Why microgravity could halt human exploration of Mars

25 January 2017

Interview with

Mark Wilson, Imperial College London

Microgravity has serious impacts on the body, including loss of bone, muscle and vision. Mark Wilson and Graihagh Jackson discuss why this is such a problem when journeying to Mars...

Mark - Well, there's different studies, but on average, the studies seem to show that people lose between one per cent and five per cent of their bone mineral density, per month that is, during microgravity. That's quite a lot if you're going to be spending nine months travelling somewhere. We don't know whether it plateaus off and some of the evidence from the International Space Station suggests that it does. But if it's not going to plateau off, then you're obviously going to have quite a lot of loss before you arrive.

Graihagh - The problem is that Mars does have gravity - not as much as Earth - but enough and that means you can’t lose too much otherwise you won’t be able to walk around on the surface. There’s a horrible phrase I’ve heard used to describe the problems of microgravity: you won’t trip and break a bone; you’ll break a bone and trip.

I.e. your bones are so thin and weak, gravity can snap them.

Mark - Well, because they aren't exercising in a normal way, and by that, I mean, when you normally exercise, you're walking or you're running, you have constant impact exercise, that's what helps bone turnover effectively. Because they haven't got that they lose bone mineral density and the other thing they haven't got is gravity pulling blood into the tissues. So even when people have exercised in space, for example, just running on a treadmill with braces to hold them on it, they still lose bone mineral density and muscle mass because although they've got impact exercise, they haven't got the gravitational force pulling blood into their legs. So, those are the two things; it's blood flow and impact exercise that are required to maintain bone mineral density and muscle mass.

We don't really know enough at the moment in terms of whether we can optimise things with hormonal treatments or with additional calcium and vitamin D and things like that. It does seem to be that really, to maintain bone mineral density and muscle mass, you have to be using them. And so, as drugs might offer a small benefit, it is unlikely to be the sole solution.

Graihagh - But bone density it’s Mark’s main concern...

Mark - My area of research is what happens to the brain in microgravity and hypoxia. What happens is is that because you haven't got gravity pulling blood into your legs, you get this fluid shift and we think that the intracranial pressure rises. What's happening is that you've got this reduced ability to drain venous blood. If you're sitting here now, you're putting about a litre of blood into your head every minute and that litre of blood has to get to get out every minute as well. When you have not got gravity helping that you can't drain blood quick enough.

What's happening, we're finding in longer space missions now, the chronic changes that are occurring are actually causing another phenomenon which is known as VIIP or Visual Impairment and Intracranial Pressure in space where the astronauts are losing peripheral vision and this is also a long-term problem that could be an issue in a mission such as one to Mars.


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