A study of 13 astronauts, each of whom spent about six months on the International Space Station, found that their hearts had adapted to weightlessness and then coped with a simulation of Martian gravity. Cardiologists at Northwestern Medicine led the work, which appeared in the journal Circulation.
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James Thomas, a professor of medicine in cardiology at Northwestern University Feinberg School of Medicine and the senior author, said the data give reason to think a crewed trip to Mars is feasible as far as the heart is concerned. The sample is small and the design is exploratory, so the finding is encouraging rather than conclusive.
Echocardiograms before, during and after six months in orbit
According to the ScienceDaily report of Oct. 21, which says the human heart “may be surprisingly well equipped for a journey to Mars,” the researchers collected echocardiograms, which are ultrasound scans of the heart, before, during and after each mission. In orbit, astronauts scanned one another every few weeks and sent the recordings to Earth, where Thomas coached them in real time. The paper, “Impact of Prolonged Spaceflight on Cardiac Structure and Function: An Exploratory Longitudinal Observational Study,” is registered under DOI 10.1161/CIRCULATIONAHA.125.078665.
The authors are Vinesh Appadurai, Kazuaki Negishi, Allen Borowski, Zoran Popovic, Neil Greenberg, David Martin, Michael Bungo, Benjamin Levine and Thomas, drawn from Northwestern Medicine, UT Southwestern Medical Center and McGovern Medical School at UTHealth Houston.
Early dip, then recovery toward pre-launch levels
In the first two weeks in space, the amount of blood filling the heart and the volume pumped with each beat both declined. Those changes did not persist. As missions continued, both measures gradually improved toward their pre-launch levels. That pattern fits what is known about the loss of gravity: fluid shifts upward in the body and the heart, working less than it does on the ground, loses some mass. Thomas has described the effect in terms of muscle, saying astronauts lose both muscle mass and cardiac mass because they do less work in a weightless environment, which is why exercise is central to the crew’s routine.
The exercise load was substantial. Under NASA’s Exercise Countermeasures program, astronauts trained for up to two hours a day, with 30 to 45 minutes of endurance work and 60 to 75 minutes of resistance work. NASA’s own explainers on cardiovascular health in microgravity and on its exercise requirements for crews describe why that training is built into every long stay on the station.
Tilted 22 degrees to mimic Mars at 38 percent of Earth gravity
The Mars test came after the astronauts returned. Each was tilted upward by 22 degrees from lying flat, a position that shifts blood toward the lower body in a way that approximates Martian gravity, which is about 38 percent of Earth’s. Their hearts performed under that simulated load as well as they had standing upright on Earth before launch. The authors say it is the first study to examine heart response to simulated Martian gravity after an extended stay in space. Astronauts also generally handled the blood pressure drop that can occur on standing after landing, which the report links to their training.
Thomas offered a measured reading of the results. In the report he said there is now reason to think a journey to Mars could be made, and he stressed that exercise in space is crucial to counter the loss of muscle and cardiac mass.
Limits of a simulation
The caveats are in the report itself. The sample of 13 is a small number, the design is observational and exploratory, and a tilt table on Earth is not Mars. A real trip would add months of transit in weightlessness before any time in partial gravity, plus radiation, bone and muscle loss, and the demands of landing and working on the surface. The study measured a specific set of heart functions during a station stay of about six months, which is shorter than a round trip to Mars would be. Because the astronauts were their own controls, scanned before launch, during the mission and after landing, the comparison is within individuals rather than against a separate group, a strength that does not offset the small size of the cohort or the lack of a comparison group that did not exercise.
The research agenda around those pressures is broad, and NASA has written about counteracting bone and muscle loss in microgravity as part of the same problem. Funding for the cardiac study came from the National Space Biomedical Research Institute, NASA, the IDP Foundation, Sandra Helton and the National Heart Foundation of Australia. The reassuring result is that the heart did not fail the test that was run; what remains is longer missions, more astronauts and conditions closer to the real thing. Any decision about crew selection, exercise hardware or mission length for Mars would need that further evidence, not this single study.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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