Health in orbit

How does space travel affect the human body?

August 29, 2022

NASA is preparing for lift-off with its next generation megarocket, with ambitions of putting the first humans on Mars. The most powerful rocket ever built is undergoing a rigorous stress test before it’s deemed safe to carry astronauts. But how will astronauts fare in space, further away than they have ever been before? Cardiologist and space exploration enthusiast Professor Jason Kovacic explains what you need to know about NASA's first moon mission since Apollo, and the impacts on heart health in outer space.

How did you start researching this area?

I have always been fascinated with astronomy and space exploration, and also have a deep interest in the effects of exercise and sports on the heart. In many ways space travel is basically the opposite of exercise training – it involves living and working in an environment with zero or minimal gravity, which places far less physiological demand on our heart and muscles. Indeed, some of the earliest data on what might happen when we spend prolonged periods in space came from the 'Dallas Bed Rest Studies' conducted in the late 1960’s – where subjects were prohibited from exercising and were placed on bed rest for 21 days. Similar to space travel, this 21 day period of bed rest led to reductions in heart performance in the range of 20-30%. So, the impacts of space travel on heart health is something I am very much interested in.

How does space travel affect the human body?

Firstly, lack of gravity causes a whole lot of problems with muscle wasting, and that's including the heart muscle and muscles of our arms, legs and trunk. As we've seen when astronauts go up to the International Space Station for up to almost a year at a time, many are actually unable to initially stand up and walk when they return to Earth because their muscles are so deconditioned. That can create profound problems, and if people are going to Mars, they may be gone for years at a time. We've never had people in space for that long. So the lack of gravity and the effects on muscle and muscle wasting will be really important.

Zero gravity also leads to changes in the blood, including shrinking of the blood volume and potential changes in blood flow. In addition, there was a recent blood clot found on an astronaut from the International Space Station, that has led to follow-up studies where abnormal flow characteristics in microgravity conditions were found in certain veins in the neck. It appears that the lack of gravity leads to some slower flow of blood through certain parts of the body which could be a setup for a blood clot.

Other major issues for deep space travel will include a change in the inflammatory profile and our immune systems.

What other environmental factors in space will impact the human body?

Exposure to radiation is a factor in orbit, there are a number of radiation sources in space and some of these are able to penetrate through the side of spacecraft and spacesuits. Long-term exposure to radiation may be a critical problem in terms of causing changes to our DNA and setting up for DNA mutations that may cause cancer. All of this remains theoretical, but is certainly of major concern to scientists working to make things safe for future long-term humans in space.

It's interesting to note that on Earth, we're largely shielded from different forms of radiation and ‘cosmic rays’ due to the magnetic field and atmosphere around the Earth. But Mars and the moon don't have a magnetic field or significant atmosphere like the Earth does. So astronauts on Mars and the moon will be exposed to far higher doses of radiation and cosmic rays than we get exposed to here on Earth.

Yet another important issue to plan for will be mental health and isolation. If there's a medical emergency, for example someone has something simple like appendicitis, how are they going to manage that up on Mars or the moon? If people have these kind of problems up on Mars and the moon, they'll be largely on their own. Because of their there will be some need to train people to manage basic medical emergencies independently.

Specifically, how does space travel impact the heart?

The key issue related to the heart will be deconditioning and weakness of the heart muscle. The medical word for this is ‘atrophy’, which means a weakening of the heart muscle and less heart strength. That's largely because the heart will not have to pump against gravity. Normally when we are standing, the heart has to be able to overcome gravity and generate the pressure to get blood up to our head and to help return blood from our feet up to our chest. In space there's zero gravity, and there is also there is far less gravity on the moon or Mars than on Earth. Deconditioning and changes of the heart muscle over months and years may also lead to problems with the heart’s rhythm – although we don’t know much about this yet. All of this may lead to real challenges with bringing these people back home to Earth. People that have been in the International Space Station for up to a year in zero gravity are initially unable to walk, but they are able to be reacclimatised to the Earth. But if someone's been in a low or zero gravity environment for several years, which will be the case when people go to Mars, whether or how they'll be able to be rehabilitated back to Earth remains to be seen.

To summarise, there is a lot to be considered about the heart and spending long periods in space – heart deconditioning and weaking, changes in blood flow and blood clotting, exposure to radiation, rhythm problems, and other factors.

How could mental health be affected on a mission to Mars?

Apart from the heart and blood vessels, another major issue will be mental health. Long term astronauts will need to endure prolonged solitude and isolation. Sure there'll be teams of several people going into space each time, but they'll be needing to manage conflict resolution, medical emergencies, and to operate under severe and extreme environments for years at a time without physical backup. This is going to be a really challenging mental exercise. Humans have just not been through that for an extended period of time. Scientists have been looking at what happens when you send people to Antarctica or the South Pole as they spend months at a time in isolation down there. But still they're on the same planet, and they can be rescued in warmer months when the weather allows. On Mars, there will be no ability to rescue travellers.