E2 ModeratePreliminaryPEM unclearCase-ControlPeer-reviewedMachine draft
Sex differences in plasma prolactin response to tryptophan in chronic fatigue syndrome patients with and without comorbid fibromyalgia.
Weaver, Shelley A, Janal, Malvin N, Aktan, Nadine et al. · Journal of women's health (2002) · 2010 · DOI
Quick Summary
Researchers gave patients with ME/CFS a tryptophan infusion (a building block for serotonin, a brain chemical) to see how their bodies would respond. They found that women with ME/CFS alone had a stronger response in a hormone called prolactin compared to healthy women, but women with ME/CFS plus fibromyalgia did not show this difference. Men in all groups showed similar responses, suggesting ME/CFS may work differently in women than in men.
Why It Matters
This study suggests that ME/CFS in women may involve different biological mechanisms than fibromyalgia, and that sex differences in ME/CFS prevalence may reflect distinct neurobiological pathways. Understanding whether ME/CFS and fibromyalgia are separate conditions has important implications for diagnosis, treatment research, and clinical management.
Observed Findings
- Women with ME/CFS alone showed upregulated plasma prolactin responses compared to healthy controls.
- Women with CFS+FM did not show elevated prolactin responses compared to controls.
- No significant group differences in plasma prolactin response were observed among men (CFS alone, CFS+FM, or controls).
- Plasma tryptophan and kynurenine concentrations did not differ significantly among any of the groups.
Inferred Conclusions
- Serotonergic dysregulation in women with ME/CFS alone differs from women with comorbid ME/CFS+FM, suggesting these may be distinct biological entities.
- The sex-specific pattern of serotonergic abnormality may partially explain why ME/CFS is more prevalent in women than men.
- ME/CFS in women appears to be a different illness from fibromyalgia based on differential serotonergic function.
Remaining Questions
- Why do men with ME/CFS not show the same prolactin response elevation seen in women, and what are the mechanistic underpinnings of this sex difference?
- Does the elevated prolactin response in women with CFS alone represent a cause, consequence, or biomarker of disease, and does it correlate with symptom severity or progression?
- How do other aspects of serotonergic function (beyond prolactin response) differ between ME/CFS alone and CFS+FM phenotypes?
What This Study Does Not Prove
This study does not prove that elevated prolactin response causes ME/CFS symptoms, only that it is associated with the condition in women. The findings are correlational and based on a single tryptophan challenge test; they do not establish whether this difference is a primary cause, consequence, or marker of disease. The study also does not address whether these findings apply to men with ME/CFS or explain the mechanistic basis of the sex difference.
Tags
Symptom:Fatigue
Biomarker:Blood Biomarker
Method Flag:Small SampleExploratory OnlyMixed CohortSex-Stratified
Metadata
- DOI
- 10.1089/jwh.2009.1697
- PMID
- 20384451
- Review status
- Machine draft
- Evidence level
- Single-study or moderate support from human research
- 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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