by Shaneequa Vereen
NASA Johnson Space Center
HOUSTON — Recent research 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 involved.
The Nutritional 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.
Subsequently, 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 changes.
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.
“We’ve 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.”
Ultimately, these 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.”
Beyond NASA, 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.