How does going into space impact the human body?
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5, 4, 3, 2, 1. Sending astronauts into space is a pretty amazing feat. Building the spacecraft, launching it through the Earth's atmosphere and coming up with all these ways to live in zero gravity. But it doesn't always go according to plan. In my family, we talk about these possibilities

We discussed all of this. We never said we were going to be gone for nine months, but it turned out that way. I wanted to hug my husband and hug my dogs. And I'll say that in that order. That was Butch Wilmore and Sunny Williams. They're two NASA astronauts who set off on an eight-day mission to space. But they ended up on the International Space Station for nine months after their space capsule suffered from technical problems. And that got me thinking about how the body reacts when it spends so long in outer space.

And does it ever fully recover? I'm Hannah Gelbart and this is What's in the World from the BBC World Service. Well someone who knows a lot about outer space is BBC science presenter Caroline Steele who joins me in the studio now. Hello. Hello. Thank you for having me on. Yeah, you're welcome. So first of all we're very rooted down to the ground here using gravity. That's one of the main differences between Earth and space.

How would it feel to be in outer space without gravity and what are some of the other differences? I think it would feel pretty weird. I've never done it myself, but I think it's a bit like scuba diving. If anyone's been scuba diving, you have no sort of pull in any direction and feel kind of weightless. A couple of other differences are here on Earth, we have a lovely atmosphere that gives us air to breathe. We can breathe quite easily.

Yeah. Yeah, which is good. And you don't have that in space. You need help to breathe. The atmosphere also keeps us at kind of a constant temperature. Whereas in space, if you're in direct sunlight, it can be like over 100 degrees Celsius. And if you're in the shade, it can get to colder than minus 100 degrees Celsius.

And also the Earth has a magnetic field, which we don't really notice, but it's protecting us from radiation from the sun and radiation from the rest of space. And when you're outside of the Earth's magnetic field, you don't have that extra protection. So, yeah, gravity, atmosphere and the magnetic field are probably the three main differences between Earth and space. I imagine that the longer you are in space, the more all of these factors that you've outlined would impact your body. How does it affect the body?

So one of the big ones is the lack of gravity basically means that your body isn't having to work as hard to sort of stay upright. Like our bodies work quite hard to keep us upright and not just sort of splatted down on the ground. So when you spend time in space, you lose bone density because your bones aren't working as hard to keep you upright. And you lose muscle mass because your muscles aren't working as hard to keep you upright. You can actually lose 20% of your muscle mass in just two weeks.

in space. So it has a huge impact on your body and the muscles that suffer the most are the ones kind of related to your posture. So the muscles in your neck and your back. This lack of gravity also affects the fluid in our body. So right now whilst we're sitting down, the sort of

blood in our bodies is also being drawn down to the ground by gravity and then our heart is working really hard to sort of keep it up and evenly distributed throughout our bodies. But when you go into space and there's no gravity, the fluid in your body sort of starts moving up and can pool in the head. So

Quite often, astronauts get a kind of puffy face within a few days of arriving in space because all the fluid is pooling in their head. What about their eyes? Don't the eyes have fluid too? Yeah, and it has a huge impact on astronauts' vision. So the extra fluid kind of presses on the eyeball. And 40% of astronauts have lasting eye damage from going to space. So not only is your vision affected up there, for a lot of people, it never goes back to normal again.

Another big impact is the radiation. So we've not got the Earth's magnetic field keeping you safe from radiation in space. So you're much more exposed to that. And that can lead to changes in your genes and it can lead to mutations which can eventually go on to cause cancer. So that's another big effect of being in space. How are these impacts measured?

So if you're on the International Space Station, you wear what's called a Geiger counter, but it's basically like a radiation counter around your neck. So you know exactly how much radiation you've been exposed to, which doesn't protect you from it. But it means that you kind of make decisions in the future based on how much radiation you've been exposed to. So if you happen to be in space when there was more radiation than normal, maybe you're not going to be allowed to go on another mission in a few years because you've already kind of met your quota.

Another big impact of going into space is a lot of people feel sick, kind of like travel sick. And that's because in our ears we have these sort of canals filled with fluid and the fluid moves around and it helps you be balanced. It sort of tells you about the position of your body. And when you go into space and there's no gravity, this fluid starts to move differently, which can make astronauts feel quite sort of motion sick.

And that's a problem because when you're in charge of a spacecraft, you need to be able to do your job. So NASA used to train its astronauts by spinning them in essentially sort of a spinny chair and then stopping the chair. And then the fluid in your ear is still spinning. But the information from your eyes says, hang on a second, we're still we're not moving.

And that sort of disagreement between what's going on in your ear and what your eyes are telling you makes you feel sick. And then they'd get astronauts to do all different kinds of complicated tasks to check that they can still function well while feeling dizzy and sick.

That sounds awful. Sounds pretty bad, yeah. And there was a study I read about with some Russian twins because apparently being in space can also make you age faster. Yeah, so it affects your genetics and that's one key way of looking at how we age. So there were the Russian twins. There's also NASA sent one twin into space in 2015, a guy called Scott Kelly. And he has a twin called Mark Kelly, who's also an astronaut, and he stayed on Earth. So Scott spent a year in the International Space Station whilst Mark...

