Ever since astronauts began going to space for extended periods of time, it has been known that long-term exposure to zero-gravity or microgravity comes with its share of health effects. These include muscle atrophy and loss of bone density, but also extend to other areas of the body leading to diminished organ function, circulation, and even genetic changes.
For this reason, numerous studies have been conducted aboard the International Space Station (ISS) to determine the extent of these effects, and what strategies can be used to mitigate them. According to a new study which recently appeared in the International Journal of Molecular Sciences, a team of NASA and JAXA-funded researchers showed how artificial gravity should be a key component of any future long-term plans in space.
It’s been over forty years since the Apollo Program wrapped up and the last crewed mission to the Moon took place. But in the coming years and decades, multiple space agencies plan to conduct crewed missions to the lunar surface. These includes NASA’s desire to return to the Moon, the ESA’s proposal to create an international Moon village, and the Chinese and Russian plans to send their first astronauts to the Moon.
For this reason, a great deal of research has been dedicated to what the health effects of long-duration missions to the Moon may be – particularly the effects a lower gravity environment would have on the human body. But in a recent study, a team of pharmacologists, geneticists and geoscientists consider how being exposed to lunar dust could have a serious effect on future astronauts’ lungs.
Because it has no atmosphere, the Moon’s surface has been pounded by meteors and micrometeroes for billions of years, which have created a fine layer of surface dust known as regolith. In addition, the Moon’s surface is constantly being bombarded by charged particles from the Sun, which cause the lunar soil to become electrostatically charged and stick to clothing.
Indications that lunar dust could cause health problems first emerged during the Apollo missions. After visiting the Moon, astronauts brought lunar soil back with them into the command module as it clung to their spacesuits. After inhaling the dust, Apollo 17 astronaut Harrison Schmitt described having symptoms akin to hay fever, which including sneezing, watery eyes and a sore throat.
While the symptoms were short-lived, researchers wanted to know what the long-term effects of lunar dust could be. There have also been indications that exposure to lunar dust could be harmful based on research that has shown how breathing dust from volcanic eruptions, dust storms and coal mines can cause bronchitis, wheezing, eye irritation and scarring of lung tissue.
Previous research has also shown that dust can cause damage to cells’ DNA, which can cause mutations and eventually lead to cancer. For these reasons, Caston and her colleagues were well-motivated to see what harmful effects lunar soil could have on the human body. For the sake of their study, the team exposed human lung cells and mouse brain cells to samples of simulated lunar soil.
These simulants were created by using dust samples from Earth that resemble soil found on the Moon’s lunar highlands and volcanic plains, which were then ground to a fine powder. What they found was that up to 90% of human lung cells and mouse neurons died when exposed to the dust samples. The simulants also caused significant DNA damage to mouse neurons, and the human lung cells were so effectively damaged that it was impossible to measure any damage to the cells’ DNA.
The results show that breathing lunar dust (even in minute quantities) could pose a serious health hazard to astronauts traveling to any airless bodies in the future. This includes not only the Moon, but also Mars and other terrestrial bodies like Mercury. Until now, this health hazard has been largely overlooked by space agencies seeking to understand the long-term health risks of space travel.
“There are risks to extraterrestrial exploration, both lunar and beyond, more than just the immediate risks of space itself,” said Rachel Caston. According to Bruce Demple, a biochemist at Stony Brook University School of Medicine and senior author of the new study, their results (coupled with the experience of the Apollo astronauts) indicate that prolonged exposure to lunar dust could impair airway and lung function.
What’s worse, he also indicated that if the dust induces inflammation in the lungs, it could increase the risk of more serious diseases like cancer. “If there are trips back to the Moon that involve stays of weeks, months or even longer, it probably won’t be possible to eliminate that risk completely,” he said.
Ergo, any attempts to mitigate the risks of mounting crewed missions to the Moon, Mars, and beyond will have to take into account exposure to not only low-gravity and radiation, but also electrostatically charged soil. Aside from limiting the duration of missions and the number of EVAs, certain protective counter-measures may need to be incorporated into any plans for long-duration missions.
