Smith S M, Castaneda-Sceppa C, O'Brien K O, Abrams S A, Gillman P, Brooks N E, Cloutier G J, Heer M, Zwart S R, Wastney M E
NASA Lyndon B. Johnson Space Center, Attn: Mail Code SK3, 2101 NASA Parkway, Houston, TX, 77058, USA,
Osteoporos Int. 2014 Sep;25(9):2237-44. doi: 10.1007/s00198-014-2754-x. Epub 2014 May 27.
We assessed the potential for countermeasures to lessen the loss of bone calcium during bed rest. Subjects ingested less calcium during bed rest, and with artificial gravity, they also absorbed less calcium. With exercise, they excreted less calcium. To retain bone during bed rest, calcium intake needs to be maintained.
This study aims to assess the potential for artificial gravity (AG) and exercise (EX) to mitigate loss of bone calcium during space flight.
We performed two studies: (1) a 21-day bed rest (BR) study with subjects receiving 1 h/day AG (n = 8) or no AG (n = 7) and (2) a 28-day BR study with 1 h/day resistance EX (n = 10) or no EX (n = 3). In both studies, stable isotopes of Ca were administered orally and intravenously, at baseline and after 10 days of BR, and blood, urine, and feces were sampled for up to 14 days post dosing. Tracers were measured using thermal ionization mass spectrometry. Data were analyzed by compartmental modeling.
Less Ca was absorbed during BR, resulting in lower Ca balance in BR+AG (-6.04 ± 3.38 mmol/day, P = 0.023). However, Ca balance did not change with BR+EX, even though absorbed Ca decreased and urinary Ca excretion increased, because endogenous excretion decreased, and there was a trend for increased bone deposition (P = 0.06). Urinary N-telopeptide excretion increased in controls during BR, but not in the EX group. Markers of bone formation were not different between treatment groups for either study. Ca intake decreased during BR (by 5.4 mmol/day in the AG study and 2.8 mmol/day in the EX study), resulting in lower absorbed Ca.
During BR (or space flight), Ca intake needs to be maintained or even increased with countermeasures such as exercise, to enable maintenance of bone Ca.
我们评估了采取应对措施以减少卧床休息期间骨钙流失的可能性。受试者在卧床休息期间摄入的钙较少，并且在有人造重力的情况下，他们吸收的钙也较少。进行锻炼时，他们排出的钙较少。为了在卧床休息期间保持骨骼健康，需要维持钙的摄入量。
本研究旨在评估人造重力（AG）和锻炼（EX）减轻太空飞行期间骨钙流失的可能性。
我们进行了两项研究：（1）一项为期21天的卧床休息（BR）研究，受试者每天接受1小时人造重力（n = 8）或不接受人造重力（n = 7）；（2）一项为期28天的卧床休息研究，每天进行1小时抗阻锻炼（n = 10）或不进行锻炼（n = 3）。在两项研究中，在基线时以及卧床休息10天后，通过口服和静脉注射给予钙的稳定同位素，给药后长达14天采集血液、尿液和粪便样本。使用热电离质谱法测量示踪剂。通过房室模型分析数据。
卧床休息期间钙的吸收较少，导致卧床休息加人造重力组（BR+AG）的钙平衡较低（-6.04±3.38毫摩尔/天，P = = 0.023）。然而，尽管卧床休息加锻炼组（BR+EX）吸收的钙减少且尿钙排泄增加，但钙平衡并未改变，因为内源性排泄减少，并且骨沉积有增加的趋势（P = = 0.06）。卧床休息期间，对照组的尿N-端肽排泄增加，但锻炼组没有。两项研究中，各治疗组之间的骨形成标志物没有差异。卧床休息期间钙摄入量减少（在人造重力研究中减少5.4毫摩尔/天，在锻炼研究中减少2.8毫摩尔/天），导致吸收的钙减少。
在卧床休息（或太空飞行）期间，需要维持甚至通过锻炼等应对措施增加钙的摄入量，以维持骨钙水平。