Mark spent a year in the US and they collected bloods and feces and urine samples from the twins whilst they were in space or on Earth and sort of compared them when they got back. Because that's a difficult thing. It's kind of hard to study these imaginations.

because you don't know how someone would have been if they stayed on Earth and didn't go into space. And there were some pretty big differences between Scott and Mark. So when Scott got back, he was five centimetres taller. And that was basically because gravity wasn't pulling down on him and his spine stretched out. He had lost 7% of his body mass because of not using his muscles as much. Meanwhile, his twin had gained weight.

genes had changed and a lot of that went back to normal. 93% went back to normal after six months but it didn't all go back to normal. There were some lasting genetic changes to Scott which is quite interesting and his eyesight changed, the shape of his eyeball changed and he had sort of lasting vision changes. So there are really serious risks to going into space but these

these are risks that people like astronauts are willing to take. Yeah. How do they have to prepare apart from being spun around in chairs before their missions? So you ideally go into space in the best shape you've ever been in in your whole life. So they do loads of cardio training. They do loads of weightlifting. So the sort of...

bone density loss and the muscle mass loss doesn't matter as much. One really cool thing that they do is, so NASA has a giant swimming pool with a complete replica of the International Space Station submerged at the bottom of it. And in preparation for going to the International Space Station, astronauts put on these like weighted...

They look exactly like spacesuits, but they're designed to be worn underwater. And they have to go down into the International Space Station, experience weightlessness, and do all the different complicated tasks that they have to do that are incredibly important. They also do a lot of quadrupedal

core work because when you've not got the kind of stability of gravity holding you down and you're sort of twisting and moving in space your core becomes really important so they essentially go into space super fit with really strong cores and kind of experience of being in the international space station because they've been in a replica in a weightless environment so ideally nothing really takes you massively by surprise.

And when you're out in space, you've got to do a lot of exercise too. So I'm going to play you a clip now of Peggy Whitson, who is an astronaut who holds the world record for the woman who has spent most time in space, not in one go. She spent 675 days there.

Here she is. So in order to counteract some of these negative effects, in particular the bone loss, we have what's called a resistive exercise device. You know, normally on the earth, they would recommend that you lift weights. And of course, there's no weight in zero gravity. So you have to work against your resistance. And of course, when you know if you're losing bone mass that

1% per month, you're very motivated to do the exercise. So it's about 45 minutes to an hour every day of resistive exercise.

So as well as doing resistive weight training, astronauts on the International Space Station also run on a treadmill, which is kind of hard to imagine because there's no gravity. So how can you run? But I've watched videos of it and they're sort of like strapped down into this treadmill and running. And ideally, they're doing two hours of exercise every day to avoid this muscle loss and this bone density loss.

What else do organisations like NASA do to keep astronauts safe, especially from the risks, the radiation that we've talked about? So on the International Space Station and other spacecraft, they're sort of shielding from radiation. So I think the International Space Station basically has a layer of aluminium that reflects away some of the radiation. And areas where astronauts spend more time, like in the sleeping quarters, there's more shielding.

Plus, if they're leaving the spacecraft and going out on a mission, maybe fixing something on the outside or one day walking on the surface of the moon or walking on the surface of Mars, you watch the sun, which is one of the main sources of radiation, and see what's going on and only leave the spacecraft there.

at times when the sun is less active, so you're less exposed to radiation. But yeah, it is kind of an unavoidable fact of going into space. You can't get rid of the radiation risk completely. You can just try and minimise it as much as possible. And of course, also not allowing astronauts to spend years and years in space because the longer you're there, the higher your risk. And there's protective clothing too, right? Space suits? Exactly, yeah. They have sort of shielding layers in there to protect you from radiation, give you oxygen to breathe when there's no atmosphere, make sure you're sort of...

to stable pressure and things like that. And there's something quite interesting that

that happens on the International Space Station to avoid eye damage. Do you know how I said that sort of your fluid can pool in your head, gives you a puffy face, damages your eyes? There are these kind of like vacuum trousers that people can wear that sort of suck the fluid back down your body like gravity would on Earth and stop it from pooling in your head. So people spend a period of time wearing these vacuum trousers to try and reduce the eye damage. So there are sort of clever solutions like that. And there's also, you know, a lot of science going into this, a lot of things...

Things like Scott and Mark Kelly, where you're trying to study people to find out exactly what happens in a sort of more controlled, shorter environment, like on the International Space Station. Because when we go to Mars, you know, people are going to have to spend years in space. We really need to know exactly what the risks are so people know what they're signing up for. And so we can protect people as well as possible.

So, Caroline, what is the recovery like when astronauts come back to Earth? How long do they take to recover? You've mentioned some things that they might never fully recover from. So it sort of varies from person to person how long it takes you to get back to normal. And some people never get completely back to normal. So, for example, with astronauts,

eyesight, some people's eyesight changes for the rest of their lives and that never goes back to normal. But astronauts work with sort of a dedicated team when they land back on Earth who work with them to get them back in the best shape possible to get over this muscle loss and this bone density loss. And the radiation and potential genetic changes, there's nothing you can really do to sort of undo those changes. But astronauts are sometimes monitored to see what the differences are and how long they last. Amen.

I imagine when there are more tourist missions being sent out, more tourists going out on spacecraft, that there are going to be some pretty long forms that we have to sign. Yes, I can't imagine the waiver you have to sign to go into space, even for 10 minutes. I imagine it's really long, yeah. Caroline, thank you so much. Thank you. Thank you.

And thank you for joining us. And if you want to hear more from Caroline, she's a regular on the podcast. She has been right here in the studio with me chatting about the Northern Lights, what causes them, how to get the best pictures of them and space junk. Why is it such a problem and how do we get rid of it? You can find those episodes wherever you get your BBC podcasts. I'm Hannah Gelbart. This is What's In The World from the BBC World Service. And we'll be back with another episode soon. See you then.