). High heterogeneity in results (I2 = 89.12%) could not be explained by a priori determined moderators including intervention duration, study setting and control type. CONCLUSION: There is currently insufficient evidence to indicate that MBIs lead to improvements in vagally-mediated HRV over control conditions. Future large, well-designed RCTs with low risk of methodological bias could help add to the current evidence to elucidate any role MBIs might play in impacting HRV.HRV: heart rate variability; HF-HRV: high-frequency heart rate variability; MBI: mindfulness based intervention; RSA: respiratory sinus arrhythmia.