Aviation, Space, and Environmental Medicine x Vol. 80, No. 5, Section II x May 2009 A15 Z WART SR, O LIVER SAM, F ESPERMAN JV, K ALA G, K RAUHS J, E RICSON K, S MITH SM. Nutritional status assessment before, during, and after long-duration head-down bed rest. Aviat Space Environ Med 2009; 80(5,Suppl.):A15–22. Introduction: Bed rest is a valuable ground-based model for many of the physiological changes that are associated with spaceflight. Nutri- tional changes during and after 60 or 90 d of head-down bed rest were evaluated. Methods: A total of 13 subjects (8 men, 5 women; ages 26– 54 yr) participated in either 60 or 90 d of bed rest. Blood and urine were collected twice before bed rest and about once per month during bed rest. Samples were stored frozen and batch analyzed. Data were ana- lyzed using repeated-measures analysis of variance. Results: During bed rest, markers of bone resorption (such as N-telopeptide excretion, P , 0.001) increased and serum concentration of parathyroid hormone de- creased ( P , 0.001). Also, oxidative damage markers such as superoxide dismutase increased ( P , 0.05), and after 90 d of bed rest, total antioxi- dant capacity decreased ( P , 0.05). During bed rest, iron status indices showed patterns of increased iron stores with a decreased concentration of transferrin receptors ( P , 0.01). Discussion: These changes are similar to some of those observed during spaceflight, and further document the utility of bed rest as a model of spaceflight. Keywords: spaceflight, nutrition, weightlessness, bone resorption, para- thyroid hormone, oxidative stress, antioxidants, iron, transferrin. S OME OF THE CLINICAL concerns for long-duration spaceflight (longer than 30 d) are bone and muscle loss, inadequate dietary intake, decreased nutrient stores, increased oxidative damage due to factors such as ra- diation exposure and increased iron stores, and altered nutrient metabolism (41). Designing and testing counter- measures to mitigate these negative physiological effects of spaceflight require a solid understanding of changes in nutrient status during spaceflight, because macro- and micronutrients are essential for every cell and function in the body. Data from 11 International Space Station (ISS) astronauts suggest that their nutritional status is compro- mised after long-duration spaceflight (40). Some of the most striking changes are decrements in vitamin D, folate, vitamin K, and vitamin E status, and increases in markers of bone resorption and oxidative damage. Changes in uri- nary excretion of phosphorus and magnesium were also evident after 4 to 6 mo of spaceflight (40). That vitamin D status is decreased after long-duration spaceflight is clearly indicated by results of studies from Skylab, Mir, and ISS missions (17,33,39,40). Even for crewmembers who used supplements, 25-hydroxyvitamin D status decreased (17,40). The low levels of vitamin D in the space food supply and the absence of ultraviolet light during spaceflight likely contribute to this phe- nomenon. Altered vitamin D status is accompanied by evidence of increased bone resorption during and after spaceflight (31,33,40). During spaceflight, the excretion rates of urinary markers of bone resorption are typically 100–150% of their preflight values (3,5,31,33,39). Loss of bone mineral is increased by skeletal unloading during weightlessness (10,21,33,36,39,41). Evidence exists that during and after spaceflight, along with changes in nutrient status, the metabolism of cer- tain nutrients is altered (41), and iron is one of these nu- trients. The data suggest that as a result of microgravity, storage pools of iron are shifted so that less iron is in red blood cells and more is stored in ferritin, and less iron is transported (less transferrin) (35,40). Serum ferritin con- centration is significantly increased, the amount of ferri- tin iron is slightly greater than before launch, and the amount of transferrin is decreased. Red blood cell mass also decreases (1,6,14,43). After landing, a delay in re- placing red blood cells often leads to decreased hemoglo- bin, hematocrit, and mean corpuscular volume (34,40). Like other physiological effects of weightlessness, changes in nutrient status and metabolism can be stud- ied in the bed rest analog of weightlessness. The qualita- tive effects of bed rest on bone and calcium homeostasis are similar to the effects of spaceflight, but the quantita- tive effects are generally less than (about half) those of spaceflight (41). As reviewed by Meck and colleagues (23) and others (25), bed rest is a good model for space- flight, but lack of standard procedures has limited the ability to draw conclusions across studies. This report is one of a series of reports on the Flight Analogs Project, which is designed to lay the groundwork for a standard bed rest protocol. Standard procedures were developed From the Nutritional Biochemistry Laboratory, Human Adaptation and Countermeasures Division, NASA Johnson Space Center, Houston, TX; Enterprise Advisory Services, Inc., Houston, TX; Wyle, Houston, TX; Indiana University-Purdue University, Fort Wayne, IN; and Universities Space Research Association, Houston, TX. Address reprint requests to: Scott M. Smith, Ph.D., NASA Johnson Space Center, Mail Code SK, 2101 NASA Parkway, Houston, TX 77058; scott.m.smith@nasa.gov. Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. DOI: 10.3357/ASEM.BR07.2009 Nutritional Status Assessment Before, During, and After Long-Duration Head-Down Bed Rest Sara R. Zwart, Susan A. Mathews Oliver, J. Vernell Fesperman, Geeta Kala, Jane Krauhs, Karen Ericson, and Scott M. Smith