E0 ConsensusModerate confidencePEM not requiredMeta-AnalysisPeer-reviewedMachine draft
Reduced Heart Rate Variability in Patients With Medically Unexplained Physical Symptoms: A Meta-Analysis of HF-HRV and RMSSD.
Vreijling, Sarah R, Troudart, Yael, Brosschot, Jos F · Psychosomatic medicine · 2021 · DOI
Quick Summary
This study looked at heart rate variability (how much your heart rate changes moment-to-moment) in people with chronic fatigue syndrome, irritable bowel syndrome, and fibromyalgia. Researchers combined results from 58 previous studies and found that patients with these conditions had lower heart rate variability than healthy people, suggesting their nervous systems may not be regulating heart rate as flexibly as they should.
Why It Matters
This meta-analysis provides robust evidence that autonomic nervous system dysregulation—specifically reduced parasympathetic activity—is a consistent biological feature across ME/CFS and related syndromes. Understanding this shared mechanism may help explain symptom overlap and guide development of treatments targeting autonomic function.
Observed Findings
- Patients with MUPS had significantly lower RMSSD than healthy controls (22 studies, effect size -0.37)
- Patients with MUPS had significantly lower HF-HRV than healthy controls (52 studies, effect size -0.69)
- Findings were consistent across three different syndromes (CFS, IBS, and fibromyalgia)
- Sample age and publication year explained variation in RMSSD results
- Methodological confounders explained variation in HF-HRV results
Inferred Conclusions
- Autonomic nervous system dysregulation, particularly reduced parasympathetic activity, appears to be a consistent biological feature of MUPS and related syndromes
- This dysregulation may represent a shared underlying mechanism across distinct syndromes
- Autonomic dysfunction may have implications for understanding the pathophysiology and developing treatments for these conditions
Remaining Questions
- What causes the autonomic dysregulation in these syndromes, and is it primary or secondary to other pathophysiological processes?
- Does the degree of autonomic dysregulation correlate with symptom severity or predict treatment response?
What This Study Does Not Prove
This study does not establish that autonomic dysregulation *causes* these syndromes; it only shows an association. The findings cannot explain why some individuals develop autonomic dysregulation or whether correcting it would resolve symptoms. Individual variation within each syndrome is substantial, and the mechanisms underlying this dysregulation remain unclear.
Tags
Symptom:Fatigue
Biomarker:Blood Biomarker
Method Flag:PEM Not DefinedMixed Cohort
Metadata
- DOI
- 10.1097/PSY.0000000000000874
- PMID
- 33065584
- Review status
- Machine draft
- Evidence level
- Established evidence from major reviews, guidelines, or evidence maps
- Last updated
- 8 April 2026
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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