NASA's "Twins Study," comparing effects on the human body after almost a year in space by measuring the physiological and cognitive changes in the twins — one who spent 340 days in space and another who remained on earth — was published Friday in the journal Science, with promising results.
NASA collected and analyzed over 300 blood, urine and stool samples from astronaut Scott Kelly, who spent almost a year in space between 2015-2016, even as his retired astronaut twin brother, Mark, stayed back home on earth.
"The space environment is made harsh and challenging by multiple factors, including confinement, isolation, and exposure to environmental stressors such as microgravity, radiation, and noise," the study's abstract notes.
"The selection of one of a pair of monozygotic (identical) twin astronauts for NASA's first one year mission enabled us to compare the impact of the spaceflight environment on one twin to the simultaneous impact of the Earth environment on a genetically matched subject," the abstract adds.
The study found that while in space, brother Scott's immune system was heightened and his genes were activated in unique ways. Some of the changes in gene expression related to bone formation or repairing DNA were expected, as bone density decreases in space and radiation is known to damage DNA.
Changes to mitochondrial and immune system genes, which affect how the body produces energy and how well its protected, however, came as a surprise, although the brothers' epigenomes — chemical compounds and proteins that can attach to DNA and turn certain genes on or off — revealed a less than 5-percent difference.
Scott experienced changes in body mass and a swelling of blood vessels, thickening of the carotid artery, as well as changes in the shape of his eyes and alterations to his microbiome. His cognitive speed and accuracy were also shown to have decreased while he was in space.
However, some six months after returning to earth, Scott's bodily and mental functions returned to normal, although seven percent of the gene expression related to his immune system and DNA repair did not completely return to pre-flight levels.
"As soon as [Scott] got into space, there was a large-scale shift in over 1,000 genes that are actually dynamically changing […] so, clearly the body and cells were adapting," Christopher Mason, a geneticist at Weill Cornell Medical Center in New York and co-author on the study, said during a press conference last week.
"We saw enrichment — the kinds of genes that were becoming activated include things that regulate DNA damage response, activate DNA repair [and] maintain telomere lengths […] and also, most notably, the most enriched set of genes [were] almost all involved in the immune system regulation, which indicated to us that the immune system is almost on a high alert as a way to try and understand this new environment," Mason added.
In addition, researchers noted that Scott's telomeres — which protect the ends of chromosomes from deterioration — grew longer in space, despite the fact that telomeres are known to get shorter with age.
"Telomeres [are] the ends of our chromosomes that shorten as we get older," Susan Bailey, co-author of the study, said during the press conference last week.
"They can serve as a biomarker of accelerated aging or some of the associated health risks, like cardiovascular disease or cancer. So, certainly we imagined, going into the study, that the unique kinds of stresses and extreme environmental exposures like space radiation and microgravity, all of these things, would act to accelerate telomere loss," Bailey said.
"I don't think that [the elongation] can really be viewed as the fountain of youth and that people might expect to live longer because they're in space," she added, addressing the fact that Scott's telomeres grew older with age.
Researchers subsequently noted that Scott's telomeres became shorter after he returned to earth.
NASA researchers expressed hope about the study's findings.
"The bottom line is, from all these studies — and, granted, this is an experiment with one data point […] would be that there's nothing that we saw that would prevent us from going to Mars," Scott recently told Space.com.
"Certainly, there's some stuff that they're going to continue to look at — gene expression, telomeres, other issues astronauts have with their vision, but no showstoppers that jumped out at anyone," the astronaut added.