One possibility is to have astronauts cycle through an airlock that would also spray their suits with water or a compound designed to neutralize the charge, thus washing them clean of dust before they enter the main habitat. Otherwise, astronauts working in the International Lunar Village (or any other off-world habitat for that matter) may have to wear breathing masks the entire time they are not in a spacesuit.
On March 1st, 2016, American astronaut Scott Kelly returned to Earth after spending a total of 340 days aboard the International Space Station (ISS). As part of NASA’s goal to send astronauts on long-duration space flights to Mars and beyond, this record-setting stay in space was designed to test the limit of human endurance in a microgravity environment.
Also known as the Twin Study, this experiment consisted of Kelly spending nearly a year in space while his identical twin (Mark Kelly) remained on Earth. Since Kelly’s return, the two have been subjected to medical tests to see what long-term effects microgravity has had of Scott’s Kelly’s physique. The final results of this test, which were just released, reveal that Scott has experienced changes at the genetic level.
The study was conducted by NASA’s Human Research Program, and the preliminary findings were released at their Investigator’s Workshop on the week of January 23rd, 2017. According to these findings, Scott Kelly showed indications of inflammation, changes in his telomeres and telomerase (parts of the chromosonal system related to aging), a decrease in bone density and gastrointestinal changes – all of which were expected.
As NASA reported in their preliminary findings:
“By measuring large numbers of metabolites, cytokines, and proteins, researchers learned that spaceflight is associated with oxygen deprivation stress, increased inflammation, and dramatic nutrient shifts that affect gene expression… After returning to Earth, Scott started the process of readapting to Earth’s gravity. Most of the biological changes he experienced in space quickly returned to nearly his preflight status. Some changes returned to baseline within hours or days of landing, while a few persisted after six months.”
At the same time, the study took into account possible genomic and cognitive changes between the two brothers. These findings were recently clarified by NASA, which indicated that 93% of Scott Kelly’s genes returned to normal after he returned to Earth while the remaining 7% points were missing. These were attributed to “longer-term changes in genes related to his immune system, DNA repair, bone formation networks, hypoxia, and hypercapnia.”
In other words, in addition to the well-documented effects of microgravity – such as muscle atrophy, bone density loss and loss of eyesight – Scott Kelly also experienced health effect caused by a deficiency in the amount of oxygen that was able to make it to his tissues, an excess of CO2 in his tissues, and long-term effects in how his body is able to maintain and repair itself.
At the same time, the report indicated that Scott Kelly experienced no significant changes when it came to cognitive performance. The preliminary findings touched on this, indicating that Scott showed a slight decrease in speed and accuracy when undergoing cognitive performance testing compared to his brother. This decrease was more pronounced when he first landed, but was attributed to readjustment to Earth’s gravity.
Mathias Basner – a professor at the University of Pennsylvania, Philadelphia, who was in charge of conducting the tests – also found no real difference in cognition between 6 month and 12 month missions. This is especially important since typical stays aboard the ISS last six months, whereas long term missions to Mars would take 150-300 days – depending on the alignment of the planets and the speed of the spacecraft.
A two way trip to Mars, as well as the time spent in Mars lower-gravity environment (37.6 % that of Earth’s), could take multiple years. As such, the Twin Study was intrinsic to NASA’s efforts to prepare for its proposed “Journey to Mars“, which is expected to take place sometime in the 2030s. These and other studies being conducted aboard the ISS seek to determine what the long-term effects on astronaut health will be, and how they can be mitigated.
The NASA Twin Study was the result of a partnership between 10 individual investigations, 12 colleges and universities, NASA’s biomedical labs and the National Space Biomedical Research Institute Consortium.
Scott Kelly’s stay in space and the Twin Study will also be the subject of a PBS documentary titled “Beyond a Year in Space“. Be sure to check out the teaser trailer here:
Why do some astronauts come back from the International Space Station needing glasses? Eye problems are one of the largest problems that have cropped up in the last three to four years of space station science, affecting 20% of astronauts. And the astronaut office is taking this problem very seriously, pointed out Scott Smith, who leads the Nutritional Biochemistry Lab at the Johnson Space Center.
