Given that long duration space missions (>300 days) are currently rare, and that planned missions to Mars are in the planning stages by public and private entities over the next 20 years, researchers sought to examine the effects of space exposure on the human body over a one-year duration using a pair of monozygotic twin astronauts, Scott and Mark Kelly, who were 50-years-old at the initiation of the study.
Comprised of 84 scientists who made up 10 teams from 12 universities in eight states, researchers of the study evaluated the Kelly twins over 340 days, with Scott living onboard the International Space Station (ISS), while his brother, Mark, remaining on Earth, allowing researchers to juxtapose the impact of the spaceflight environment on one twin with the concurrent impact of the Earth’s environment on genetically matched subjects. Physiological, telomeric, transcriptomic, epigenetic, proteomic, metabolic, immune, microbiomic, cardiovascular, vision-related, and cognitive data were all aggregated and analyzed over a 25 months, spanning three time periods: before (preflight), during (inflight), and after spaceflight (postflight), using an integrated sampling scheme. The research team allowed for a four-year gap between the end of Scott Taylor’s one-year mission in space and the start of the study.
Changes Returned to Baseline
The results of study suggest that some biological functions in Scott were minimally affected by spaceflight and included immune response the first test of influenza (flu) vaccination administered inflight. Although significant changes were found in association with the spaceflight period, including telomere length, gene regulation, gut microbiome composition, body weight, carotid artery dimensions, and retinal thickness, most these changes returned to normal upon Scott’s return to Earth from the ISS.
Considering most of the biological and human variables remained either stable or returned to baseline, the researchers wrote that the data suggest “that human health can be mostly sustained over this duration of spaceflight,” and that the changes described in this study “highlight pathways and mechanisms that may be vulnerable to spaceflight and may require safeguards for longer space missions.”
The results show “the resilience and robustness of the human body,” according to study coordinator Steven Platts, deputy chief scientist for NASA’s Human Research Program, in a CNN article on the study. “When we go into space and experience microgravity and travel at speeds like 17,500 miles an hour, our bodies adapt and continue to function and, by and large, function extremely well.”
Stefan Green, director of the Sequencing Core at the University of Illinois at Chicago, which focused on assessing any changes in the twins’ gut microbiomes, said in a press release that “the overall small and transient effect of extended spaceflight on the gut microbiome we saw in Scott is very promising and suggests that microbial diversity and function can be maintained on even longer flights.”
Green was careful to highlight the small sample size (two individuals) as a limitation of the study and noted that future research would be required to expand upon the findings.
The findings may contain important implications on Earth, as they exhibit how a healthy body adapts to stress, providing potential insight into how the body responds to other stressors, infections, or even cancer (considering that patients fighting cancer undergo genetic changes as well as exposure from radiation treatment). Moreover, the study highlighted how the body responds to flu vaccines, environment-related changes in gene expression, ailments associated with intracranial pressure, visual system impairments, and cardiovascular diseases such as atherosclerosis.
“The science that we do in space impacts our nation for generations,” Mark Kelly said.
Human health can be 'mostly sustained' for a year in space, NASA Twins Study concludes https://t.co/65DBntExX2
— WAMS, The World Academy of Medical Sciences (@WAMSOnline) April 13, 2019
— Microbiome and You (@microbiome) April 19, 2019
Photo by Robert MARKOWITZ / NASA / AFP