Why Astronauts Grow Up to Five Centimeters When They Go to Space

Traveling outside the Earth causes a loss of muscle mass, visual problems, and circadian rhythm disorders.

A Japanese astronaut, Norishige Kanai, announced on Tuesday that he had grown nine centimeters in space during his three weeks on the International Space Station (ISS). "I'm a little worried about whether I'll enter the Soyuz space seat when I return," he said on his Twitter handle. This ship is the one that takes astronauts from Earth to the ISS and vice versa, and their seats have a height limit. But this Wednesday, after the news went around the world, Kanai apologized for an error in the measurement. It really has only grown two centimeters.

Astronauts grow in space between two and five centimeters. This is due to the absence of gravity, which causes the vertebrae to separate and the spine to expand. But when they return to Earth, in a short time, they return to their original height. "The discs are like sponges," explains the founder and first director of the Museu de la Ciència de Barcelona, Rafael Clemente. This industrial engineer and specialist in astrophysics said that the backbone does not extend unlimitedly. It does not matter if you are in space for a month or a year, there will come a time when you will not grow anymore.

Since human beings arrived in space more than 50 years ago, several medical studies have been conducted to determine how it affects the human body on leaving the Earth. Scott Kelly was the first ever American to spend almost a year in space aboard the International Space Station. NASA studied how the trip affected his health by comparing it to that of his twin brother, who stayed on Earth.

One of the most damaging effects of traveling to space is that you lose a lot of calcium. There, you float and moving requires much less effort. While an elderly person on Earth can lose 1% of bone mass per year, in space, that amount is volatilized in a month. In addition to that, inside the capsule, astronauts are not exposed to any sun, an essential source of vitamin D. "What happens is very similar to what happens to older people who are bedridden. They suffer from osteoporosis or loss of calcium ", underlines Clemente. To alleviate this problem, they have a very intense exercise program throughout the day. They spend hours on the stationary bike or in the weightlifting simulator.