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Spending time in space and having an unrivalled view of planet Earth is an experience many of us dream of, but the human body evolved to function in the gravity of Earth. So fully recovering from spending time in the weightlessness of space can take years.

“It’s a fact that space is by far the most extreme environment that humans have ever encountered and we’ve just not evolved to handle the extreme conditions,” Professor Damian Bailey, who studies human physiology, says. To begin with, the heart and blood vessels have an easier time as they no longer have to pump blood against gravity — and they start to weaken. And the bones become weaker and more brittle. There should be a balance between the cells breaking down old bone and those making new, but that balance is disrupted without the feedback and resistance of working against gravity. “Every month, about 1% of bones and muscles are going to wither away — it’s accelerated ageing,” Professor Bailey says.

Microgravity also distorts the vestibular system, which is how you balance and sense which way is up. In space, there is no up, down or sideways. It can be disorientating when you go up — and again when you return to Earth.