Al-Hakeim, Hussein Kadhem, Khairi Abed, Anwar, Rouf Moustafa, Shatha et al. · Frontiers in molecular neuroscience · 2023 · DOI
This study looked at 90 Long COVID patients and measured specific molecules in their blood related to how their body processes an amino acid called tryptophan. The researchers found that patients with the most severe Long COVID symptoms had low tryptophan levels and high levels of a related compound called kynurenine, along with markers of inflammation. These three measurements together explained about 40% of why patients had fatigue, pain, depression, and anxiety symptoms.
This research is relevant to ME/CFS because it identifies a potential biological mechanism—tryptophan depletion and inflammatory activation—that could explain why post-viral patients develop persistent fatigue, pain, and mood symptoms. Understanding these shared molecular pathways may help researchers develop targeted treatments and biomarkers for severe Long COVID and potentially inform ME/CFS research directions.
This study does not prove that tryptophan depletion causes Long COVID symptoms; it shows correlation only. The cross-sectional design cannot establish temporal sequence or causality, and the findings describe Long COVID specifically, not necessarily ME/CFS or other chronic fatigue conditions. The biomarkers explained only 40% of symptom variance, leaving 60% unexplained by mechanisms not measured here.
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 →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Al-Hakeim, Hussein Kadhem, Khairi Abed, Anwar, Rouf Moustafa, Shatha, Almulla, Abbas F, & Maes, Michael (2023). Tryptophan catabolites, inflammation, and insulin resistance as determinants of chronic fatigue syndrome and affective symptoms in long COVID.. Frontiers in molecular neuroscience. https://doi.org/10.3389/fnmol.2023.1194769
BibTeX
@article{mecfsatlas-al-hakeim-2023-tryptophan-catabolites,
author = {Al-Hakeim, Hussein Kadhem and Khairi Abed, Anwar and Rouf Moustafa, Shatha and Almulla, Abbas F and Maes, Michael},
title = {Tryptophan catabolites, inflammation, and insulin resistance as determinants of chronic fatigue syndrome and affective symptoms in long COVID.},
journal = {Frontiers in molecular neuroscience},
year = {2023},
doi = {10.3389/fnmol.2023.1194769},
note = {PubMed: 37333619},
url = {https://www.mecfsatlas.com/evidence/al-hakeim-2023-tryptophan-catabolites},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/al-hakeim-2023-tryptophan-catabolites
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