cal activity undertaken by the crew and by space flight itself. Smith and Heer (2002) pointed to the need to ensure adequate dietary intake (and synthesis, when applicable) of various nutrients involved in bone and calcium homeostasis, including calcium, vitamins D and K, protein, sodium, and phosphorus. Similarly, homeostasis of red and white blood cells, as well as vascular integrity, bone mass, and osmolality, may be altered by the quality of nutrition (Smith et al., 2005), whereas crew morale can be affected by the appearance and quality of food (Kerwin and Seddon, 2002). In addition, adequate quantity and quality of water must be ensured.
Despite the efforts by NASA’s nutrition and food scientists, there is evidence that astronauts have had energy intakes 30 percent to 40 percent lower than their needs during space missions (Smith and Lane, 1999), not because of faulty planning in terms of nutrient intake or unbalanced menus, but because of such factors as time constraints (e.g., time for meal preparation and consumption), work overload, and lack of appetite. Moreover, it is well established that astronauts’ energy expenditures in space are unchanged or even increased from those on Earth (Lane et al., 1997; Stein et al., 1999).
According to Smith et al. (2005), several changes in nutritional status after space flight have been observed. In addition to insufficient energy intake, vitamin D levels were altered after long-duration missions (4 to 6 months), even when the vitamin was taken as a supplement during flight. Further, there was evidence that the metabolism of this vitamin may have been affected by the long-term stay of cosmonauts in the Mir station. Altered vitamin D status, in turn, was associated with increased bone resorption after landing. The same authors reported severe decreases of up to 45 percent for magnesium and phosphorus concentrations. The former may be of concern in long-term missions because of the role of magnesium in preventing formation of renal stones (Su et al., 1991).
Other vitamin levels are also affected by prolonged human exposure to the space environment. The level of vitamin K, an important element in maintaining bone health, was reported to decrease during space flight, and levels of vitamin E and folate may have decreased also (Smith et al., 2005). According to Smith et al., it is not known whether the observed decrease in folate—attributed to inadequate food intake, not to food processing techniques—would be accentuated during prolonged space missions. A review by Lucock (2000) suggests that the role of this B vitamin in maintaining good health may extend beyond prenatal conditioning and a positive influence on cardiovascular disease, to encompass several types of cancer, dementia, and affective disorders.