Response of Parathyroid Hormone to Exercise and Bone Mineral Density in Adolescent Female Athletes

Background：This study investigates 1) the effects of amount of exercise on levels of serum parathyroid hormone (PTH) and calcium, and 2) the relationship between PTH response and bone mineral density in adolescent female athletes. Subjects：Twenty-one female athletes on a top-ranked high school basketball team in Japan participated in a one-month intensive basketball program. Subjects were divided into moderate-exercise and strenuous-exercise groups. Methods：The amount of exercise was quantified using estimated metabolic equivalent (METs) and exercise hours. Levels of serum intact-PTH and calcium were examined five times： twice before training to establish a baseline (T_-1 and T_0 ), once 3rd week of the training period (T_1 ), once immediately at the end of the program (T_2 ), and again one week later (T_3 ). Bone mineral density of forearm (distal-BMD) was measured one week after the end of the program. PTH levels at T_1 , T_2 and T_3 were regressed on PTH at baseline (T_0 ) for both groups and examined for statistical significance. Multiple regression analyses of the changes of PTH and distal-BMD were conducted. Results：1) Strenuous-exercise subjects showed both increased and decreased PTH levels, while moderate-exercise subjects showed a uniform decrease in PTH throughout the exercise period. 2) Increased PTH was an independent negative predictor of distal-BMD, while high lean body mass, increased serum Ca, and exercise volume were positive predictors. Conclusion：The amount of exercise affects PTH response： moderate exercise suppresses PTH secretion, while strenuous exercise is apt to induce continuous secretion, which has a negative effect on BMD.