Staying in space represents the fulfillment of humanity's age-old dream, but it also brings immense challenges for the human body. In the microgravity environment, far from the familiar conditions on Earth, our bodies begin to behave in completely different ways. Bones lose density, muscle mass decreases, the heart and blood vessels undergo unexpected adaptations, and even the immune system changes. These transformations are not just a scientific curiosity; they directly affect the health and success of astronauts' missions, especially during long-term stays at locations like the International Space Station (ISS). However, it is precisely the study of these negative effects that opens the door to revolutionary medical insights with the potential to improve healthcare for all of us on Earth.

Space as a unique medical laboratory

The research of the European Space Agency (ESA) is not limited to ensuring the safety of astronauts. Studying the effects of spaceflight on the human body offers a unique insight into medical conditions that affect millions of people on our planet. Problems like osteoporosis, muscle atrophy, and cardiovascular diseases develop over years on Earth, while in space, similar processes occur much more rapidly. This turns the space environment into a kind of medical laboratory where scientists can study disease mechanisms and test new therapies in a relatively short time. The knowledge gained in orbit has the direct potential to benefit everyone, from the elderly population facing the consequences of aging to patients recovering from serious injuries or long-term illnesses.

A key role in these efforts is played by ESA's SciSpacE program, which brings together scientists from all over Europe to investigate how space stressors – weightlessness, isolation, and cosmic radiation – affect human physiology. Investigations are conducted on two fronts: directly on the International Space Station, but also on Earth through so-called analogue studies. The most famous among these are the long-term bedrest studies, during which volunteers spend weeks, and even months, lying with their heads tilted downwards to simulate the conditions of microgravity as closely as possible, especially the redistribution of body fluids and the lack of load on the skeleton and muscles.

In focus: the bone and heart health of astronauts

As part of the Ignis mission on the International Space Station, a series of key European experiments were conducted that focused on fundamental areas of human health, primarily bone health, cardiovascular function, and muscle performance. Two systems are particularly sensitive to the lack of gravity: the skeletal and the cardiovascular systems.

One of the most pronounced consequences of staying in space is the loss of bone mass. Without the constant load provided by the force of gravity on Earth, bones lose calcium and become more fragile at a rate that is incomparably faster than that in older people with osteoporosis. A study called Bone Health is investigating in detail whether astronauts experience a specific type of bone weakening after short-duration missions, a phenomenon known as Post Re-Entry Bone Loss (PREBL). By collecting bone density scans, blood samples, and activity data, researchers hope to better understand how the skeleton recovers after returning to Earth and what mechanisms underlie this process.

In parallel, the Bone on ISS experiment deals with long-term changes in the bone structure of astronauts who have flown multiple times. Using sophisticated molecular markers, scientists are tracking how bones remodel in space. The ultimate goal of this project is to develop a "digital twin of bone" – a virtual model that can predict with high precision how an individual astronaut's skeletal system will react to space conditions. Such a tool would allow for the creation of personalized countermeasures and exercise plans, thereby minimizing the risk of fractures and long-term damage.

ESA is also intensively researching the effects of spaceflight on the heart through the Cardio Deconditioning study. In microgravity, the heart does not have to work as hard to pump blood through the body, which can lead to its shrinkage and loss of capacity over time. Scientists use advanced imaging techniques, such as magnetic resonance imaging and ultrasound, and compare data from space missions with those from terrestrial bedrest studies to understand how staying in space and exposure to radiation affect cardiovascular health. These findings not only help protect astronauts but also provide valuable information for treating heart disease on Earth.

Fighting muscle atrophy: Innovative solutions from orbit

Along with bones, muscles are among the first to be affected in a weightless state. Without the need to counteract gravity with every movement, muscle fibers quickly begin to deteriorate, leading to a significant loss of mass and strength. To counter this challenge, ESA is testing an innovative technique known as neuromuscular electrical stimulation (NMES). This method applies mild, controlled electrical impulses to the leg muscles, stimulating their contraction without the conscious effort of the astronaut. The goal is to maintain strength, endurance, and muscle mass during long-duration flights, thereby reducing the time needed for rehabilitation upon return.

The experiment called Muscle Stimulation, in which astronauts like Matthias Maurer also participated, includes a comprehensive package of assessments, from magnetic resonance imaging (MRI) and microcirculation analysis to blood sampling, to accurately evaluate the effectiveness of NMES in space. Polish astronaut Sławosz Uznański also conducted a series of experiments related to human physiology during his stay in the Columbus module. The potential of NMES technology is also huge on Earth – it could help patients with limited mobility, people recovering from surgery or injuries, as well as the elderly population in the fight against sarcopenia, or the loss of muscle mass associated with aging.

From space to Earth: Concrete benefits for global health

All of this research, from bones and muscles to the heart and cells, is part of a broader goal: to make human space exploration safer and more sustainable for future generations who will travel to the Moon, Mars, and beyond. However, they also reflect the immense value of space science for humanity. By observing the human body in the extreme environment of space, ESA is discovering new knowledge that directly contributes to improving healthcare on Earth. The work being done on the International Space Station is pushing the boundaries of science. It not only prepares us for life beyond our planet – it helps us live healthier lives right here at home.

Source: European Space Agency