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Written by: Jeffrey Sankoff, MD
When triathletes toe the start line of a race, they often run through a mini-diagnostic checklist in their heads. How do the legs feel? Shoulders OK for the swim? Breathing comfortably? These are all useful insights into how the day is going to unfold, but only a very small group of triathletes adds questions about their blood sugar or resting metabolic rate to that list. This group faces some added challenges related to endocrine dysfunction.
The endocrine system is made up of a number of glands and hormones. The principal function of the system is to ensure that no matter what the body is doing, the internal milieu remains very stable. Glands respond to subtle changes in the internal milieu by increasing or decreasing the output of hormones that have far-reaching effects. The endocrine system regulates body temperature by varying basal metabolic rate, and maintains the concentrations of electrolytes and sugar in the blood stream in an incredibly narrow range. Normally the endocrine system is silent, but when things go awry, the results can be devastating and have a significant effect on quality of life.
Endocrine dysfunction may arise because a gland does not respond appropriately, a gland does not secrete a hormone or the hormone does not have its usual effect on its target cells. The most common endocrinopathy relates to dysfunction of the thyroid gland, which sits in front of the trachea just below the voice box in the neck.
Thyroid hormone has wide-ranging effects throughout the body that include regulation of the basal metabolic rate. An increased amount of thyroid hormone results in higher metabolism manifested as increased heart rate, body temperature and blood pressure. Too-low concentrations have the opposite effects. Various diseases affect the thyroid gland and cause it to malfunction, but the most common is autoimmune thyroiditis (Hashimoto’s thyroiditis).
Autoimmune thyroiditis affects women more commonly than men and tends to have a peak onset in the third and fourth decades of life. The initial inflammatory process is often completely asymptomatic but eventually results in destruction of the gland and the development of hypothyroidism. As thyroid hormone levels decrease, patients become progressively fatigued, gain weight and have changes in their hair and skin. While there is no cure for thyroiditis, hypothyroidism is easily treated by supplementing thyroid hormone with synthetic hormone pills. The difficulty comes in making the diagnosis, which is often delayed because of the insidious nature of the disease.
Conversely, autoimmune processes can also result in overstimulation of the thyroid gland, resulting in hyperthyroidism. The disease process in which antibodies attach to the thyroid gland and cause the release of thyroid hormone is called Grave’s disease. The resulting excess of thyroid hormone causes increased body temperature and higher heart rate, often with palpitations and weight loss.
Another cause of hyperthyroidism is inappropriate thyroid hormone supplementation. At its extreme, hyperthyroidism can become thyroid storm and may be life threatening. Fortunately, this is exceedingly rare and—with proper monitoring of thyroid function—is easy to avoid.
The endocrine system is inconspicuous until it ceases to work properly. The signs and symptoms of endocrinopathy, and especially of hypo- or hyperthyroidism, may be subtle and only manifest over a prolonged period of time, which delays diagnosis and treatment. For this reason, triathletes should regularly take stock of how they feel and of how they are responding to training and racing. Sometimes if things don’t feel right, it is because they are not. And in these instances, a doctor visit with appropriate testing may go a long way toward getting them back on track.