Influence of marathon running on thyroid hormones

Area of Science:

• Endocrinology
• Sports Physiology
• Exercise Science

Background:

• Thyroid hormones play a crucial role in regulating metabolism and energy balance.
• Prolonged strenuous exercise, such as marathon running, can induce significant physiological stress.
• Understanding the impact of endurance exercise on thyroid hormone dynamics is essential for athletes and clinicians.

Purpose of the Study:

• To investigate the changes in thyroid hormone levels and peripheral conversion during and after marathon running.
• To assess the impact of prolonged exercise on free thyroxine (fT4), free triiodothyronine (fT3), and reverse triiodothyronine (rT3).

Main Methods:

• Blood samples were collected from 16 male amateur runners before, immediately after, and 60 minutes and 22 hours post-marathon.
• Measurements included free thyroxine (fT4), thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), and free reverse triiodothyronine (frT3).
• Peripheral conversion of thyroxine was estimated using rT3/T3 and rT3/T ratios.

Main Results:

• Free thyroxine (fT4) levels significantly increased immediately after and 1 hour post-race.
• Thyroid-stimulating hormone (TSH) showed a transient increase immediately after the race, returning to baseline at 1 hour, and decreasing at 22 hours.
• Free reverse triiodothyronine (frT3) significantly increased, while free triiodothyronine (fT3) showed an insignificant decrease post-exercise. Peripheral conversion favored rT3 production, persisting for 22 hours.

Conclusions:

• Prolonged exercise stimulates TSH-regulated thyroxine (T4) secretion.
• A shift in peripheral conversion favors the production of the less active reverse triiodothyronine (rT3).
• These thyroid hormone alterations persist for an extended period (22 hours) after marathon running.