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Calcium Kinetics during Bed Rest with Artificial Gravity and Exercise Countermeasures
Author(s) -
Smith Scott M.,
Sceppa Carmen Casteneda,
O'Brien Kimberly O.,
Abrams Steven A.,
Gillman Patti,
Zwart Sara R.,
Wastney Meryl E.
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.233.6
Subject(s) - chemistry , urine , calcium , excretion , zoology , calcium metabolism , medicine , isotopes of calcium , endocrinology , biochemistry , biology , organic chemistry
To assess the potential for artificial gravity (AG) and exercise (EX) to mitigate the effects of bone loss during space flight, we performed two studies: (1) a 21‐d bed rest (BR) with subjects receiving 1 h/d AG (n=8) or no AG (n=7) and (2) a 28‐d BR with 1 h/d 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 d of BR, and blood, urine, and feces were sampled for up to 14 d. Tracers were measured using thermal ionization mass spectrometry. Data were analyzed by compartmental modeling. Ca balance during BR (−316±185 mg/d) and BR+AG (−292±141 mg/d) was lower than before BR because less Ca was absorbed. However, Ca balance did not change with BR+EX, even though absorbed Ca decreased and urinary Ca excretion increased, because endogenous excretion decreased and bone deposition increased. Both studies were designed to restrict energy intake during BR (to maintain body weight in the AG study, and to mimic decreased intake in some astronauts in the exercise study). Ca intake was also decreased during BR (by 215 mg/d in the AG study and 112 mg/d in the EX study), resulting in lower absorbed Ca. We conclude that 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. These studies were funded by NASA and NSBRI.