Thyroid Function and Exercise

Abstract

Thyroid hormone receptors are present in virtually every tissue in the body, thereby permitting an important physiologic role for the two thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Skeletal and cardiac muscle function, pulmonary performance, metabolism, and the neurophysiologic axis are only a few of the important areas that are affected by thyroid hormone levels (1). Any abnormality in thyroid function causing either an excess or deficiency in circulating thyroid hormone levels can lead to changes in body function at rest and during exercise. The presence of thyroid disease can have a major impact on exercise tolerance resulting in reduced performance of strenuous activities. On the other hand, exercise itself may have direct or indirect effects on thyroid function, either secondary to acute alterations in the integrity of the pituitary—thyroid axis or to the more long-lasting changes noted in well-trained athletes to be discussed below. Alterations in thyroid function in well-trained athletes might be viewed as an adaptive mechanism associated with enhanced performance possibly serving to provide a better balance between energy consumption and expenditure. Underlying energy balance does appear to play an important role in the effects exercise may have on the pituitary and thyroid axis. Reports in the literature indicate that athletes with excessive weight loss may exhibit a “low T3 syndrome” accompanied by amenorrhea (in women) as well as other alterations in pituitary function (2). Fortunately, thyroid diseases usually can be treated effectively, and most individuals with thyroid disorders should expect to obtain resolution of their thyroid-related symptoms, including those associated with a negative impact on their exercise tolerance. Gail Devers, who has been very public about her experience with Graves’ disease, is a well-known sprinter who went on to win Olympic fame following treatment for her Graves’ disease and may act as a case in point.