What comes first: Heart rate variability changes or insomnia? A causal investigation using Mendelian randomization.

Researchers have discovered that changes in heart rate variability (HRV)—a measure of how your nervous system controls heart rhythm—may actually cause insomnia, rather than the other way around. Using genetic data from over 450,000 people, scientists examined whether altered HRV patterns lead to sleep problems or if insomnia causes HRV changes. They found that people with certain HRV patterns had a significantly higher risk of developing insomnia, with some measures showing up to a 91% increased risk. Importantly, when they looked in the reverse direction, they found that having insomnia did not cause HRV changes, suggesting a one-way relationship. This is important because it means that improving your HRV might help prevent or reduce insomnia symptoms. Acupuncture has been shown in previous research to positively influence both heart rate variability and autonomic nervous system function, which this study suggests could be a key mechanism for how acupuncture helps with sleep disorders. Rather than just treating insomnia symptoms, acupuncture may work by addressing the underlying autonomic imbalance reflected in HRV patterns. This provides scientific support for why acupuncture might be effective for sleep problems—it may help regulate the nervous system disruptions that contribute to insomnia in the first place. If you're struggling with insomnia and interested in acupuncture, seek a licensed acupuncturist with experience in treating sleep disorders.

This Mendelian randomization study (n=451,246) examined bidirectional causality between HRV and insomnia using GWAS data. Forward MR analysis revealed significant causal effects of HRV on insomnia: pvRSA/HF (OR=1.437, 95% CI: 1.147-1.801, p=0.002) and SDNN (OR=1.910, 95% CI: 1.092-3.342, p=0.022). Reverse MR found no significant causal effects of insomnia on HRV traits, indicating unidirectional causality. Results remained robust across multiple MR methods (IVW, MR-Egger, weighted median) and sensitivity analyses showed no evidence of horizontal pleiotropy. Clinical implications: Altered HRV appears to be a causal upstream factor in insomnia development rather than a consequence. This supports targeting autonomic nervous system regulation through interventions like acupuncture, which has demonstrated HRV-modulating effects. HRV monitoring may serve as both a biomarker for insomnia risk and a therapeutic outcome measure in clinical practice.