A company called Holtorf Medical Group writes in Are All Chronic Fatigue Syndrome and
Fibromyalgia Patients Low Thyroid

There is mounting evidence that there is low thyroid activity present in the majority of chronic fatigue syndrome and fibromyalgia patients. [...] Studies demonstrate that in addition to an increased incidence of primary hypothyroidism in CFS, there is a combination of secondary, tertiary and thyroid resistance in the overwhelming majority of CFS patients, despite having normal thyroid tests.

On the other hand the Mayo clinic describes Chronic fatigue syndrome by saying:


The Mayo clinic also doesn't say anything about thyroid activity.

How good is the case that chronic fatigue syndrome is often caused by low thyroid activity?

  • Google scholar suggests there hasn't been much research to support this scholar.google.co.uk/scholar?hl=en&q=CFS+thyroid (note lack of clear trials and lack of citations). Deleted my answer as it was based on a digression to something more familiar and doesn't answer the question, sorry! – Dikran Marsupial Mar 15 '16 at 10:12
  • This study-ncbi.nlm.nih.gov/pubmed/19271598 shows that CFS does not lead to endocrine pathology. – pericles316 Mar 15 '16 at 12:07
  • @pericles316 according to google scholar, that paper has only seven citations (only 4 in web of science), which suggests the research community didn't find it compelling. – Dikran Marsupial Mar 15 '16 at 12:20

If we follow the Centers for Disease Control and Prevention's definition of chronic fatigue syndrom, a CFS diagnosis requires the following (among other) criterion to be fulfilled:


Since fatigue is one of the most common symptoms of hypothyroidism, a hypothyroidism diagnosis basically rules out a CFS diagnosis.

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  • That definition says that other conditions have to be ruled out by diagnostic tests. The argument is thyroid tests produce normal results in those cases but there are still thyroid problems. – Christian Mar 15 '16 at 11:22
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    @Christian How are these thyroid problems determined if not by using a diagnostic test? If you read the entire article (and not just the quoted part in the question), it is stated that the alleged thyroid problems in CFS subjects 'are not detected by standard thyroid function tests'. Even if hypothyroidism is determined with a non-standard test, it will rule out a CFS diagnosis. – Tor-Einar Jarnbjo Mar 15 '16 at 13:34
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    The "not detected by a standard thyroid function test" sounds like the sort of Occam's razor violation that is often used to try and keep a hypothesis alive in the face of scant supporting evidence, especially as there doesn't seem to be much in the way of published studies supporting the hypothesis and there are no references in the article. – Dikran Marsupial Mar 15 '16 at 15:37
  • @Tor-EinarJarnbjo The idea is that people who react positively to thryoid hormone supplementation have problems with low thyroid activity. – Christian Mar 15 '16 at 15:57
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    FWIW the wikipedia page for thyroid tests suggest that modern tests do measure (F)T3 as well as T4, so the article is perhaps out of date. Also as Tor-Einar suggests, if someones fatigue is improved by thyroid hormone supplementation, then by definition they don't have CFS as it is largely a diagnosis of exclusion. – Dikran Marsupial Mar 15 '16 at 17:14

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