NASA Twins Study Provides New Insight Into How Space Travel Affects Human Health

Thanks to 18 years of humans continuously working on the
International Space Station (ISS), we already have a basic idea of
what happens to our Earth-grown bodies in zero gravity. Our hearts
morph in shape, lowering the amount of oxygen the blood can absorb
and carry. Our bones and muscles wither without gravitational
challenge. Fluids rush towards our heads, increasing pressure in
the eyes.

Many of these symptoms seem to worsen the longer humans remain
in space. Yet with space missions often only lasting six months,
how our bodies and minds adapt to
long-term space flight
—that is, if we can at all—remains a
complete mystery.

Until now. This week, an ambitious collaboration organized by
NASA of over 80 scientists across ten teams published
the most comprehensive study yet of what happens to humans in
space—and upon return to our pale blue dot.

The news is good. Overall, the data “demonstrated on the
molecular level the resilience and robustness of how one human body
adapted to the spaceflight environment,” said Dr. Jenn Fogarty,
chief scientist of the NASA Human Research Program. “This study
was a stepping stone to future biological space research focusing
on molecular changes and how they may predict health and
performance of astronauts.”

Landmark Effort

The actual results aren’t even the most impressive parts of
the study. Rather, the technical tour-de-force stands out in its
sheer scope and study subjects.

For 25 months, the teams examined astronauts before, during, and
after a year of spaceflight. By analyzing multiple time points,
they were able to construct stop-motion “movies” that track
changes in their biology over time in exquisite detail. The results
span nearly the entire spectrum of biomedicine: at the micro-level,
from gene expression, DNA damage, and cellular metabolism to
changes in the microbiome and immune system; at the macro-level,
shifts in cognition, body weight, eyesight, and cardiovascular
functions.

It marks the first time NASA examined multiple layers of
biological data, or “multi-omics” for space travel.

But perhaps more unique were the study subjects:
astronauts Scott and Mark Kelly
, a pair of identical twins.
Although Mark had previously spent short bouts in space, he
remained on Earth for the duration of this study—aptly named the
NASA Twin Study—while Scott spent 340 days on the ISS. Because
the astronauts share the same basic genetic blueprint,
“nature,” scientists had an exceptional opportunity to tease
out the effect of “nurture”—space travel.

The caveat is that the results and conclusions may not entirely
hold for others. “We really can’t say if any of the results are
due to space travel or coincidence,” the team acknowledged.
However, their data does indicate areas to focus on in future
studies involving other astronauts, which could eventually allow
them to understand and counteract the negative health effects of
space, they said.

With commercial spaceflight ramping up, a return to the moon in
the works, and a three-year venture to Mars within sight, we’re
eagerly scattering into the final frontier. Guided by the Twin
Study, these future projects will offer new opportunities to
further “contextualize” our physiology in long-term
spaceflight, the authors said.

Limited Changes in Store

When it comes to specific bodily changes the conclusions get
murkier.

First, the genes. Radiation is a known trigger for DNA damage,
and the teams found extensive changes in Scott’s DNA
expression—how his genes make proteins—compared to his
brother.

Some of the changes were expected: those involved in bone repair
and DNA repair, for example, which kept up even after Scott
returned to Earth, suggesting his genome was relatively unstable.
The teams also found changes in his mitochondrial genes, which
could control how cells generate energy, as well as several genes
related to his immune system . Whether those genetic changes
actually affected his immune system is unclear; a flu vaccine given
to Scott in space worked as intended.

“Gene expression changed dramatically,” said Mason, whose
team worked on genomics. “In the last six months of the mission,
there were six times more changes in gene expression than in the
first half of the mission.”

However, over 91 percent of expression changes reverted back to
baseline for Scott within six months after he returned home.
“Overall, these data show plasticity and resilience for many core
genetic…and biological functions,” the team concluded.

Dr. Andrew Feinberg and Dr. Lindsay Rizzardi explains why studying
twin astronauts helps tease out health factors related to
spaceflight. Credit: Johns Hopkins Medicine

More startling were Scott’s telomeres, the “end caps” that
protect chromosomes when they replicate. The guardians of the
genome, telomeres are known to shorten with age, which could
explain why our genome becomes more unstable as we age. Shockingly,
Scott’s telomeres became longer in space—generally considered a
protective response.

“We were surprised, that was the first reaction,”
said 
Dr. Susan Bailey at Colorado State University, who led
the study.

Susan Bailey explains her findings about telomere changes in space
and upon returning to Earth. Credit: Colorado State University.

However, within months of returning, the team found more
“frayed” chromosome ends, suggesting that some of Scott’s
telomeres had disintegrated to the point of complete loss. The
health effects aren’t immediately clear; short telomeres
correlate with age-related diseases such as heart disease and
cancer, for example, but whether Scott is now at higher risk for
these health problems remains anyone’s guess. Nevertheless,
telomere shortening is a clear field for scientists to keep
exploring.

Second, the body. Similar to previous cases, Scott had problems
with his eyes due to fluid buildup, and some of the issues remained
even coming home, whereas his Earth-bound brother experienced no
eye problems during the study. In flight, Scott’s cardiovascular
system also suffered, resulting in “puffy face” syndrome, and
his immune system ramped up, suggesting that his body was under a
state of stress. His kidney function also changed in a way to could
lead to dehydration and kidney stones, although he didn’t have
any issues.

Finally, when subjected to a battery of cognitive tests, Scott
performed worse in nearly all of them except for spatial
orientation after his space flight, and both his speed and accuracy
of reasoning seemed to suffer for at least half a year upon
returning home. Scientists aren’t quite sure if space is to
blame: the trauma of re-entering Earth and the demand for
astronauts to participate in research studies and media events
could have taxed his mental reservoir during the exam, resulting in
poor performance.

Above and Beyond

The Twin Study, although remarkable, is only the beginning.

To gather data in space, the teams developed a bank of new
tools, such as a portable DNA sequencing technique that works
aboard the ISS. Although not used in this study, the sequencer
could eventually allow astronauts to “read” their own DNA in
microgravity during longer spaceflights without relying on home
command.

And looking ahead, a year in space isn’t that long. A round
trip to Mars is projected to last three years, during which
astronauts would be exposed to even more radiation as they travel
beyond the protection of Earth’s magnetic field. We’ll need
more studies examining the health impact of even longer spaceflight
in the future.

But this effort is a foundation-building start.

“Undoubtedly, the study…represents more than one small step
for mankind in this endeavor,” concluded Löbrich.

Image Credit:
Andrey Armyagov
/ Shutterstock.com

Source: *FS – All – Science News 2 Net
NASA Twins Study Provides New Insight Into How Space Travel Affects Human Health