Oxidative stress levels are raised in chronic fatigue syndrome and are associated with clinical symptoms.
Kennedy, Gwen, Spence, Vance A, McLaren, Margaret et al. · Free radical biology & medicine · 2005 · DOI
Quick Summary
This study measured harmful molecules called free radicals in the blood of ME/CFS patients and compared them to healthy people. Researchers found that ME/CFS patients had higher levels of these damaging molecules, and in patients without heart disease risk factors, the amount of free radicals correlated with how severe their symptoms were, particularly fatigue after exertion and joint pain.
Why It Matters
This was the first study to demonstrate elevated isoprostanes—a gold-standard marker of oxidative damage—in ME/CFS patients and link them to clinical symptom severity. Identifying a potential biochemical mechanism underlying ME/CFS could inform future therapeutic strategies targeting oxidative stress and validate patient-reported symptoms with objective biomarkers.
Observed Findings
ME/CFS patients had significantly elevated isoprostane levels compared to healthy controls (group 1 p=0.007, group 2 p=0.03).
ME/CFS patients had significantly reduced high-density lipoprotein (HDL) cholesterol in both subgroups (group 1 p=0.011, group 2 p=0.005).
In low cardiovascular-risk ME/CFS patients (group 2), isoprostane levels correlated with total symptom score (p=0.005), joint pain (p=0.002), and postexertional malaise (p=0.027).
Group 2 patients also showed elevated oxidized LDL (p=0.02), indicating free radical damage to lipid molecules.
No significant symptom correlation with oxidative stress markers was found in ME/CFS patients with pre-existing cardiovascular risk factors (obesity or hypertension).
Inferred Conclusions
Excessive free radical generation and oxidative lipid damage occur in ME/CFS patients across both cardiovascular risk profiles.
Oxidative stress may contribute to symptom severity specifically in ME/CFS patients without pre-existing metabolic dysfunction.
Oxidative stress represents a measurable biological abnormality that correlates with subjective symptom burden in a subset of ME/CFS patients.
Remaining Questions
Is oxidative stress a primary cause of ME/CFS or a secondary consequence of the disease process?
What This Study Does Not Prove
This study does not prove that oxidative stress causes ME/CFS symptoms, only that they are associated. The cross-sectional design cannot establish directionality; elevated oxidative stress could be a consequence of ME/CFS rather than a cause. The finding that oxidative stress correlated with symptoms only in the low-risk cardiovascular group requires replication and may reflect confounding or subgroup-specific mechanisms.
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 →
Why does the association between oxidative stress and symptoms appear only in the low-risk cardiovascular group, and what mechanisms underlie this stratification?
Do interventions targeting oxidative stress (antioxidant therapy) improve ME/CFS symptoms, and in which patient subgroups?
Are there additional biomarkers or pathways that explain oxidative stress in the high-risk cardiovascular group where oxidative stress was elevated but uncorrelated with symptoms?