Plasma and urinary carnitine and acylcarnitines in chronic fatigue syndrome.
Jones, Mark G, Goodwin, C Stewart, Amjad, Saira et al. · Clinica chimica acta; international journal of clinical chemistry · 2005 · DOI
Quick Summary
Researchers tested whether people with ME/CFS have low levels of carnitine, a substance that helps muscles produce energy. They compared blood and urine samples from 31 ME/CFS patients with samples from healthy people and patients with other conditions. The study found no significant differences in carnitine levels between the groups, suggesting that low carnitine is not responsible for the fatigue experienced by ME/CFS patients.
Why It Matters
Since several earlier studies had suggested carnitine deficiency might explain ME/CFS muscle fatigue, this well-controlled study provides important evidence against this hypothesis. Ruling out carnitine abnormalities helps redirect research efforts toward other biological mechanisms of ME/CFS fatigue.
Observed Findings
No significant differences in plasma total carnitine between CFS and control groups
No significant differences in plasma free carnitine between CFS and control groups
No significant differences in plasma acylcarnitine concentrations between CFS and control groups
No significant differences in urinary carnitine excretion rates between CFS and control groups
No differences observed between CFS patients and depression or rheumatoid arthritis comparison groups
Inferred Conclusions
Carnitine homeostasis abnormalities are unlikely to have a significant role in CFS aetiology
Plasma and urinary carnitine abnormalities do not explain the muscle fatigue observed in CFS patients
Earlier reports of low serum carnitine in CFS patients may have resulted from methodological limitations or patient selection bias
Remaining Questions
Do intramuscular carnitine levels or carnitine metabolism differ in ME/CFS, despite normal plasma/urine concentrations?
Could carnitine transport or utilization at the cellular level be impaired in ME/CFS despite adequate circulating levels?
What This Study Does Not Prove
This study does not prove that carnitine metabolism is completely normal in all ME/CFS patients—it only examined steady-state plasma and urine levels. It also does not assess intramuscular carnitine concentrations or carnitine utilization during exercise, which could theoretically differ from blood levels. The findings apply specifically to the UK patient population studied and may not generalize to all ME/CFS presentations.