Thyroid metabolism and supplementation: A review framed in sports environment

Objectives This paper aimed to consider those features that may suggest a link between thyroid hormones pharmacology and athletes' health based on current consumption trends in a population of athletes. Methods Methods used were observation, description, and synthesis, mainly. Among the documents reviewed were books, scientific articles, and review articles peer‐reviewed. The review covered sources published in the period 1961 to 2021. Only references with a traceable origin were accepted (DOI numbering, ISSN, and ISBN, as well as peer‐reviewed journals). The data on the consumption of thyroid hormones derivatives were extracted from the Doping Control Forms of athlete samples received at Laboratorio Antidoping FMSI of Rome from 2017 to 2021. Results An overview of the biosynthesis, pharmacology, and metabolism of thyroid hormones, including thyronamines and thyronacetic acids, was presented. Likewise, a summary is presented on the relationship between thyroid hormones and ethnic and gender differences, their physiology in sport, and the reasons why their use could be considered attractive for athletes. Conclusion Today, thyroid hormones are not listed as a prohibited substance by the World Anti‐Doping Agency. However, several requests to include levothyroxine on the prohibited list are documented. The observation that the number of athletes taking thyroid hormones is growing, particularly in sports such as cycling, triathlons, and skating, should prompt an update on this topic. The ability of exogenous thyroid hormone to enhance metabolism is an attractive feature, especially in sports where the need of controlling weight and the increment of caloric expenditure is priority. Its metabolism is linked to IGF‐1, erythropoiesis, and GH, which are prohibited substances. Also, the unnecessary administration of thyroid supplementation can trigger a cardiovascular decompensation, among others. Should sports authorities be concerned by the increase of thyroid supplementation?