There has recently been a lot of speculation regarding the use of medication for treating thyroid problems across the athletic population. It therefore seems fitting to try and grasp an understanding of the current issue surrounding the controversial stance of thyroid medication across athletes and why we should all be wary of the contrasting literature surrounding this topic.

Unsurprisingly, the controversy starts with a ‘medical consultant’ called Dr. Jeffrey S. Brown, an endocrinologist based in America. The term medical consultant is used loosely as in many interviews Dr. Brown refers to himself as a consultant to the United States of America Track and Field group and to the U.S. Olympic Committee; however both have said that he is not a consultant and Dr. Brown himself admits that the term medical consultant for these agencies is “loosely run”. But that’s another story.

Dr. Brown does work for Nike, and within this has treated many of Alberto Salazar’s athletes. In fact, out of the 30 athletes Salazar coaches, 5 have been treated by Dr. Brown with Hypothyroidism, including Galen Rupp and many athletes that are unnamed due to medical privacy rules.

The belief in the centre of all the scepticism is that when endurance athletes train hard this can induce an early onset of a thyroid hormonal imbalance called Hypothyroidism which involves a fatigue like condition that can prevent an athlete from performing at their peak. The medication for this is a synthetic thyroid hormone called Levothyroxine which helps to regulate the body’s metabolism. The diagnosis for Hypothyroidism is done using blood samples that measure another hormone, Thyroid Stimulating Hormone (TSH), which controls the production of the thyroid hormones. An increase in TSH means a decrease in thyroid hormone production and a large possibility that you have an underactive thyroid and need medication.

Based on the American College of Endocrinology Literature, the normal range of TSH is very broad, ranging from a low 0.5 to 5, with a TSH level of greater than 4 along with reported fatigue being enough to warrant medication for underactive thyroid, similar to the guidelines stated in the UK. However, Dr. Brown, stated as the best endocrinologist in the world by Salazar, argues that an underactive thyroid can be defined by a TSH level as low as 2. What’s more worrying than this fact is that Nike Inc. pay Dr. Brown to evaluate Nike athlete’s medical tests. I’m sure he does this really vigorously and reliably though.

Interestingly, an early study exploring performance and the effects of overtraining on a variety of hormones, including the thyroid hormones TSH, tri-iodothyronine (T3) and thyroxine (T4), showed no differences in the level of thyroid hormones through-out the study (Lehmann et al., 1992). 17 distance runners were physically over-trained as the main aim of this study in order to examine the impact of an exhaustively high volume and intensity training program on several hormones. Even with a plateau in endurance performance and maximum performance due to overtraining, thyroid hormone levels remained stable from baseline to training end. And this isn’t the only research to show the stability of thyroid hormones when training gets intense and the volume increases (Mujika et al., 1996).

More recently, an investigation on the relationship between thyroid hormones and common symptoms of overtraining were explored across 16 female track and field athletes (Nicoll, 2014). A 14 week descriptive study encompassed the beginning of indoor season and the end of outdoor season. There was a significant correlation between fatigue and running performance at week 12 suggesting overtraining. There were no significant changes in TSH, T3 and T4 from pre to post study. However, there were significant correlations between total caloric intake at the end of the study and hormones tri-iodothyronine (T3) and thyroxine (T4). This research is suggestive of the idea that changes in thyroid function in athletes may be primarily associated with decreased caloric intake. This was also noted in another study looking at sprinters, elite marathons runners and sedentary controls where the only significant difference between the groups was the ratio of TSH to free T3 which is independently associated with levels of leptin, the appetite hormone (Perseghin, 2009).

Conversely, there is evidence to show that an underactive thyroid, a lack of thyroid hormones, can cause sporting performance to decrease. An inverse correlation has been found between a thyroid hormone, triiodothyronine [T(3)], and VO2max which has shown that as the level of this thyroid hormone decreases, the VO2max of elite endurance athletes decreases when performing a 20 minute cycle ergometer test at 80% VO2max (Lucia, Hoyos, Pérez & Chicharro, 2001).

The contrasting evidence suggests that an underactive thyroid can debilitate performance, but is not necessarily caused by overtraining, as Dr. Brown would have athletes believe. Dr. Brown’s opinion is that excessive exercise causes a sufficient amount of stress on the body to cause underactive thyroid.  Based on the conflicting evidence, it should remain just an opinion.

Unfortunately, some athletes do actually have an underactive thyroid and need the medication. However, there is potential for athletes to be abusing this and using the medication to enhance performance as the thyroid hormone thyroxine is a stimulant. With a lack of evidence showing performance enhancements from underactive thyroid medication, just an unnerving amount of elite athletes taking the drug and performing well, it is unknown how and if the medication does produce such beneficial performance effects. What should definitely be considered is a tighter control over the diagnosis for such a condition and what constitutes as an underactive thyroid rather than a broad definition with regards to the level of hormones that seem to be interchangeable depending on who has the last word/opinion.






ReferencesShow all

Lucía, A., Hoyos, J., Pérez, M., & Chicharro, J. L. (2001). Thyroid Hormones May Influence the Slow Component of VO2 in Professional Cyclists. The Japanese journal of physiology, 51, 239-242.

Lehmann, M., Gastmann, U., Petersen, K. G., Bachl, N., Seidel, A., Khalaf, A. N., ... & Keul, J. (1992). Training-overtraining: performance, and hormone levels, after a defined increase in training volume versus intensity in experienced middle-and long-distance runners. British journal of sports medicine, 26, 233-242.

Mujika, I., Chatard, J. C., Padilla, S., Guezennec, C. Y., & Geyssant, A. (1996). Hormonal responses to training and its tapering off in competitive swimmers: relationships with performance. European journal of applied physiology and occupational physiology, 74, 361-366.

Nicoll, J. (2014). Thyroid hormones, performance, and psychological changes on overtraining in female distance runners.

Perseghin, G., Lattuada, G., Ragogna, F., Alberti, G., La Torre, A., & Luzi, L. (2009). Free leptin index and thyroid function in male highly trained athletes.European Journal of Endocrinology, 161, 871-876.