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Changes in bone turnover markers during 14-day 6 degrees head-down bed rest.
Hyeteok Kim1, Kenichi Iwasaki, Takeo Miyake
1Department of Hygiene and Space Medicine, Nihon University School of Medicine, 30-1 Oyaguchi-kamimachi, 173-8610 Tokyo, Itabashi-ku, Japan.
Journal of Bone and Mineral Metabolism
|August 21, 2003
Summary
Microgravity accelerates bone loss by increasing bone resorption markers like deoxypyridinoline (Dpyr) and type I collagen cross-linked N-telopeptides (NTx) early on, while bone formation markers show a decrease or remain unchanged.
Area of Science:
- Space medicine
- Bone physiology
- Biochemistry
Background:
- Microgravity-induced osteoporosis is a significant clinical issue.
- The precise mechanisms driving bone loss in microgravity are not fully understood.
- Detailed time-course data on bone resorption markers are limited.
Purpose of the Study:
- To investigate the impact of simulated microgravity on bone turnover.
- To specifically examine changes in bone resorption markers, deoxypyridinoline (Dpyr) and type I collagen cross-linked N-telopeptides (NTx).
Main Methods:
- Simulated microgravity using 6-degree head-down bed rest for 14 days.
- Eleven adult male volunteers participated.
- Measured serum and urine calcium, osteocalcin (OC), bone alkaline phosphatase (ALP), NTx, and Dpyr.
Main Results:
- Bone alkaline phosphatase (a marker of bone formation) significantly increased.
- Osteocalcin (a marker of bone formation) tended to decrease.
- Deoxypyridinoline (Dpyr) and NTx (bone resorption markers) significantly increased from early time points.
- Serum and urinary calcium levels increased by the end of the study.
Conclusions:
- Simulated microgravity leads to increased bone resorption and normal or reduced bone formation, causing significant bone loss.
- Bone resorption is enhanced early in exposure to microgravity.
- Bone ALP and OC serve as early and late markers, respectively, for osteoblast differentiation and bone formation phases.