“The Twins Study gave us a first sketch of the human body’s molecular responses to spaceflight, but these outlines needed to be filled in,” says Christopher Mason, an associate professor of physiology and biophysics at Weill Cornell Medicine. “The changes we saw needed more context and replication. We needed additional studies to map out the frequency of the changes we observed in other astronauts, and other organisms, that go into space, and also to see if the degree of change was similar for shorter missions.”
That brings us to a new package of research that builds on the Twins Study, reanalyzing some of the original data with new techniques and providing comparisons with other astronauts. In a set of 19 studies published today in a slew of different journals (along with 10 preprints still under peer review), researchers like Mason (a senior author on several of the papers) studied the physiological, biochemical, and genetic changes that occurred in 56 astronauts (including Kelly) who have spent time in space—the largest study of its kind ever conducted.
The new papers, which incorporate results from cell-profiling and gene-sequencing techniques that have become easier to run only recently, reveal that “there are some features of spaceflight that consistently appear in humans, mice, and other animals when they go to space,” says Mason. “There appears to be a core mammalian set of adaptations and responses to the rigors of spaceflight.”
The researchers highlight six biological changes that occur in all astronauts during spaceflight: oxidative stress (an excessive accumulation of free radicals in the body’s cells), DNA damage, dysfunction of the mitochondria, changes in gene regulation, alterations in the length of telomeres (the ends of chromosomes, which shorten with age), and changes in the gut microbiome.
Of these six changes, the most surprising one for scientists was mitochondrial dysfunction. Mitochondria play a critical role in producing the chemical energy necessary to keep cells—and by extension, tissue and organs—functional. Irregular mitochondrial performance was found in dozens of astronauts, and it would help explain why so many astronauts have reported immune system problems, issues with the function of organs like the liver and heart, and disrupted circadian rhythms.
Other research homed in on problems observed at the genetic level. The Twins Study showed that Kelly’s telomeres got longer in space before shrinking back to normal or even shorter lengths soon after he returned to Earth. Telomeres are supposed to shorten with age, so lengthening makes little sense, and the Twins Study didn’t provide enough data to prompt any real conclusions as to why it happened and what the effects were.
Susan Bailey, a Colorado State University expert on telomere research and a senior author for several of the papers, says the new research found that 10 other astronauts experienced the same telomere lengthening Kelly did irrespective of mission duration—as well as the same telomere shrinking once they came back to Earth.
Notably, one of the papers in the new package found that longer telomeres were also associated with