Can Exercise Increase Thyroid Function?

Your thyroid gland, located in your throat, is an important regulator of metabolism that affects how your body responds to exercise. Exercise acutely raises thyroid hormone levels. While the longer term effects of exercise training are less clear, in general, people who exercise tend to have normal levels of thyroid hormones as long as they consume sufficient calories to fuel their workouts.

The Thyroid Gland

The thyroid gland is located on the front of the neck, just below the larynx. When prompted by thyroid-stimulating hormone, which is secreted by the pituitary gland, the thyroid releases hormones into the bloodstream. Thyroid hormones affect most cells of the body by stimulating metabolism. People who have low concentrations of thyroid hormone tend to have a sluggish metabolism, while those with excessive concentrations have an accelerated metabolism.

Thyroid Hormones

The two types of thyroid hormone are thyroxine, or T4, and triiodothyronine, or T3. Most thyroid hormone released by the thyroid is T4, but T3 is the more active form. Most tissues in the body are able to convert T4 into T3. Most thyroid hormone circulating in the blood is bound to other proteins, but some also circulates in a free form which can be easily taken up by tissues.

Effects of Thyroid Hormone

Thyroid hormones play a major role in how your body responds to exercise. T3 encourages muscle growth by stimulating the turnover of old proteins and the synthesis of new protein. It also affects muscle fiber type. Low levels of T3 cause a shift toward more slow-twitch fibers, whereas high levels lead to more fast-twitch fibers. T3 also affects the way muscle fibers contract. Low levels of thyroid hormone can reduce the speed and power of your muscles.

Effects of Exercise on Thyroid Function

Exercising at low intensity increases blood levels of T3, T4 and TSH. As intensity rises, T3 concentrations decrease and TSH and T4 continue to rise, although the reasons for this are not well understood. The longer-term effects of exercise on thyroid function are also unclear and seem to depend on an individual's level of training. In general, thyroid hormone concentrations among exercisers remain within normal, healthy limits. However severely cutting your caloric intake while maintaining a strenuous exercise program could lead to reduced thyroid hormone concentrations.