It’s one example of how extended stays in flight can alter your health. Despite NASA’s best efforts, bones and muscles weaken and months of rehabilitation are needed after astronauts spend a half-year on the space station. But in recent years, there have been strides in understanding what microgravity does to the human body — and how to fix it.
Take the vision problem, for example. Doctors believed that increased fluid shift in the head increases pressure on the optic nerve, a spot in the back of the eye that affects vision. There are a few things that could affect that:
Exercise. Astronauts are told to allot 2.5 hours for exercise on the International Space Station daily, which translates to about 1.5 hours of activity after setup and transitions are accounted for. Weight lifting compresses muscles and could force more blood into their heads. NASA installed an advanced Resistive Exercise Device on the space station that is more powerful than its predecessor, but perhaps this is also causing the vision problem, Smith said. “It’s ironic that the exercise device we’re excited about for working the muscles and bone, may hurt eyes.”
CO2 levels. This gas (which naturally occurs when humans exhale) is “relatively high” on the space station because it takes more power and more supplies to keep the atmosphere cleaner, Smith said. “Increased carbon dioxide exposure will increase blood flow to your head,” he said. If this is found to be the cause, he added, NASA is prepared to make changes to reduce CO2 levels on station.
Folate (Vitamin B) problems. Out of the reams of blood and urine data collected since before NASA started looking at this problem, they had been looking at a biochemical (nutrient) pathway in the body that moves carbon units from one compound to another. This is important for synthesizing DNA and making amino acids, and involves several vitamins and nutrients. After scientists started noticing changes in folate (a form of Vitamin B), they probed further and found an interesting thing regarding homocysteine, a type of amino acid at the heart of this one carbon pathway. It turns out those astronauts with vision issues after flight had higher (but not abnormal) levels of homocysteine in their blood before flight, as published here.
“It’s speculating, but we think that genetic differences in this pathway may somehow alter your response to things that affect blood flow into the head,” Smith said.
After finding these essentially “circumstantial” evidence of a genetic predisposition to vision issues, they proposed an experiment to look at genes associated with one carbon metabolism. “To give you an idea of the importance of this problem, we went to every crew member that’s flown to space station, or will fly to space station. We asked if they would give us a blood sample and look at their genes for one carbon meytabolism,” he said. “We approached 72 astronauts to do that, and 70 of them gave us blood, which is unheard of.”
While NASA tries to nail down what is going on with astronaut vision, the agency has made substantial progress in preserving bone density during flights — for the first time in 50 years of spaceflight, Smith added.
We mentioned the advanced Resistive Exercise Device, an orbital weight-lifting device which was installed and first used during Expedition 18 in 2008 and has been in use on the space station ever since. It’s a large improvement over the previous interim Resistive Exercise Device (iRED), which didn’t provide enough resistance, allowing some astronauts to “max out” on the device and could not further increase weightlifting loads after some weeks or months of use.
“We flew the iRED on station and the bone loss on station looked just like it did on Mir, that is, with no resistive exercise device available,” Smith said. But that changed drastically with ARED, which has twice as much loading capability. Crews ate better, maintained body weight and had better levels of Vitamin D compared to those that went before. Most strikingly, they maintained their bone density at preflight levels, as this paper shows.
While we think of bone as being cement-like and unchanging (at least until you break one!), it’s actually an organ that is always breaking down and reforming. When the breakdown accelerates, such as when you are not putting weight on it in orbit, you lose bone density and are at higher risk for fractures.
Why is unknown, except to say that the bone seems to rely on some sort of “signalling” that indicates loads or weights are being put on it. Conversely, if you are to put more weight on your bones — maybe carrying a backpack with weights on it — your skeleton would gradually get bigger to accommodate the extra weight.
