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What Happens to the Human Body in Space?

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How can you stay healthy while experiencing the dream of living in space?

Have you ever dreamed of going to space? Space is a very severe environment. When we go to space, what sort of effects do our bodies experience?

©JAXA/NASA
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What sort of changes occur when you go to space?

Astronaut KANAI Norishige sitting in a rotating chair

Many people experience "space sickness"

On the ISS, or spacecraft that have flown into space, the force of gravity is much weaker than on the earth. As a result, many people show symptoms of "space sickness," such as headaches, nausea, and vomiting. When we are on the earth, we are strongly affected by the force of gravity. We have a small organ called the vestibular organ deep inside our ears (in the inner ear) that plays a key role in keeping our bodies balanced.
This organ converts information on gravity and acceleration experienced by the body into electrical signals and sends them to the brain. While on the earth, the brain always receives gravity information from the vestibular organs, and uses it to keep the body balanced.
In the low gravity of space, the information received from the vestibular organs changes. This is thought to confuse the brain, leading to space sickness. But this condition does not continue for very long. If you stay for a few days in space, your brain adjusts its interpretation of the vestibular information, so the space sickness goes away. There are individual differences in the severity of space sickness, and some people don't experience it at all. When you return to earth, you experience the effects of earth's gravity again, and thus "gravity sickness" sometimes occurs, with similar symptoms as space sickness.

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Astronauts look like their faces are bloated. Why?

Medical challenges in space: fluid shift and changes in size

The face often swells in space

Blood and other bodily fluids are pulled by gravity into the lower body. When you go to space, gravity weakens and thus fluids are no longer pulled down, resulting in a state where fluids accumulate in the upper body. This is why the face swells in space. The mucous membranes of the nose also swell, so astronauts often have congested noses. If you stay for a while in space, the fluids in your body balance out, and facial swelling typically begins to disappear after a few weeks.
Conversely, astronauts returning to earth often experience dizziness when standing up, known as orthostatic hypotension. This occurs because gravity on the earth is stronger than in space, and it is more difficult to deliver blood from the heart to the head. In space, blood can be delivered with less force, so weakening of the heart muscles may also be a cause of dizziness when standing.

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What happens to your body when you spend a long time in space?

Astronaut KANAI Norishige, training while observing the view from the Cupola ©JAXA/NASA

Bones and muscles weaken

If you stay for a long time in space, your muscles and bones will weaken, primarily in the legs and lower back. Gravity always acts on you while you're on the earth, so even if you're not really conscious of resisting gravity, you're always using the muscles of your lower body. In space, where gravity is very weak, posture can be maintained without standing on your legs, and there's no need to use your legs to move about. Muscles weaken and bone mass decreases if you stay for a long time in space.
Therefore, research is underway to verify, in space, the effects of existing drugs for preventing bone loss by astronauts. Also, to prevent weakening of muscle and bone, astronauts exercise for about two hours a day during their stay on the International Space Station (ISS).

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Is radiation more intense in space?

Astronaut FURUKAWA Satoshi with Area PADLES dosimeters in Kibo ©JAXA/FSA

In outer space, with no atmosphere, radiation is more intense and has major impacts on the human body.

The surface of the earth is enveloped by the atmosphere. This atmosphere provides the oxygen we need to breathe, and also protects organisms from the UV rays and radiation that impinge on the earth. Astronauts who stay in space, where there is almost no atmosphere, are exposed to higher energy radiation than on the earth. If a person is exposed to a lot of higher energy radiation, the risk increases that they will develop diseases such as cancer.
At JAXA, we work hard to keep space radiation exposure below a specified level, and thereby prevent astronauts from developing health problems.

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Does anything besides the body change while in space?

Expedition 48 crew enjoys a meal in the Zvezda (Russian) service module ©JAXA/NASA

People can experience intense stress living in cramped spaces

The ISS has considerably more living space than earlier spacecraft. Even so, the scope for activity is extremely limited compared to life on the earth. Astronauts develop stress before even realizing it when living and working together in a cramped space with other astronauts for a few months. The astronauts on the ISS come from different places, including Russia, America, Canada, Europe, and Japan, so factors such as language barriers and cultural differences may also lead to stress. To reduce the stress of astronauts, an environment where they can talk with family and friends while in space is provided, and space food is improved.