Long-duration missions are expected to take humans to Mars and beyond during the next decade. We know that the impacts of the spaceflight environment on human health and performance, physiology, and cellular and molecular processes are numerous, because 559 humans have flown into space since 1961. However, only 8 missions have been long duration (>300 days). Therefore, we need more studies to assess the impact of long-duration spaceflights.

Now, the published results of NASA’s Twins Study reveal “some interesting, surprising and positively assuring data” of how a single human body adapted to the extreme environment of space.

To understand the health impact of long-duration spaceflight, one identical twin astronaut was monitored before, during, and after a 1-year mission onboard the International Space Station; his twin served as a genetically matched ground control. Longitudinal assessments identified spaceflight-specific changes, including decreased body mass, telomere elongation, genome instability, carotid artery distension and increased intima-media thickness, altered ocular structure, transcriptional and metabolic changes, DNA methylation changes in immune and oxidative stress–related pathways, gastrointestinal microbiota alterations, and some cognitive decline postflight. Although average telomere length, global gene expression, and microbiome changes returned to near preflight levels within 6 months after return to Earth, increased numbers of short telomeres were observed and expression of some genes was still disrupted. These multiomic, molecular, physiological, and behavioral datasets provide a valuable roadmap of the putative health risks for future human spaceflight.

Garrett-Bakelman, Francine E., et al. ‘The NASA Twins Study: A Multidimensional Analysis of a Year-Long Human Spaceflight’. Science, vol. 364, no. 6436, Apr. 2019, p. eaau8650. science.sciencemag.org, doi:10.1126/science.aau8650.