NASA twins study finds no red flags for long-term space travel

Physiological and genetic effects of life on the ISS return to pre-flight levels soon after return to Earth. Nick Carne reports.

Scott Kelly outside the International Space Station during a spacewalk. 

NASA via Getty Images

So, what does a year in space do to the human body? Quite a lot in total, but nothing too drastic overall is the short, non-scientific answer.

NASA, of course, will be trying to mine something a little more scientific and detailed from the findings of its unique Twins Study, just released.

A large team of researchers spent 25 months tracking the physical state of astronaut Scott Kelly before, during and after his near one-year stint on the International Space Station (ISS) and comparing him with his twin brother Mike, an astronaut who remained on Earth as a ground control.

Biological samples obtained while Scott was in orbit were either frozen and later shipped, or immediately returned to Earth via Soyuz resupply rockets for processing.

Combining biological analysis with physiological and cognitive tests, NASA’s team, led by Francine Garrett-Bakelman from Weill Cornell Medicine in New York, found no significant health differences between the brothers, but several changes of note in Scott, some of which persisted beyond his time in orbit.

Astronaut Scott Kelly and his twin brother Mike.


These included a small (less than 5%) difference in DNA methylation, which plays a role in gene regulation, and temporary changes in the expression of some of his genes, especially those related to the immune system.

Changes to the shape of his eyeball, including a thicker retinal nerve, also were reported, as well as a decline in some cognitive abilities as measured by a series of tests.

However, these changes cannot be attributed to space flight alone, the researchers stress.

“Our results demonstrate both transient and persistent changes associated with long-duration spaceflight across multiple cell types, tissues, genotypes, and phenotypes,” they write in a paper published in the journal Science.

“These specific data, as well as the broader biomedical measures and sample collection methods, can now serve as a foundation for scientific and medical assessments of future astronauts, especially for those on prolonged, exploration-class missions.”

Such as going to Mars, for example.

As human biologists Markus Löbrich and Penny Jeggo note in a commentary in the same journal, the study was run “over the expected time frame needed to reach Mars, providing an unprecedented source of information”.

“The challenges encountered in space include noise, isolation, hypoxia, and disrupted circadian rhythm (body clock),” they write.

“Furthermore, exposure to ionising radiation (IR) and weightlessness, also called microgravity, could cause important health risks.”

Garrett-Bakelman and colleagues classified the effects they observed in Scott as low, medium or high. The low-risk category included changes in the gastrointestinal microbiome and in body mass, and the mid-level risk category involved such things as alterations in collagen regulation and intravascular fluid management.

Genomic instability, assessed by chromosomal aberrations, was placed into the potentially higher-risk group because it confers a risk of developing cancer.

“These risk classifications are made on the basis of the degree of potential functional importance during spaceflight and their persistence for at least six months after returning to Earth,” the authors write.

They report that many rapid physiological and molecular changes associated with spaceflight returned to near pre-flight levels, including average telomere length, body mass, microbiome composition, T-cell function and most cellular and tissue regulation.

“Owing to their pronounced responses during spaceflight, these serve as important potential biomarkers for adaptation of the human body in space but likely represent minimal to low risks for long-duration missions,” the add.

The authors note that their study must be considered only “as hypothesis-generating and framework-defining”, but that does not diminish its importance if space travel is to become much more common and much more demanding.

As they say, the understanding of the physiological and functional consequences of space missions of up to six months has increased greatly over the 18 years of continuous human presence on the ISS, but there is virtually no experience of longer periods in orbit. Only four people have undertaken missions of a year or longer.

“Genetic, immune system, and metabolic functions are of particular concern given exposure to space radiations, restricted diet, reduced physical work requirements, disrupted circadian rhythms, and weightlessness,” they write.

“Importantly, longitudinal measures of biomarkers (such as genomic, epigenomic, biochemical, and physiological alterations) can provide critical metrics for astronaut health that could aid in assessment of increased risks and guide potential personalised interventions.”

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