Diurnal variation of adrenocortical activity in chronic fatigue syndrome.
MacHale, S M, Cavanagh, J T, Bennie, J et al. · Neuropsychobiology · 1998 · DOI
Quick Summary
This study measured stress hormone (cortisol) levels in 30 ME/CFS patients and 15 healthy controls at different times of day. The researchers found that while individual cortisol measurements were similar between groups, ME/CFS patients showed a flattened pattern—their cortisol levels didn't drop as much in the evening as they should. Higher evening cortisol levels were connected to worse overall health and physical functioning in ME/CFS patients.
Why It Matters
Understanding hormone dysfunction in ME/CFS may help explain fatigue and functional impairment. This study identifies a specific, measurable abnormality in the body's stress response system that correlates with disability severity, potentially opening avenues for diagnostic biomarkers and targeted treatments.
Observed Findings
Morning cortisol levels were non-significantly lower in CFS patients compared to controls
Evening cortisol levels were non-significantly higher in CFS patients compared to controls
Diurnal (morning-to-evening) change in cortisol was significantly blunted in CFS patients (p < 0.05)
Evening cortisol levels correlated significantly with measures of general health and physical functioning in CFS patients
Diurnal cortisol change correlated positively with functional improvement over the past year and current social functioning
Inferred Conclusions
Adrenocortical dysfunction characterized by flattened diurnal cortisol variation is present in ME/CFS
Abnormal cortisol patterns are associated with worse disability and functional impairment in ME/CFS
A relationship exists between hypothalamic-pituitary-adrenal (HPA) axis function and ME/CFS disability, though the causal mechanism remains unclear
Remaining Questions
Does abnormal cortisol variation cause ME/CFS symptoms, result from chronic illness, or reflect a shared underlying dysfunction?
What is the mechanism linking flattened diurnal cortisol variation to physical disability and poor functioning?
What This Study Does Not Prove
This study does not prove that abnormal cortisol patterns cause ME/CFS symptoms or disability—correlation does not equal causation. The cross-sectional design cannot determine whether hormone changes precede illness onset or result from prolonged illness. The sample size (30 patients) is relatively small, and findings may not generalize to all ME/CFS populations.
Tags
Symptom:Fatigue
Biomarker:Blood Biomarker
Method Flag:Weak Case DefinitionSmall SampleExploratory Only