PLAY
Parathyroid hormone (PTH) is the primary regulator of calcium and phosphate homeostasis, secreted by the parathyroid glands in response to low blood calcium. (source) It acts on the kidneys (to retain calcium and activate vitamin D), bones (to mobilize calcium from bone mineral), and intestines (indirectly via vitamin D to enhance calcium absorption) — maintaining the narrow calcium range required for normal muscle contraction, nerve signaling, and cellular function.
For performance, PTH is a critical monitor of skeletal integrity and calcium metabolism. Chronically elevated PTH — whether from vitamin D deficiency, low dietary calcium, or primary hyperparathyroidism — drives continuous calcium mobilization from bone. (source) This increases fracture risk, impairs bone adaptation to training, and undermines the structural foundation needed for high-load exercise. (source)
