Maintenance of Serum Ionized Calcium During Exercise Attenuates Parathyroid Hormone and Bone Resorption Responses.
Level 2 - randomized trial
Small controlled crossover physiological trial in humans.
PubMed 29572961 · doi:10.1002/jbmr.3428
What was done
Eleven cycling-trained men aged 18 to 45 years completed two identical 60-minute cycling sessions receiving either an intravenous calcium gluconate clamp (to maintain serum ionized calcium, iCa) or a saline control infusion. Blood was collected before, during, and for 4 hours after exercise to assess iCa, total calcium (tCa), parathyroid hormone (PTH), carboxy-terminal collagen crosslinks (CTX, a resorption marker), and procollagen type 1 amino-terminal propeptide (P1NP, a formation marker), analyzed both unadjusted and adjusted for plasma volume changes.
What was found
During saline infusion, serum iCa declined during exercise (p = 0.01 at 60 min), whereas calcium infusion prevented this drop (interaction p < 0.007). Both conditions exhibited early decreases in plasma-volume-adjusted calcium content within the first 15 minutes. At the end of exercise, saline led to increases in PTH and CTX (both p < 0.01), which were substantially attenuated by calcium infusion (-65% for PTH and -71% for CTX; both p < 0.001). CTX remained elevated for 4 hours post-exercise in the saline condition (p < 0.001) even after PTH normalized at 1 hour. Unadjusted P1NP increased with exercise (p < 0.001) across both trials, but plasma-volume-adjusted P1NP changes were not significant.
Why it matters
This study demonstrates that acute exercise-induced bone resorption is a rapid compensatory response to defend circulating ionized calcium. Preventing the drop in ionized calcium substantially reduces the catabolic PTH and bone resorption response during endurance exercise.
Limits
The trial had a very small sample size (n = 11) restricted entirely to trained young-to-middle-aged men, limiting generalizability to women, older adults, and untrained individuals. The observation window was limited to 4 hours post-exercise, leaving potential delayed anabolic effects unmeasured, and the precise physiological sink or mechanism driving the rapid loss of vascular calcium in early exercise was not identified.
Cited by
- supports Wendy Kohrt's research in Colorado showed that exercise onset causes blood calcium levels to drop, stimulating parathyroid hormone release and subsequent leaching of calcium from bones.