On the combined effects of normobaric hypoxia and bed rest upon bone and mineral metabolism: Results from the PlanHab study

Rittweger, Jörn; Debevec, Tadej; Frings-Meuthen, Petra; Lau, Patrick; Mittag, Uwe; Ganse, Bergita; Ferstl, Philip G.; Simpson, Elizabeth J.; Macdonald, Ian A.; Eiken, Ola; Mekjavic, Igor B.

Abstract

Bone losses are common as a consequence of unloading and also in patients with chronic obstructive pulmonary disease (COPD). Although hypoxia has been implicated as an important factor to drive bone loss, its interaction with unloading remains unresolved. The objective therefore was to assess whether human bone loss caused by unloading could be aggravated by chronic hypoxia. In a cross-over designed study, 14 healthy young men underwent 21-day interventions of bed rest in normoxia (NBR), bed rest in hypoxia (HBR), and hypoxic ambulatory confinement (HAmb). Hypoxic conditions were equivalent to 4000m altitude. Bone metabolism (NTX, P1NP, sclerostin, DKK1) and phospho-calcic homeostasis (calcium and phosphate serum levels and urinary excretion, PTH) were assessed from regular blood samples and 24-hour urine collections, and tibia and femur bone mineral content was assessed by peripheral quantitative computed tomography (pQCT). Urinary NTX excretion increased (P<0.001) to a similar extent in NBR and HBR (P=0.69) and P1NP serum levels decreased (P=0.0035) with likewise no difference between NBR and HBR (P=0.88). Serum total calcium was increased during bed rest by 0.059 (day D05, SE 0.05mM) to 0.091mM (day D21, P<0.001), with no additional effect by hypoxia during bed rest (P=0.199). HAmb led, at least temporally, to increased total serum calcium, to reduced serum phosphate, and to reduced phosphate and calcium excretion. In conclusion, hypoxia did not aggravate bed rest-induced bone resorption, but led to changes in phospho-calcic homeostasis likely caused by hyperventilation. Whether hyperventilation could have mitigated the effects of hypoxia in this study remains to be established.

Citation

Rittweger, J., Debevec, T., Frings-Meuthen, P., Lau, P., Mittag, U., Ganse, B., …Mekjavic, I. B. (2016). On the combined effects of normobaric hypoxia and bed rest upon bone and mineral metabolism: Results from the PlanHab study. BONE, 91, 130-138. https://doi.org/10.1016/j.bone.2016.07.013

• Journal Article Type: Article
• Acceptance Date: Jul 17, 2016
• Online Publication Date: Jul 27, 2016
• Publication Date: 2016-10
• Deposit Date: Jan 20, 2023
• Publicly Available Date: Jan 23, 2023
• Journal: Bone
• Print ISSN: 8756-3282
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 91
• Pages: 130-138
• DOI: https://doi.org/10.1016/j.bone.2016.07.013
• Keywords: Physiology; Endocrinology, Diabetes and Metabolism; Histology
• Public URL: https://nottingham-repository.worktribe.com/output/1360896
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S8756328216301934?via%3Dihub
• Additional Information: This article is maintained by: Elsevier; Article Title: On the combined effects of normobaric hypoxia and bed rest upon bone and mineral metabolism: Results from the PlanHab study; Journal Title: Bone; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.bone.2016.07.013; Content Type: article; Copyright: © 2016 The Author(s). Published by Elsevier Inc.