Space travel: what effects on the human body?

When an astronaut goes into space, they enter microgravity after traveling 100 km from Earth. There, the effects of gravity have practically disappeared, but not completely. There remains a very weak residual gravity inside orbiting spacecraft. The first effect? ​​"All the blood from the lower part of the body rises to the upper part," explains Guillemette Gauquelin-Koch.

The heart then has to manage a blood volume much greater than that on Earth. This causes the heart to dilate and an increase in cardiac output, which eventually passes, as the body manages to adapt by causing a decrease in plasma volume. "But back on Earth, when suddenly exposed to gravity, astronauts experience orthostatic hypotension—a drop in blood pressure when standing—because the cardiovascular system has forgotten how to fight gravity," the specialist explains.

Space sickness

The astronauts then enter the station, and perception problems arise. "They arrive in a place where they can't walk. However, the legs are involved in our perception of space, and there, they are no longer useful. And above all, the vestibular system is immediately disrupted. This disruption is responsible, in particular, for space sickness," the expert continues. The symptoms that affect many astronauts are nausea, vomiting, dizziness, fatigue, headaches, and balance problems. They fade after a few days or even a week.

Accelerated aging

In the long term, the major effect is accelerated aging. "Because 2 hours a day on a treadmill is not enough! Astronauts' bodies age prematurely due to the lack of physical exercise!" This causes changes in bone, muscle, metabolic, and cardiac function. "We realized that in astronauts, lipids are stored in places where they shouldn't be." Microgravity and lack of activity promote the deposition of lipids in organs not intended for this, in the liver and muscles. This change in fat storage can be responsible for obesity, type 2 diabetes, fatty liver, etc. "But it's important to know that this is reversible. Once they return to Earth, an astronaut can get back on their feet fairly quickly," continues Guillemette Gauquelin-Koch.

SANS syndrome

Another consequence of space travel is SANS, or Spaceflight Associated Neuro-ocular Syndrome. "Astronauts report seeing less well after returning from spaceflight. This is thought to be due to a buildup of cerebrospinal fluid in the upper body and increased eye pressure."

Weakening of the immune system

A weakened immune system is also observed in astronauts. "In space, isolation remains a significant stress factor. And we know that chronic stress can influence immune defenses, as can inactivity. Circadian rhythms are also significantly affected, and sleep with them. Circling the Earth means 45 minutes of night / 45 minutes of day. This stress may not be felt by astronauts, but their bodies do."

Traveling to Mars soon?

"As long as it's a flight of 6 months to 1 year, astronauts can handle it. They're trained for it and then recover quickly. However, we've realized that for bones, recovery is probably more complicated. For example, after a 6-month flight, bone density still hasn't returned 18 months later. This can cause fractures or kidney stones, because calcium has to be eliminated through urine." A solution to counter bone loss will have to be found before a trip to Mars can be considered.

For Guillemette Gauquelin-Koch, from a strictly human perspective, aside from bone loss, the psychological aspect and radioactivity remain the major obstacles to the Martian adventure. "Going to Mars is at least an 8-month flight each way, without Earth in sight and with telecommunications that are no longer as efficient, 15 minutes to send a question, 15 minutes to send the answer. Astronauts will have to know how to do everything without ever being able to rely on Earth. As for the radiation level, it will be much higher than during trips to the ISS." Currently, astronauts are not said to be affected by radiation doses.

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