What Happens to Humans if They Live in Space Too Long?


Answer by Robert Frost, engineer/instructor at NASA

We don’t know the answer to that. But every crew that resides on the International Space Station provides us information that we use to adjust our protocols and that extends that period of time.

The longest contiguous amount of time a human has spent in space is 437 days. That was done by Valeri Polyakov, almost twenty years ago. That was his second flight. His first was 240 days long.


Sergei Krikalev, over six flights, has spent 803 days in space.

Space is a harsh environment for humans. We didn’t evolve to live there. Systems throughout our body have evolved to function under the stresses of gravity.

Our muscles are constantly working against gravity, on Earth, and those muscles have less work to do in space, and so they atrophy. That includes the heart, which shrinks a little, the neck muscles that hold up our heads, and our calves.

Since our bones are not experiencing the loads they experience on the ground, they feel no need to maintain themselves. Bone tissue is absorbed and not rebuilt. This absorbed bone can cause kidney stones. The places where the bone has weakened can easily fracture.

Here’s a graphic that shows the rate of bone loss for various parts of the body.

There is evidence that extended periods in space can result in dysregulation of the immune system. While there isn’t too much risk of exposure to pathogens, a compromised immune system can result in autoimmune responses and hypersensitivity.

Aside from the deleterious affects of microgravity, a potentially larger threat is radiation. We take for granted how much our planet protects us from radiation.

Out in space, astronauts are exposed to —> Read More