Thyroid hormones and stroke, the gap between clinical and experimental studies

Despite plenty of human studies on changes in thyroid hormones after stroke and some animal studies that assessed the effects of thyroid hormone administration on stroke, conclusive evidence for clinical application is lacking. This review aimed to determine the consistency of the results between clinical and preclinical studies. This article reviewed the PubMed, Embase, web of Knowledge, and Google Scholar databases up to June 2023 using the MeSH terms “stroke, cerebral ischemia, cerebral infarction, brain ischemia, brain infarction, triiodothyronine (T₃), tetraiodothyronine (T₄), thyroxine (T₄), and thyroid hormone". The results of clinical and preclinical studies related to T₃ substantially confirm each other. That is, in most human studies lower T₃ was associated with poor outcomes, and in experimental studies, T₃ administration also had therapeutic effects. However, the results of experimental studies related to T₄ could not support those of clinical studies. There seem to be some conflicts between experimental and human studies, especially regarding changes and effects of T₄ after stroke. The gap between experimental and clinical studies may lead to non-applicable results, wasting time and money, and unnecessary killing of animals.