Extended duration of vertical position might impair bone metabolism.
Bone-remodelling is markedly influenced by vectors of gravitational forces. Sleep-deprivation, common during military training, involves a change in the normal balance between horizontal and vertical forces enacting on the skeleton. Stress fractures are likewise prevalent among army recruits. In order to investigate the impact of sleep-deprivation on bone-metabolism, three groups of young, healthy volunteers were selected to exercise the following: 63 h of sleeplessness (17 participants, group A); vertical sleep in a seated position for three consecutive nights (9 participants, group B); controls who slept 6 h a night horizontally (14 participants, group C). During periods of wakefulness, all participants were kept in an upright position. Twenty-four hours' urine collection was strictly observed from two days prior to the experiment until two days after it (1 week). Changes in levels of the most characteristic bone-metabolites, calcium and hydroxyproline indicate an increased bone-resorption in the two experimental groups, but not in controls. The calcium excreted in the fasting urine peaked significantly at 72 h after the beginning of the experiment (+ 170% in group A; + 68% in group B, relative to the basal level). Qualitatively, similar results were obtained with hydroxyproline. On an individual basis, approximately 40% of the participants in either group responded by exceeding urinary-calcium elevation. A comparison of pre-test bone-density between responders and non-responders, reveals a significantly lower bone-density (-5%) in calcium and hydroxyproline excretors. These results suggest a pre-disposition to bone-resorption associated with responsiveness to changes in the balance between gravitational forces.
Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
S A
SA
Ben-Sasson
A
A
Finestone
M
M
Moskowitz
R
R
Maron
M
M
Weinner
I
I
Leichter
J
J
Margulies
P
P
Stein
M
M
Popovtzer
D
D
Rubinger
D000293:Adolescent; D015415:Biomarkers / Q000652:urine; D015519:Bone Density; D001862:Bone Resorption; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000652:urine; D005215:Fasting; D006801:Humans; D006909:Hydroxyproline / Q000652:urine; D008297:Male; D010758:Phosphorus / Q000652:urine; D011187:Posture; D012890:Sleep; D012892:Sleep Deprivation; D013314:Stress, Mechanical; D016683:Supine Position; D013997:Time Factors; D014851:Wakefulness
D015415:Biomarkers; D010758:Phosphorus; D006909:Hydroxyproline; D002118:Calcium