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J Appl Physiol 99: 134-140, 2005. First published February 3, 2005; doi:10.1152/japplphysiol.01406.2004
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Amino acid supplementation alters bone metabolism during simulated weightlessness

S. R. Zwart,1 J. E. Davis-Street,2 D. Paddon-Jones,3 A. A. Ferrando,3 R. R. Wolfe,3 and S. M. Smith1

1Human Adaptation and Countermeasures Office, National Aeronautics and Space Administration Lyndon B. Johnson Space Center, and 2Enterprise Advisory Services, Inc., Houston, Texas; and 3Departments of Surgery and Anesthesiology, University of Texas Medical Branch at Galveston, Galveston, Texas

Submitted 22 December 2004 ; accepted in final form 28 January 2005

High-protein and acidogenic diets induce hypercalciuria. Foods or supplements with excess sulfur-containing amino acids increase endogenous sulfuric acid production and therefore have the potential to increase calcium excretion and alter bone metabolism. In this study, effects of an amino acid/carbohydrate supplement on bone resorption were examined during bed rest. Thirteen subjects were divided at random into two groups: a control group (Con, n = 6) and an amino acid-supplemented group (AA, n = 7) who consumed an extra 49.5 g essential amino acids and 90 g carbohydrate per day for 28 days. Urine was collected for n-telopeptide (NTX), deoxypyridinoline (DPD), calcium, and pH determinations. Bone mineral content was determined and potential renal acid load was calculated. Bone-specific alkaline phosphatase was measured in serum samples collected on day 1 (immediately before bed rest) and on day 28. Potential renal acid load was higher in the AA group than in the Con group during bed rest (P < 0.05). For all subjects, during bed rest urinary NTX and DPD concentrations were greater than pre-bed rest levels (P < 0.05). Urinary NTX and DPD tended to be higher in the AA group (P = 0.073 and P = 0.056, respectively). During bed rest, urinary calcium was greater than baseline levels (P < 0.05) in the AA group but not the Con group. Total bone mineral content was lower after bed rest than before bed rest in the AA group but not the Con group (P < 0.05). During bed rest, urinary pH decreased (P < 0.05), and it was lower in the AA group than the Con group. These data suggest that bone resorption increased, without changes in bone formation, in the AA group.

bone resorption; methionine; n-telopeptide; acidosis; bed rest


Address for reprint requests and other correspondence: S. M. Smith, Nutritional Biochemistry Laboratory, Human Adaptation and Countermeasures Office, Mail Code SK3, NASA Johnson Space Center, Houston, TX 77058 (E-mail: scott.m.smith{at}nasa.gov)




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