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Title: Calcium kinetics during bed rest with artificial gravity and exercise countermeasures

Author
item SMITH, S - National Aeronautics And Space Administration (NASA)
item CASTANEDA-SCEPPA, C - Northeastern University
item O'BRIEN, K - Cornell University
item ABRAMS, S - Children'S Nutrition Research Center (CNRC)
item GILLMAN, P - Enterprise Advisory Services
item BROOKS, N - University Of Stirling
item CLOUTIER, G - Northeastern University
item HEER, M - University Of Bonn
item ZWART, S - Universities Space Research Associaton
item WASTNEY, M - Metabolic Modeling Services

Submitted to: Osteoporosis International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2014
Publication Date: 9/2/2014
Citation: 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. 2014. Calcium kinetics during bed rest with artificial gravity and exercise countermeasures. Osteoporosis International. 25(9):2237-2244.

Interpretive Summary: Bone health is a major concern to NASA researchers, particularly for their astronauts when traveling in space, but is also a concern that physicians and pediatricians have for the general public who lead a very sedentary lifestyle. We have collaborated with scientists at NASA to help understand bone health during space which is important for understanding bone health on earth in all populations, including children. In this study, volunteers were put to bed rest for an extended time to simulate long-term space flight. During this time, they were provided with a healthy diet and allowed to exercise. We helped the NASA scientists study if the diet and exercise helped prevent them from losing calcium by performing stable isotope studies of calcium use by the body. We found that the subjects lost extra calcium during bed rest even with exercise and that keeping a high intake of calcium was important for their bone health. This is critical as bone lost during both space flight and sedentary behavior can lead to lower peak bone mass in adolescents and increased osteoporosis in the elderly.

Technical Abstract: 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.