Looking to future missions, Aggie researchers study bone loss in astronauts

NASA commercial crew astronaut Mike Hopkins performs physical training on the Advanced Resistive Exercise Device (ARED) at the agency’s Johnson Space Center in Houston. The device is used to simulate weight training while in zero-gravity environments.

When most people think about the equipment needed for a successful space mission, the human skeleton is probably not the first thing that comes to mind. But for two Texas A&M professors, bones have been the focus of more than 25 years of collaborative research supporting exploration beyond Earth.

Susan Bloomfield — professor and associate dean for research in the College of Education and Human Development — directs A&M’s Bone Biology Laboratory and works closely with Harry Hogan, a professor of mechanical engineering, associate dean for graduate programs in the College of Engineering and director of the Bone Mechanics Laboratory. Together with their students and staff, they have conducted extensive research into the bone loss astronauts experience during their time in space.

Fifty years after humans first walked on the moon, NASA has its sights set on Mars. And according to Bloomfield and Hogan, the phenomenon of bone loss will be an important factor to consider for future crewed missions.

Bloomfield said it’s important to understand that the changes observed in astronauts’ bones are a perfectly natural response to a weightless environment.

“Bone is a very smart tissue,” Bloomfield said. “It remodels and reshapes itself according to the demands put on it. So if my femur is now in space and I’m floating around using my arms more than my legs to navigate, that femur is not getting the normal bending stresses that it experiences, and it will say ‘well, we don’t need this much bone.’ ”

But while astronauts’ bone loss is due to normal human processes, Bloomfield said it took some time for scientists to detect and understand the extent of these changes. She said some of the early clues came during the 1970s from the astronauts manning NASA’s first space station, SkyLab. Though modern bone-imaging technology was not yet available, scientists did record high levels of calcium in the crew members’ urine.

“It rose within seven days of reaching space and stayed high for that period of time,” Bloomfield said. “So the body was losing calcium. … And the most obvious place [it was coming from] was bone because 98 percent of all calcium in the body is located in bone.”

As the space shuttle program began in the 1980s and more advanced X-ray technology arrived, astronauts’ bones could be examined before and after spaceflights, with bone density measurements being recorded for further study. Bloomfield said that as the data began to pile up, scientists arrived at a striking conclusion.

“One of our colleagues, a fellow named Adrian LeBlanc, published data from these [Dual Energy X-ray Absorptiometry] scans documenting that astronauts lose bone over their time in space at a rate 10-fold faster than your average post-menopausal woman here on Earth.”

The fact that physically fit, early-middle-aged crew members would lose bone so much faster than the group most prone to osteoporosis was certainly significant, Bloomfield said. But as Hogan says, it doesn’t become a major issue until stronger gravity reenters the equation.

“While they’re out there in space flying, the loads are low and the bones’ strength is low, so things are pretty well matched up,” Hogan said. “But then the danger is when you come back to Earth or if you’re going to Mars and you start loading the skeleton again.”

This increases the risk of fractures, Bloomfield said, which introduces a host of issues. For one, she said it remains unclear whether fractures heal normally in space. Also, an injured crew member would have a much harder time keeping up with the day-to-day tasks a mission may require.

“Even on a lunar base — that’s our next goal is going back to the moon — you can’t just zip back to the ER if you have a fracture,” Bloomfield said. “They’re going to have to treat medical issues on-site.”

For current missions on the International Space Station, Hogan said many see this problem as solved, thanks in large part to consistent exercise. Since traditional weights are out of the question in microgravity, ISS astronauts work out their muscles and bones with the Advanced Resistive Exercise Device (ARED), which uses resistance provided by vacuum cylinders to mimic the feeling of normal weightlifting.

“Given recent years and the higher quality exercise equipment that they have on the station now, they have found that if the astronauts follow the exercise prescriptions, then they can return to Earth with bone density levels that are quite similar to what they left with,” Hogan said.

However, Hogan said there are still many questions to be answered, and when it comes to overall bone strength, density isn’t everything. That’s where the work of people like him and Bloomfield continues. Like many others involved in this type of research, Bloomfield said they use lab rats to conduct more detailed experiments than those that would be feasible with humans.

To simulate the effects of microgravity, Bloomfield and Hogan's labs use a technique called “hindlimb unloading,” which Bloomfield said has been used for around 30 years by thousands of researchers. It involves putting the animals in harnesses that raise their back legs off the ground while still allowing them to move freely with their front legs. Researchers are then able to study the effects of this reduced weightbearing and the use of different treatments to maintain or recover bone.

Beyond exercise, other factors at play include nutrition and the use of osteoporosis drugs. Hogan said finding the optimal combination of drugs and exercise could prove useful for future space missions, potentially allowing crew members to reduce the hours they spend working out.

As humans look further beyond Earth, a whole new set of challenges comes into play, Bloomfield said. Sending people to Mars will mean more time in space, higher levels of radiation exposure and, for now, much less living space than what the ISS offers.

“Now we’re talking, say, a mission for Mars, which is two and a half to three and a half years, and the transit capsule that they’re planning on using now is quite small,” Bloomfield said. “There’s not going to be room for the exercise equipment that they have on ISS.”

Bloomfield said one thing many of these challenges have in common is that they necessitate an interdisciplinary approach — which also provides an excellent learning environment for students. Yasaman Shirazi-Fard, who holds a Ph.D. in biomedical engineering from A&M and worked with Hogan and Bloomfield during her time there, is continuing her work as an ISS mission scientist for NASA.

Hogan — who grew up fascinated by the space program and is now thrilled to be supporting it — said he loves seeing where their students end up.

“We’re really proud of our graduate students who are going on to bigger and better things and contributing in very important ways to human space exploration,” Hogan said.

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