New approaches needed to prevent bone loss in women during bed-rest
MedWire News: More research is required into methods for preventing bone loss in women during prolonged bed-rest, show WISE-2005 study results.
The Women International Space Simulation for Exploration study (WISE-2005) conducted a bed-rest study to investigate bone loss, a serious problem in astronauts, presumed to be caused by reduced loading of the skeleton under conditions of minimal gravity. These studies are important clinically, as well as for the space exploration industry, especially regarding patient rehabilitation after long periods of bed-rest.
Previous studies have focused on men, so the authors of this study, published in the journal Bone, chose to investigate the under-studied female physiologic response to simulated weightlessness.
Twenty-four healthy women, aged 25 to 40 years, were confined to 60 days of 6° head-down tilted bed-rest and two methods of preventing bone loss were tested. The patients were divided into three equal groups - one testing the effects of taking an exercise regime during this period, one testing a high-protein diet, and the other a control group.
Bone mineral density (BMD) was measured using peripheral quantitative computed tomography and dual-X-ray absorptiometry at nine different time points - the first at baseline, then at three points during the bed-rest period, and at 3, 45, 90, 180, and 360 days after the bed-rest was completed.
Significant BMD losses occurred at the tibia, total hip, lumbar spine, whole-body trunk, and whole-body leg during bed-rest, as well as reductions in cross-sectional area at the calf muscle and forearm muscle. Bone loss was greatest at the distal tibia and proximal femur and some of the BMD changes persisted up to 1 year after bed-rest. The trabecular tibia and the total hip values differed the most between baseline and 360 days after the bed-rest period was complete - the BMD values had decreased by 0.41% and 0.40%, respectively.
"The pattern of bone loss was similar to that seen in men in other studies in bed-rest, though the data provide some sex difference, for example at the distal radius," say Gisela Beller (Center of Muscle and Bone Research, Berlin, Germany) and team. They found that distal radius trabecular BMD appears to be particularly affected in women during inactivity, which is interesting considering there is evidence to suggest distal radius fractures are more common in women than in men.
Beller et al had expected that exercise might reduce the BMD losses, but they found neither of the two counter-measures had a significant effect on BMD.
Their results conflict with those of another group who used the same participants and found that hip and leg subregion BMD loss was significantly less in the exercise group. Beller and team are unable to find a reason for this discordance, but note that the study does have some important limitations, predominantly the small number of participants.
The researchers therefore conclude that "the countermeasures as implemented were not optimal in preventing bone loss during bed-rest and further development is required."
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By Chloe McIvor