Food systems for long-term spaceflight: Understanding the role of non-nutrient polyphenols in astronauts' health.

Background: Manned space exploration missions have developed at a rapid pace, with missions to Mars likely to be in excess of 1000 days being planned for the next 20 years. As such, it is important to understand and address the challenges that astronauts face, such as higher radiation exposure, altered gravity, and isolation. Meanwhile, until now the formulation of space food systems has not focused on non-nutrients, and has not considered issues arising from their absence during space missions or the possibility of them to solve the challenges caused by space hazards. Aims: This study investigates, by systematic review, current space food systems and the potential for non-nutrients, such as flavonoids and polyphenols, to counteract radiation- and low gravity-induced degeneration of bone, vision, muscle strength, immune function and cognition. Results and discussion: A systematic approach found 39 related animal model studies, and that polyphenol dietary interventions have been shown to mitigate radiation-related physiological problems and cognitive decline, as well as reduce the implications of radiotherapy. From the results of these studies, it appears that berry extracts have a significant effect on preventing cognitive problems through attenuating the expression of NADPH-oxidoreductase-2 (NOX2) and cycloocygenase-2 (COX2) in both frontal cortex and hippocampus and immune system problems caused by radiation similar to that experienced in space. For physiological problems like alteration of blood-testicular barrier permeability and oxidative stress in kidney and liver caused by gamma rays and X-rays, various polyphenol compounds including resveratrol and tea polyphenols have a certain degree of protective effect like enhancing metabolism of heart and decreasing DNA damage respectively. Due to the lack of quantitative studies and the limited number of relevant studies, it is impossible to compare which polyphenol compounds are more effective. Only one study showed no difference in the performances of a blueberry extract-fed group and a control group exposed to Fe irradiation after 12 months. Conclusion: In conclusion, current animal studies have shown that polyphenols can mitigate radiation damage to some extent, but more research is needed to enable the application of a polyphenol diet to actual space flights.