The Study
Thyroid Hormone Deiodination and Action in the Gonads.
This study is like a summary of other people’s experiments with mice and a few women — it says, 'Hey, when thyroid hormones change, the testes and ovaries sometimes act differently.' But it didn’t do any experiments itself, so we can’t say thyroid hormones definitely cause those changes.
Analysis score
Maximum 5 for a narrative review.
Where the score came from
Your thyroid hormone is like a traffic light for baby testicles: too much stops growth, too little lets cells keep dividing. A special enzyme (DIO3) turns off the hormone locally so testicles grow right. If the hormone gets in too easily (MCT8), testicles get too big. In women, low thyroid signals in the ovary link to lower fertility signs.
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 51 / 100
Quality score
Based on clinical experience or non-systematic literature reviews. The lowest level of evidence as they are most susceptible to bias and personal perspective.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — these changes in testicle size and hormone signals can lead to infertility in adulthood.
- 2In mice: No DIO3 → smaller testicles; No MCT8 → bigger testicles; No THRA → fixes oversized testicles.
- 3In women: Low thyroid receptors → lower gremlin-1 and prostaglandin synthase 2.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Current opinion in endocrine and metabolic research
Year
2018
Authors
Arturo Hernandez
Related Content
Claims (3)
Thyroid hormone doesn’t directly make sex hormones like testosterone or estrogen, but it helps the body’s sex glands work properly so they can produce these hormones at the right levels.
When baby rats don't have a special protein called MCT8 that helps thyroid hormone get into cells, their testicles grow bigger and keep growing longer than normal—suggesting this protein usually helps stop testicles from getting too big too fast.
In mice and rats, a specific protein called THRA is the main way thyroid hormone works in the testes. If this protein is missing or broken, the damage caused by too much thyroid hormone goes away—meaning THRA is needed for the hormone to affect the cells that make sperm and testosterone.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.