Effect of Acupuncture on Heart Rate Variability: A Systematic Review

This systematic review with meta-analysis investigated the effect of acupuncture on heart rate variability (HRV), an important marker of autonomic nervous system function. HRV reflects the balance between the sympathetic and parasympathetic nervous systems, providing information about the body's capacity to adapt to different situations of stress and relaxation. The study included 14 randomized controlled trials, involving healthy and unhealthy participants treated with traditional acupuncture. The investigators analyzed various HRV parameters, including low frequency (LF), high frequency (HF), and the LF/HF ratio, which are indicators of sympathetic and parasympathetic activity of the autonomic nervous system.

The methodology was rigorous, following specific inclusion criteria that limited the analysis to studies using needle acupuncture, compared with sham acupuncture or no-treatment controls. The main results showed that acupuncture had a significant decreasing effect on the low-frequency (LF) component and on the LF/HF ratio of HRV in unhealthy participants. In healthy participants, a significant decrease in normalized LF was observed. These findings are clinically relevant because they suggest that acupuncture may modulate autonomic nervous system activity, particularly by increasing parasympathetic influence, which is associated with states of relaxation, recovery, and restorative functions of the body.

The study also analyzed specific effects of individual acupuncture points. Point ST-36 (Zusanli 足三里) showed significant effects in reducing high frequency in healthy participants, whereas point PC-6 (Neiguan 內關) demonstrated effects in both healthy and unhealthy participants. These findings are consistent with the traditional use of these points in Chinese medicine — ST-36 is known for its action on general well-being and PC-6 for its calming effects on the cardiovascular system. However, the results also revealed some important limitations.

Heterogeneity across studies was high (35-99%), indicating significant variations in methods, populations, and outcomes among the different studies analyzed. In addition, the effect on the high-frequency (HF) component was not consistently significant, and in some cases, the control/sham group showed better results than the real acupuncture group. Risk-of-bias assessment revealed that many studies had methodological limitations, particularly in randomization, blinding of participants and assessors, and allocation concealment. Only a small percentage of studies met all methodological quality criteria, which may have influenced the results.

The authors concluded that there is partial evidence that acupuncture may modulate the low-frequency component of HRV, especially in unhealthy populations. This suggests a possible mechanism by which acupuncture exerts its therapeutic effects — through modulation of the autonomic nervous system. However, more high-quality studies, with larger samples and better methodological control, are needed to definitively establish whether HRV can be used as a reliable indicator of the therapeutic effects of acupuncture. The clinical implications of these findings are significant for understanding the mechanisms of action of acupuncture and its evidence-based application.