The impact of exercise on thyroid hormone metabolism in children and adolescents.

Thyroid hormones are important regulators of energy metabolism and may influence energy processes during physical exercise. There are controversial results concerning thyroid hormone metabolism during strenuous exercise in adult athletes and only scant data concerning the impact of strenuous exercise on thyroid hormone metabolism in children and adolescents. Although some studies demonstrate a transient change in thyroid hormones during intense physical performance, most studies agree that these changes are of minor impact, practically reflecting the relative negative energy balance during strenuous exercise. This state of hypometabolism during intense physical performance has also been confirmed in highly trained female young athletes, who may be also characterized by reproductive axis dysfunction, manifested either as luteal-phase deficiency or amenorrhea, alongside the typical constellation of low T3, insulin and leptin levels. More importantly, strenuous exercise during childhood or adolescence is mostly accompanied by a delay of skeletal maturation, and height and may have a long-lasting negative effect on growth and acquisition of maximum bone mass. In conclusion, although thyroid hormones are only transiently or insignificantly changed during strenuous exercise, adequate caloric intake should be guaranteed in highly performing young athletes in order to counteract the relative negative energy balance and prevent alterations in endocrine-metabolic profile. Moreover, when growth and pubertal progression in very young athletes are significantly impaired, a reduction in the intensity of the physical exercise should be advocated in order to guarantee better final height and adequate acquisition of bone mass.