Ruiz-Núñez, Begoña, Tarasse, Rabab, Vogelaar, Emar F et al. · Frontiers in endocrinology · 2018 · DOI
This study compared thyroid hormone levels in 98 ME/CFS patients with 99 healthy controls and found that ME/CFS patients were more than twice as likely to have low levels of an active thyroid hormone called T3. The patients also showed signs of chronic low-grade inflammation and had more reverse T3 (an inactive form), which may explain why their bodies aren't producing or using thyroid hormones efficiently.
If confirmed, these findings could explain the pervasive fatigue and metabolic dysfunction experienced by many ME/CFS patients and might identify a treatable subgroup. This opens the possibility of targeted thyroid hormone or iodine supplementation trials, which could represent a novel therapeutic approach for a condition with few established treatments.
This study does not prove that low T3 syndrome causes ME/CFS or that thyroid hormone replacement would improve symptoms—it demonstrates an association only. The cross-sectional design cannot establish causation or determine whether the low T3 is a primary problem or a secondary consequence of chronic inflammation. The findings require replication and extension before clinical recommendations can be made.
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
Ruiz-Núñez, Begoña, Tarasse, Rabab, Vogelaar, Emar F, Janneke Dijck-Brouwer, D A, & Muskiet, Frits A J (2018). Higher Prevalence of "Low T3 Syndrome" in Patients With Chronic Fatigue Syndrome: A Case-Control Study.. Frontiers in endocrinology. https://doi.org/10.3389/fendo.2018.00097
BibTeX
@article{mecfsatlas-ruiz-nez-2018-higher-prevalence,
author = {Ruiz-Núñez, Begoña and Tarasse, Rabab and Vogelaar, Emar F and Janneke Dijck-Brouwer, D A and Muskiet, Frits A J},
title = {Higher Prevalence of "Low T3 Syndrome" in Patients With Chronic Fatigue Syndrome: A Case-Control Study.},
journal = {Frontiers in endocrinology},
year = {2018},
doi = {10.3389/fendo.2018.00097},
note = {PubMed: 29615976},
url = {https://www.mecfsatlas.com/evidence/ruiz-nez-2018-higher-prevalence},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-29. https://www.mecfsatlas.com/evidence/ruiz-nez-2018-higher-prevalence
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