Prolonged Effects of Physiological Change, Psycho-Social Stress, Zero Gravity, Alterations in the Intestinal Microbiome, and Metabolism on the Response to Space Irradiation

Adaptation to continuous radiation exposure affects not only tissues and organs in the human body but also the components of the human microbiome (bacteria, fungi, and viruses) in the intestine, lung, and skin, and their interaction with each other and human tissues over time. Physiological and metabolic changes also result from continuous radiation exposure and are also associated with increased levels of measurable changes in human cellular DNA. A major area of research is whether these changes are associated with deleterious effects on astronauts including lowering the susceptibility of humans to opportunistic infections, and rapid aging. Alternatively, the detected changes may not be associated with deleterious effects but may actually indicate the capacity of humans to adapt to this new altered baseline of higher levels of ionizing irradiation exposure. The controversy has led to new areas of research.