While it’s exciting that the ARED is maintaining bone density, the question is whether the body can sustain two processes happening at a faster rate than before flight: the breakdown and buildup of bone. More study will be needed, Smith said, to pinpoint whether this affects the strength of the bone, which is ultimately more important than just mineral density. Nutrition and exercise may also be optimized, to further allow for better bone preservation.
That’s one of the things scientists are excited to study with the upcoming one-year mission to the International Space Station, when Scott Kelly (NASA) and Mikhail Kornienko (Roscosmos) will be one of a small number of people to do one consecutive calendar year in space. The bone “remodelling” doesn’t level off after six months, but perhaps it will closer to a year.
Smith pointed out the quality of health data has also improved since the long-duration Mir missions of the early to mid 1990s. Specific markers of bone breakdown and formation were just being discovered and implemented during that time, whereas today they’re commonly used in medicine. Between that, and the fact that NASA’s Mir data are from shorter-duration missions, Smith said he’s really looking forward to seeing what the year in space will tell scientists.
Small populations make it really hard to do scientific studies, because the sample size may not be representative of the population being studied. And that’s the challenge with spaceflight, right before you start: only so many people head up there and take part of your experiments. With less than 20 people heading to space per year these days, that’s a tiny population to do medical studies from.
“One of the advantages that terrestrial medicine has is a lot of people to study,” said Jean Sibonga, the bone lead of NASA’s human spaceflight program. “While we’re acquiring our data using the conventional clinical methods for testing bone health here on Earth, terrestrial medicine is running these same studies and getting the results sooner.”
But for a small group being studied, the science is highly professionalized. NASA’s scientists are part of many professional societies ranging from anesthesia to bone science to nutrition. They collaborate with people all over the world. And slowly, as the results come in, they say they are making progress in understanding how space deconditions our bodies and how to make them stronger again.
With bone — where for decades, physicians have tried to figure out which populations are most at risk for fractures — comes an example of another hurdle. The astronauts are young, usually 50 or below, making them statistically one of the least at risk for fractures until they expose themselves to microgravity. This means that comparing them to seniors is “clearly not an appropriate test for our population,” Sibonga said.
But for what it’s worth, NASA has adapted international clinical guidelines to identify astronauts who have optimal bone health, and to see if the “countermeasures” — weight-bearing exercises — are having any success. This also means looking at the astronaut’s entire picture of health, from family history to medication intake to hormone levels, to see if these variables have any sorts of effect. (More on the results of these tests tomorrow.)
The issue with astronauts, Sibonga said, is they go through very rapid bone losses — even faster than what postmenopausal women experience. Astronauts lose about 1% of their bone density on average per month from their hip and spine. In aging women, vertebrae are the most affected and they can find themselves with “compression fractures” where the vertebrae collapse and their backs are stooped over.
Astronauts may be at risk, but it’s hard with tests on the space station to see if this is happening real time. This work has to wait until they get back to Earth. Sibonga said NASA is trying to fix that. “We’re doing market surveys, and if we find a promising technology for inflight monitoring, we will work to develop and validate these tests in these astronauts.”
Sometimes that technology comes from other sectors. The idea of “loading” not only applies to human health, but also to engineering. So some of the same models could have relevancy between engineering and humans. One device NASA has been testing on the ground is a quantitative computed tomography (QCT), an imager that quantifies the amount of bone mass an astronaut has in true three dimensions. From these QCT data, engineers can develop models to estimate the mechanical loads that would cause a bone to fracture. But only a handful of people have applied this engineering model to biological systems, Sibonga said.
Naturally, NASA is also interested in how much bone mineral density (BMD) comes back after a mission. BMD tests are done every three years in astronauts from the time they are selected (bearing in mind the technology was not available until about the mid-1990s). Uniquely, NASA also invites its astronauts back after they leave or retire to continue the tests — a practice even the military branches in the United States don’t do. This allows the agency to do long-term population studies on its astronaut corps.
Sibonga added that NASA’s science is proceeding at an aggressive pace, given the small population and mission schedules, and cited a few examples of research papers on skeletal health and femoral strength as examples.