The Study
Extrathyroidal conversion of thyroxine to 3,3',5'-triiodothyronine (reverse-T3) and to 3,5,3'-triiodothyronine (T3) in humans.
This study looked at how the body breaks down thyroid hormones in 11 people — 6 healthy and 5 on medicine. It found that both groups made similar amounts of certain hormones, so it suggests that the body might make most of them outside the thyroid. But it doesn’t prove that’s why someone feels sick or healthy — it just shows a pattern.
Analysis score
Maximum 44 for a cross-sectional study.
Where the score came from
Your body turns thyroid hormone into two forms: one that works (T3) and one that doesn't (reverse-T3). This study found that more of the hormone becomes the useless kind.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 544 / 100
Quality score
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — if most of your thyroid hormone turns into an inactive form, it could mean your cells aren't getting enough active signal, even if blood tests look normal.
- 2The body makes about 34 micrograms of reverse-T3 per day and 20-24 micrograms of active T3 per day.
- 3Reverse-T3 made up 57-62% of all T3-like molecules.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
The Journal of clinical endocrinology and metabolism
Year
1977
Authors
Laurence A. Gavin, James N. Castle, F. McMAHON, P. Martin, Margaret E. Hammond, R. R. Cavalieri
Related Content
Claims (5)
The thyroid hormone T4 can be converted into reverse T3, a molecule that binds to thyroid hormone receptors without activating them, which reduces the overall effect of active thyroid hormone on cells.
In both people with hypothyroidism and healthy individuals, reverse-T3 makes up about 62% and 57% respectively of the total amount of triiodothyronine in the blood.
In adult humans, about 34 micrograms of reverse-T3 are produced daily from thyroxine, which is similar to the amount of T3 produced daily (20-24 micrograms), showing that the conversion of thyroxine outside the thyroid gland is a major source of both hormones.
In people with hypothyroidism and in healthy individuals, the body produces reverse-T3 at nearly the same rate: about 34.3 micrograms per day and 33.0 micrograms per day, respectively.
The body converts the thyroid hormone T4 into two different forms: T3, which increases metabolic rate, and reverse T3, which does not. The relative amounts of these two forms determine how active metabolism is.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.