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Calcium absorption, endogenous excretion, and endocrine changes during and after long-term bed rest
A LeBlanc1, V Schneider, E Spector
1Department of Medicine, Baylor College of Medicine, Houston, TX, USA.
Bone
|April 1, 1995
Summary
Bed rest causes negative calcium balance, increasing fecal and urine calcium. Reduced calcium absorption, not increased excretion, is the primary cause, with bone formation rebounding after immobilization.
Area of Science:
- Human physiology
- Bone metabolism
- Mineral balance
Background:
- Negative calcium balance is a known consequence of prolonged bed rest.
- This imbalance is characterized by increased urinary and fecal calcium excretion.
- The precise mechanisms, including absorption and endogenous excretion, require further elucidation.
Purpose of the Study:
- To quantify calcium absorption and endogenous fecal excretion before and during prolonged bed rest.
- To investigate the impact of bed rest on calcium homeostasis and bone turnover markers.
- To understand the recovery of calcium balance post-bed rest.
Main Methods:
- Employed dual or single isotope methods combined with calcium balance studies.
- Measured true calcium absorption and endogenous fecal excretion in eight healthy male volunteers.
- Monitored serum and urinary markers of calcium metabolism and bone turnover.
Main Results:
- Calcium absorption significantly decreased during bed rest (31% to 24%), while fecal calcium increased.
- Urinary calcium excretion also rose during bed rest.
- Markers of bone formation (alkaline phosphatase, osteocalcin) were elevated during reambulation, suggesting bone formation rebound.
Conclusions:
- Reduced calcium absorption is the main driver of negative calcium balance during bed rest.
- Bone metabolism shows a rebound in formation following immobilization and return to ambulation.
- Individual variations in calcium excretion mechanisms exist.