Nutrition
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Radiation hazards in outer space present an enormous challenge for the biological safety of astronauts. A deleterious effect of radiation is the production of reactive oxygen species, which result in damage to biomolecules (e.g., lipid, protein, amino acids, and DNA). Understanding free radical biology is necessary for designing an optimal nutritional countermeasure against space radiation-induced cytotoxicity. ⋯ There has been growing evidence over the past three decades showing that malnutrition (e.g., dietary deficiencies of protein, selenium, and zinc) or excess of certain nutrients (e.g., iron and vitamin C) gives rise to the oxidation of biomolecules and cell injury. A large body of the literature supports the notion that dietary antioxidants are useful radioprotectors and play an important role in preventing many human diseases (e.g., cancer, atherosclerosis, stroke, rheumatoid arthritis, neurodegeneration, and diabetes). The knowledge of enzymatic and non-enzymatic oxidative defense mechanisms will serve as a guiding principle for establishing the most effective nutrition support to ensure the biological safety of manned space missions.
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To date, several hundred cosmonauts and astronauts have flown in space, yet knowledge about the adaptation of their immune system to space flight is rather limited. It is evident that a variety of immune parameters are changed during and after space flight, but the magnitude and pattern of these changes can differ dramatically between missions and even between crew members on the same mission. A literature search was conducted involving a total of 335 papers published between 1972 and 2002 that dealt with the key words immune response, microgravity and astronauts/cosmonauts, isolation, gravity, and human health. ⋯ That stress plays an important role in the effects of space flight on immunologic parameters is suggested by the frequent findings that stress hormones are upregulated during and after space flight. Unfortunately, however, the existing data on hormonal parameters are almost as varied as those on immunologic changes, and correlations between the two datasets have only rarely been attempted. The functional implications of space flight-induced alterations in immune response largely remain to be elucidated, but the data suggest that long-term travel will be associated with the development of immune-compromised hosts.
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Space flight anemia is a widely recognized phenomenon in astronauts. Reduction in circulating red blood cells and plasma volume results in a 10% to 15% decrement in circulatory volume. ⋯ Iron availability increases, and (in the few subjects studied) iron stores increase during long-duration space flight. The consequences of these changes are not fully understood.
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Conducting research during actual or simulated weightlessness is a challenging endeavor, where even the simplest activities may present significant challenges. This article reviews some of the potential obstacles associated with performing research during space flight and offers brief descriptions of current and previous space research platforms and ground-based analogs, including those for human, animal, and cell-based research. This review is intended to highlight the main issues of space flight research analogs and leave the specifics for each physiologic system for the other papers in this section.
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Space travelers experience a flight duration-dependent loss in weight and body mass while in a microgravity environment, despite the absence of increased energy expenditure. Anorexia in space can lead to in-flight caloric deficits of 1330 kcal per 70 kg astronaut per day in the presence of abundant food and has a critical effect on endurance and performance. Microgravity, alterations in the light-and-dark cycle, and exposure to radiation energy are the environmental stresses believed to influence appetite, food intake, and gastrointestinal function during space flight. ⋯ Modulation of hypothalamic activity, 5-HT, and CRF play a critical role in anorexia related to microgravity and circadian rhythm alterations. Specific gene knockout mice (e.g., 5-HT or CRF and their respective receptors) may prove fruitful in defining the pathways by which anorexia in space occurs. An understanding of these pathophysiologic problems as they relate to appetite, food intake, gastric emptying and gastrointestinal function, sufficiently to derive successful practical solutions, may lead to a quantitative enhancement of physiologic well-being and performance status, serving as a productive countermeasure in space.