The health price of space travel is high, a study shows: stays in weightlessness can lead to irreparable bone damage and premature aging of some parts of the skeleton by up to ten years. The results underscore the importance of using special training programs in combination with medication to better protect astronauts from bone loss on future missions. The scientists say that the developments could also benefit the treatment of diseases of the skeletal system in general.
Everything floats – the release from the effects of gravity is fascinating, but it has long been known that being in weightlessness is not good for astronauts: the unnatural state disrupts human physiology and can cause various health problems. The loss of bone substance is particularly evident. “This already applies to today’s flights, during which astronauts are usually not exposed to weightlessness for more than six months,” says Anna-Maria Liphardt from the Friedrich-Alexander University of Erlangen-Nuremberg. Above all, this effect could reach a problematic level with the planned trips to Mars. “If people travel uninterruptedly in space for three years, we have to pay particular attention to the health risks,” says Liphardt.
Aged like after ten years
Together with other colleagues from Germany, Canada and the USA, the sports scientist has again investigated how the bone structure changes as a result of space travel and to what extent it recovers on earth. As part of a long-term study, the researchers examined 17 astronauts who spent months in weightlessness on the International Space Station ISS. Before their launch into space and six and twelve months after their return, the bone condition of the subjects was checked intensively. The scientists recorded the bone density and the strength of the tibia and the radius in the forearm. In addition, the condition of the internal microstructures of bone trabeculae (trabeculae) was examined, which play an important role in stability. The extent of bone turnover in the subjects was also measured using biomarkers in blood and urine.
As the researchers report, the critical consequences of weightlessness became apparent in their study results: nine out of 17 astronauts had not fully recovered twelve months after their stay in space and showed bone strength and mineral density reduced by up to two percent. That may not seem like much, but it isn’t, emphasizes Liphardt: “This corresponds to age-related bone loss of at least a decade. The consequence is that those affected have to reckon with the onset of osteoporosis and susceptibility to fractures much earlier,” explains the researcher. According to the scientists, it is particularly worrying that, in contrast to aging on Earth, it is less the bone shell that is affected in the astronauts, but rather the inner bone structure: some of the test persons already had irreparable damage to the rod-shaped trabeculae, the test results show.
Better countermeasures required
The importance of the length of stay once again became clear: “We were able to show that the longer the astronauts have been in space, the more difficult it is to regenerate,” says Liphardt. It was also shown that those astronauts were particularly affected by regeneration problems, in which a comparatively high bone turnover was determined before space travel. “Bone turnover means that cells are broken down and regenerated,” explains Liphardt. “People with higher levels of physical activity have higher bone turnover — the difficulty is maintaining that activity during the space mission.”
There are already various opportunities for physical activity on the ISS – from treadmills to bicycle ergometers to strength exercises. According to the study results, however, there is probably more demand and it is obviously important to adapt the training program better to the individual needs of the astronauts. “It is a special challenge to develop new devices that work in zero gravity and take up little space,” says Liphardt. Drugs are also already being used to counteract bone loss, which are also used in the treatment and prevention of osteoporosis. “Bisphosphonates are already being used by NASA, but we still don’t know enough about exactly how they work in microgravity,” explains Liphardt. Against the background of their results, the scientists now recommend examining the combination effects of drug therapy and physical training even more closely.
As they conclude, such research can not only benefit the health of astronauts. Because muscle and bone atrophy as a result of lack of exercise are also a central problem in chronic diseases on earth. “Our study could lay the foundation for new or adapted therapies,” Liphardt. Specifically, the researchers emphasize the use of a state-of-the-art computer tomograph as part of their astronaut study, with which they were able to directly image the inner bone structure in high resolution. Patients with diseases of the muscular and skeletal system at the University Hospital Erlangen can now benefit from this so-called HR-pQCT device.
Source: Friedrich-Alexander University of Erlangen-Nuremberg, specialist article: Nature Scientific Reports, doi: 10.1038/s41598-022-13461-1