Nutritional countermeasures for spaceflight-related stress

Optimal function of the immune system requires nominal, if not optimal, nutritional status. This fact led to the concept of “Immunonutrition” which describes diets that are specifically designed to enhance immune system function. Without adequate nutrition, the immune system is deprived of critical components needed to generate an effective immune response. In many cases, nutrients act as either (or both) antioxidants and enzyme cofactors. It is well known from terrestrial research that insufficiency or deficiency of macronutrients or certain micronutrients (e.g., zinc, selenium, and antioxidant vitamins) can have profound effects on immune function. It leads also to a dysregulation of the balanced host response. Crews during spaceflight have historically had lower dietary intake compared with normal conditions on ground, which could very well contribute to altered immune system function. Altered nutritional status and/or insufficient/inappropriate dietary intake of astronauts during spaceflight might influence host immune responses and resistance to infection, especially given the increased stress associated with spaceflight. Some of the immune function alterations documented in astronauts in this volume have been reported in states of nutrient deficiencies. At a minimum, maintenance of dietary intake could potentially counteract the immune alterations, and ideally, optimized nutrition and nutrient intake may improve immune responsiveness. A clear understanding of nutrition (e.g., absorption, metabolism, and excretion of micronutrients) and other newly discovered thermoregulatory function during spaceflight is required before specific nutritional recommendations can be made, especially with regard to their relationship with optimizing immune system function.