The NASA Twins Study: Understanding the Impact of Long-Duration Spaceflight on the Human Body

The NASA Twins Study represents a groundbreaking investigation into the effects of long-duration spaceflight on the human body. By comparing the physiological, molecular, and cognitive responses of astronaut twins during a year-long space mission, this study provides valuable insights that can shape future space exploration and ensure the well-being of astronauts on extended missions. The results highlight both transient and persistent changes across various cellular, genetic, and physiological levels, paving the way for the development of countermeasures to mitigate potential risks during prolonged space travel.

Physiological Processes Influenced by Spaceflight:

The study identifies ten key physiological processes that are influenced by long-duration spaceflight. These processes serve as targets for the development of interventions to safeguard the health of astronauts during future exploration-class missions. The processes include body mass and nutrition, telomere length regulation, maintenance of genome stability, vascular health, ocular structural adaptations, transcriptional and metabolic changes, epigenetic shifts, lipid level alterations, microbiome responses, and cognitive function. These associations are categorized into low, medium/unknown, and high-risk groups based on their functional importance and persistence after returning to Earth.

Low-Risk Associations:

Many physiological and molecular changes observed during spaceflight returned to near preflight levels after the mission. These changes included average telomere length, body mass, microbiome composition, T-cell function, and cellular and tissue regulation. These findings suggest that these factors represent important biomarkers for adaptation to space but pose minimal risks for long-duration missions.

Gene Function:

The majority of genes that changed expression during spaceflight returned to normal ranges within six months postflight. The observed changes in metabolic levels and immune stress did not impair immune functions. These results indicate the plasticity and resilience of core genetic, epigenetic, transcriptional, cellular, and biological functions during space travel.

Telomere Elongation:

The study observed telomere elongation during spaceflight, which is consistent with previous findings in astronauts on shorter missions. The underlying mechanisms and consequences of this transient elongation are still unknown. However, lifestyle factors such as metabolic and nutritional status, physical activity, and weight loss have been associated with longer telomeres. The study suggests a correlation between reduced body mass and increased serum folate levels with telomere lengthening.

Microbiome Changes:

The gastrointestinal (GI) microbiome undergoes dynamic changes during spaceflight, likely influenced by diet and other factors. Although each subject maintained individual microbiome characteristics, more changes in microbial community composition and function were observed during the flight period. The inflight changes in microbiome diversity and small-molecule metabolites suggest functional adaptations to spaceflight. However, the health risks associated with these changes are not yet known but are expected to be minimal.

Mid-Level or Unknown Risk Associations:

Collagen regulation, intravascular fluid management, and persistent telomere loss and/or critical shortening represent mid-level or unknown risks associated with long-duration spaceflight. These factors require further investigation to understand their long-term implications and potential health risks for astronauts.

High-Risk Associations:

Returning to Earth after spaceflight poses significant physiological challenges and stress. The study highlights the spaceflight-associated neuro-ocular syndrome (SANS) as a potentially high-risk association. This syndrome, characterized by ocular issues such as optic disc edema and hyperopic shifts, affects around 40% of astronauts. The study suggests that cephalad fluid shift and vascular engorgement may contribute to these ocular changes. The observations underscore the importance of monitoring ocular health and potential long-term consequences for astronauts.

The NASA Twins Study provides a comprehensive understanding of the biomedical responses of the human body during long-duration spaceflight. The findings offer valuable insights into the physiological, molecular, and cognitive changes that occur in astronauts. By identifying key processes influenced by spaceflight, this study lays the foundation for developing effective countermeasures to mitigate potential risks during future exploration-class missions. The study also highlights the need for continued research into mid-level and high-risk associations to ensure the well-being of astronauts during and after space travel.

Sources

1. Science, vol. 364, no. 6436, The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight, Dr. Francine Garrett-Bakelman