The calciotropic hormone response to changes in serum calcium during exercise in female long distance runners.

The purpose of this study was to evaluate the effects of 45 min of submaximal running on calciotropic hormone levels in female long distance runners. Fourteen long distance runners and six sedentary controls (less than three exercise sessions per week) had bone mineral density (BMD) of the lumbar spine (L2-L4), femoral neck, and tibia measured by dual photon absorptiometry. All of the sedentary controls and eight runners (NormR) had BMD values within the normal range for women of their age. The remaining six runners had BMD L2-L4 measures greater than 1 SD below normal values and were classified as the low bone density group (LowR). Subjects were tested for their calciotropic hormone response to submaximal running using both an oral calcium load (dairy product), to induce a significant elevation in serum calcium, and no calcium load. In both exercise tests, serum calcium rose in NormR and LowR, with a greater increase induced by the oral calcium load. In NormR, the increase in serum calcium resulted in decreased PTH levels, with small increases in calcitonin levels. In contrast, LowR showed significant (P < 0.05) increases in PTH levels, with concurrent decreases in calcitonin levels. The changes in calciotropic hormone levels were shown to be significantly associated with BMD. Our results suggest that in well trained female runners with low spinal bone density, long distance running may aggravate this condition through the effect of exercise-related elevations of PTH on bone turnover. Alterations in the homeostatic control mechanisms for calcium during exercise should also be considered in the clinical assessment of female runners with spinal osteopenia.