Effects of the Iditarod Sled Dog Race on serum thyroid hormones and body composition.

Cold exposure, activity and energy deficit have been associated with changes in body composition and/or changes in serum thyroid hormones. Because these conditions are present during the Iditarod Sled Dog Race, 10 volunteer participants were studied before and after the race. Body composition, total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), and free triiodothyronine (FT) levels were determined. There was a significant decrease in body weight (p < 0.05) and a decrease in body fat (p < 0.01). There were no significant changes in TT4, FT4, TT3 or FT3. On the basis of this study, it can be concluded that the strenuous activity of the Iditarod mitigates against the classic perturbation in thyroid axis brought on by the hypocaloric state.