findings show a link between nutrition, genetics and ocular changes during bed
rest, an analog of spaceflight. These findings support and extend earlier
findings in astronauts and may point to potential low-risk countermeasures.
For a decade
now, it has become clear that some astronauts experience ocular changes that can
affect vision during and after International Space Station missions. This is
referred to as Spaceflight Associated Neuro-ocular Syndrome (SANS). One notable
change is optic disc edema—or swelling where the nerve that comes from the
brain connects to the back of the eye. Not all astronauts develop the same
magnitude of SANS and, for example, it is estimated that about one in five
develop optic disc edema. This suggests that there are multiple factors
Biochemistry Lab at NASA’s Johnson Space Center has been studying this for more
than eight years now. They initially identified differences in blood chemistry
of affected astronauts, differences that existed before flight. These chemical differences were metabolites associated
with B-vitamins like folate and vitamin B12. They followed up by examining
genetic variants known as single nucleotide polymorphisms, or SNPs, related to
these biochemical differences and vitamins. They found that genetics and
B-vitamin status were associated with the development of ocular changes in
astronauts. These findings were supported by data in the recent Twins Study
publication in Science.
this team worked with the NASA Cardiovascular and Vision Lab to identify that
these same genetic differences also affected response to an acute carbon
dioxide exposure. Carbon dioxide levels within the space station
are higher than on Earth. Carbon dioxide affects blood vessel function and
blood flow into the head, and thus is a potential contributor to astronaut eye
Bed rest is
often used to simulate aspects of spaceflight. Until recently, these eye
changes had never been seen in bed-rest subjects. A study conducted in Germany
recently exposed subjects to 30 days of strict head-down tilt bed rest with
increased ambient carbon dioxide levels, resulting in some of these subjects
developing optic disc edema. The new publication in JAMA Ophthalmology documents that the magnitude of optic disc edema
was associated with the same genetic variants and B-vitamin status.
In this paper,
the authors also extend their earlier hypothesized mechanism, suggesting that
changes in genetics and vitamin status might affect the chemistry of the
proteins that help the back of the eye maintain its structure, making it
more susceptible to fluid shifts. Scott M. Smith, Ph.D., is a NASA nutritionist
and co-author of the paper noted.
identified an association between genetics, vitamin status and SANS,” Smith
said. “We’ve hypothesized a plausible mechanism. As with all hypotheses, this
needs to be tested experimentally.”
findings could have significant implications for NASA. If these ocular changes
are genetically predisposed, as eight years of research suggests, this could help
refine research and development for countermeasures. Smith said, “Given the
role of B-vitamins in this process, obviously there is potential for vitamin
supplementation to alter the physiology of at-risk astronauts, and thus
mitigate, or even prevent, ocular issues in astronauts.”
the findings could have tremendous implications for terrestrial medicine, where
individuals with these types of genetic differences are prone to cardiovascular
and other health issues.
By daring to
study the complex biochemistry underlying physiology of the eye, and by uniting
scientific teams across disciplines with clinicians, this research may help
enable crew health and safety on exploration-class missions of the future.
Smith and Sara
R. Zwart, Ph.D., lead author of the paper, direct the Nutritional Biochemistry
Laboratory at Johnson.
To view the
paper, click here.
Astronaut Karen Nyberg, Expedition 37 flight engineer, performs an Ocular Health fundoscope exam in the Destiny laboratory of the International Space Station. Image Credit: NASA