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This Article Full Text Full Text (PDF) All Versions of this Article: 107/2/540    most recent 91530.2008v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Trudel, G. Articles by Uhthoff, H. K. PubMed PubMed Citation Articles by Trudel, G. Articles by Uhthoff, H. K.

Bone marrow fat accumulation after 60 days of bed rest persisted 1 year after activities were resumed along with hemopoietic stimulation: the Women International Space Simulation for Exploration study

¹Bone and Joint Laboratory, University of Ottawa, Ottawa, Ontario; ²Philips Healthcare and Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada; ³United States Army Institute of Surgical Research, Fort Sam, Houston, Texas; ⁴Department of Clinical, Morphological and Technological Sciences, University of Trieste, Trieste, Italy; ⁵Département d'Ecologie, Physiologie et Ethologie, Strasbourg, France; and ⁶Cardiorespiratory and Vascular Dynamics Laboratory, University of Waterloo, Waterloo, Ontario, Canada

Submitted 2 December 2008 ; accepted in final form 26 May 2009

Immobility in bed and decreased mobility cause adaptations to most human body systems. The effect of immobility on fat accumulation in hemopoietic bone marrow has never been measured prospectively. The reversibility of marrow fat accumulation and the effects on hemopoiesis are not known. In the present study, 24 healthy women (age: 25–40 yr) underwent –6° head-down bed rest for 60 days. We used MRI to noninvasively measure the lumbar vertebral fat fraction at various time points. We also measured hemoglobin, erythropoietin, reticulocytes, leukocytes, platelet count, peripheral fat mass, leptin, cortisol, and C-reactive protein during bed rest and for 1 yr after bed rest ended. Compared with baseline, the mean (± SE) fat fraction was increased after 60 days of bed rest (+2.5 ± 1.1%, P < 0.05); the increase persisted 1 yr after the resumption of regular activities (+2.3 ± 0.8%, P < 0.05). Mean hemoglobin levels were significantly decreased 6 days after bed rest ended (–1.36 ± 0.20 g/dl, P < 0.05) but had recovered at 1 yr, with significantly lower mean circulating erythropoietin levels (–3.8 ± 1.2 mU/ml, P < 0.05). Mean numbers of neutrophils and lymphocytes remained significantly elevated at 1 yr (+617 ± 218 neutrophils/µl and +498 ± 112 lymphocytes/µl, both P < 0.05). These results constitute direct evidence that bed rest irreversibly accelerated fat accumulation in hemopoietic bone marrow. The 2.5% increase in fat fraction after 60 days of bed rest was 25-fold larger than expected from historical ambulatory controls. Sixty days of bed rest accelerated by 4 yr the normal bone marrow involution. Bed rest and marrow adiposity were associated with hemopoietic stimulation. One year after subjects returned to normal activities, hemoglobin levels were maintained, with 43% lower circulating erythropoietin levels, and leukocytes remained significantly elevated across lineages. Lack of mobility alters hemopoiesis, possibly through marrow fat accumulation, with potentially wide-ranging clinical consequences.

magnetic resonance imaging; erythropoietin; erythrocytes; leukocytes