Astronauts shrink when they return to Earth: This and other facts

As Sunita Williams and Barry Wilmore are expected to return on March 19/20, a lot is being discussed about their health as the body undergoes several changes during a prolonged stay under microgravity.
Space travel is one of the most fascinating achievements of humanity, pushing the limits of human endurance, technology, and our understanding of the universe. But did you know that astronauts actually shrink when they return to Earth? This is just one of the many strange effects space has on the human body. From changes in bone density to altered vision and even the psychological impact of isolation, space travel presents a variety of challenges.

One of the most surprising changes astronauts experience is a loss in height after returning from space. While in microgravity, astronauts actually grow taller—by up to 5 cm (2 inches)—as their spine elongates. The lack of gravity allows the vertebrae in the spinal column to expand. However, once they return to Earth, gravity compresses their spine back to its normal length, making them shrink back to their original height.

On Earth, our bones and muscles stay strong because they constantly work against gravity. In space, where there is little to no gravity, astronauts’ bones and muscles start to weaken. They can lose 1-2% of bone mass per month, making them prone to fractures when they return to Earth. This condition is similar to osteoporosis.

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Another major effect of space travel is changes in astronauts’ eyesight. Many astronauts report worsening vision after spending months in space. This condition, known as Spaceflight-Associated Neuro-ocular Syndrome (SANS), happens because fluid shifts in microgravity cause increased pressure inside the skull, affecting the shape of the eyeball.​

Ever noticed how food tastes different when you have a cold? Something similar happens to astronauts in space. The fluid shift in their bodies due to microgravity makes their sinuses swell, leading to a stuffy-nose sensation. This dulls their sense of taste, making food seem bland.

Despite the hardships of space travel, astronauts also experience something profound—the Overview Effect. This is a shift in perspective that occurs when they see Earth from space. Many astronauts describe feeling an overwhelming sense of unity, realizing how fragile and interconnected our planet is.



This experience has inspired many astronauts to become advocates for environmental conservation and global cooperation upon returning to Earth. The late astronaut Edgar Mitchell, who walked on the Moon, once said, "You develop an instant global consciousness, a people orientation, an intense dissatisfaction with the state of the world, and a compulsion to do something about it."

Tears behave strangely in space due to microgravity. On Earth, gravity pulls tears down when we cry. In space, however, tears don’t fall—they form little balls of liquid that stick to the astronaut’s face. This makes crying an unusual and uncomfortable experience.

Prolonged exposure to microgravity also affects the heart. Studies have found that astronauts’ hearts become more spherical in space, likely because the heart doesn’t have to work as hard to pump blood in microgravity. While this change reverses upon returning to Earth, it raises concerns for long-duration space missions.

Perhaps one of the most surprising discoveries about space travel is its impact on human genetics. NASA’s famous Twin Study, conducted on astronaut Scott Kelly and his identical twin Mark Kelly (who stayed on Earth), revealed that long-term space exposure can lead to gene expression changes, affecting immune function, bone growth, and even DNA repair mechanisms.
Space travel affects telomeres—the protective caps on the ends of chromosomes. Scott Kelly’s telomeres lengthened while in space but returned to normal after he came back to Earth. This raises fascinating questions about how space travel affects aging and longevity.