A Canadian astronaut explains the toll space travel takes on the human body

Imagine someone were to offer you a job.

It'll be incredibly interesting — full of adventure and excitement and intellectual stimulation. But it does have a few drawbacks, having mostly to do with the working conditions.

The environment you'll be working in comes with risks. To start with, it will age you faster. Your bones and muscles will atrophy. You're going to have issues with balance and disorientation. You may develop skin conditions. Your circulatory system will suffer. So, maybe, will your digestion and immune system. Beyond that, your risk of cancer will be increased, and there's a fairly significant chance of catastrophic – like deadly – workplace injury. The hours are long, the food will be terrible, you'll be separated from friends and family.

Those are the working conditions of astronauts — particularly those experiencing extended time in space, like those on the International Space Station, or those who might, some day, be aboard long duration missions to the moon or Mars. 

Canadian astronaut and physician Dave Williams, with co-author Elizabeth Howell, explore what we've learned about what space travel does to the human body in their new book: Why am I taller? What Happens to an Astronaut's Body in Space.

Here's Bob McDonald's conversation with Dr. Williams about the book.

This conversation has been edited for length and clarity

So how much taller did you get in space?

About an inch and three-quarters. In the absence of gravity, our spine, normally it's curved on Earth, but it straightens out when we're in space. And also our spine is made-up of different bones called vertebrae. And the space between those bones is where we have our discs. And that disk space gets greater in space. 

Well, if your spine is being stretched longer, doesn't that also stretch the spinal cord? 

Out of that you can get back pain. It turns out some astronauts will report more back pain in space than they have on the ground because of course the spinal cord sits inside those bony vertebrae. And if they're stretching out, won't that stretch the cord? And the answer is yes. So we've had astronauts experience tingling in the front part of their thigh relative to the stretching of their spinal cord that takes place in space. 

We talked about getting taller. Another one is the puffy face and bird legs. Tell me about that.

About 70% of the human body is water. When you go to space, in the absence of gravity all that fluid in your body shifts up to your chest and your face. So your face gets really puffy and your legs get really thin. Hence the phrase puffy face bird leg syndrome. In fact, I think I lost probably about two or three centimetres in the circumference of my thighs and my calf when I was in space. Just with that volume shift, it was really quite dramatic. 

What does that shift in fluid do to the circulatory system in the body?

The shift of fluids to the head may be related to some of those eye changes that we're seeing in space. It turns out that when you're in space, some people report they become quite myopic. It's difficult to read and this is called 'space flight adaptation, neurological syndrome.' We think it's fundamentally related to the fluid shifts causing thickening of the nerve layer in the back of the eye and then of course that changing how we perceive the images that we're looking at in space

We're beginning to understand more of this phenomenon and which of them are related to microgravity and then which of them may be problems if we go back to the moon or onto Mars.

You write that everything from bones to muscle to skin in the body literally breaks down in zero-G [gravity]. What's going on there?

There's a whole host of changes that take place and fundamentally they're all centred around the absence of gravity. Humans have evolved and grown on a gravitational environment on our planet. And in the future, when we go farther in the solar system we're going to be living in a partial gravitational world. 

But when we go from one place to another in microgravity, that lack of gravitational stimulus causes our bones to lose density, causes our muscles to become a little bit weaker. In fact, many of the research studies we do on Earth are done in bed rest studies and you can imagine when you're in bed for six months and you stand up the first time, your balance is going to be a little bit abnormal, your regulation of blood pressure, you're going to feel a little bit lightheaded standing up quickly and your muscles will be weak and your bone density decreases. So we have to understand all these phenomena to be able to travel farther into space. 

You also talk in the book about sophisticated exercise equipment on the space station to try to counteract those negative effects.

The exercise is absolutely critical and not surprisingly, this is a message that resonates with all of us, particularly as we get older on Earth. So to maintain our bone density as we age on Earth, we should be exercising. But in space we have to have exercise equipment to condition our heart and lungs — so aerobic exercise equipment like a cycle ergometer or a treadmill. And then we also have to have resistive exercise equipment, the equivalent of weightlifting on Earth to maintain bone density. And I can honestly tell you without a lie, I have cycled all the way around the world in 90 minutes.

Over the last few years, we've all learned the value of a healthy immune system. How is it affected in space?

We're studying that, looking at the microbiome of humans in space, their own microbiome and how their microbiome affects the International Space Station and what bacteria are growing on racks and things like that. But those immune changes are thought to be multifactorial. 

In other words, there's many reasons why we're getting them, one of which is simply the stress of being in space and the sleep shifting that's taking place and working in that unique environment. 

The immune system will get weaker. And interestingly, as a physician in space, I ended up treating my colleagues. And in fact both missions, it was for an infection. And what I was surprised about is the relative resistance to the antibiotics that I was using compared to treating the same medical condition on Earth. 

Tell me about what it feels like when you come back and experience gravity again

Well, balance — that is definitely a challenge. If you watch astronauts when we come back from long duration missions, you'll notice we have a bunch of assistants to help us simply stand up and be able to move around without falling over. The good news is that they recover very quickly once you start walking around on Earth.  

But there are also things that are called zero-G flashbacks and I remember flying a T-38 airplane probably about 3-4 weeks after my first space flight and I was banking the airplane and that actually took me back to microgravity. I felt like I was tumbling sideways, which isn't a good thing to feel when you're flying an airplane. But as an instrument pilot, you look at the instruments and that suppresses these other feelings that you're getting in your body. So everything worked out fine, but I thought it was an interesting phenomenon.

You're a physician. Given these health challenges associated with space travel, would you be ethically able to recommend space travel to a patient? 

Of course! I think part of that might be the informed consent process. You know, you list all the challenges and then say do you want to go? And I think everybody that I know would say yes.

Produced by Jim Lebans