NASA's Twin Study offered a rare and valuable opportunity to understand the specific impacts of the space environment on the human body through long-term observation of genetically nearly identical monozygotic twins. The study compared Scott Kelly, who spent a year aboard the International Space Station, with his brother Mark Kelly, who remained on Earth. Covering various dimensions including physiological, molecular, cognitive, and biomedical aspects, the research found that spaceflight affects gene expression, immune system function, cardiovascular health, eye structure, and cognitive function, revealing a series of subtle yet significant differences that provide new insights into how spaceflight impacts human health.
During his time in space, Scott experienced significant changes in gene expression, indicating a direct impact of the space environment at the genetic level. These changes spanned aspects from immune responses to DNA repair. While most alterations returned to normal within months after returning to Earth, some gene expression levels showed persistent changes compared to pre-space levels, suggesting that long-term space travel could induce some long-lasting physiological changes.
An unexpected finding in the study was that Scott's telomeres—structures that protect the ends of chromosomes—temporarily lengthened in space. Telomere length is typically associated with the aging process, and this finding thus sparked broad interest in how spaceflight might affect the human aging process. Although this lengthening reversed after Scott returned to Earth, the phenomenon provided significant biological insights, particularly regarding how to manage and maintain astronaut health over the long term in space.
After returning to Earth, Scott showed a slight decline in some cognitive tests, suggesting that the space environment might have short-term effects on cognitive function. These changes could be related to how microgravity affects brain structure and function in space.
Differences in the microbiomes of Scott and Mark suggested that the space environment could affect the balance of microorganisms in the body. Changes in the microbiome are critically important to human health, affecting everything from digestion to the immune system.
Due to the lack of gravity, Scott experienced a shift of body fluids towards his head during his time in space, which could impact vision and other physiological processes. This finding highlights the importance of gravity in the distribution of body fluids and the physiological challenges that need to be overcome during spaceflight.
These differences not only highlight the potential impacts of the space environment on the human body but also provide important insights into how humans can adapt to these extreme conditions. NASA's Twin Study has provided key data and insights for future space exploration, especially for long-duration missions, and has also opened new pathways for improving human health and disease management on Earth.
References:
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Garrett-Bakelman, F. E., Darshi, M., Green, S. J., Gur, R. C., Turek, F. W., et al. (2019). The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight. Science, 364(6436). https://doi.org/10.1126/science.aau8650
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Twins Study - Retrieved from NASA website on April 5, 2024. https://www.nasa.gov/twins-study
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