Look a little closer
Astronauts become taller in orbit without suddenly growing new bone. In microgravity, the load pressing down the body nearly disappears, allowing spinal curves and tissues between vertebrae to decompress.
On Earth, standing and walking place an axial load from the head through the pelvis. Water-rich intervertebral discs compress like cushions, while the spine's natural curves help carry body weight.
Aboard a space station, feet do not continuously bear against a floor, so this compression drops sharply. Discs expand and the spine straightens slightly, increasing body length.
NASA says height can increase by as much as about three percent during long missions. That maximum would be roughly five centimeters for a 180-centimeter person, but changes vary and not everyone reaches it.
This is not permanent growth. After return to gravity, the spine readapts and height generally returns to its preflight value. It resembles being slightly taller after lying down overnight, but the orbital effect is larger.
Extra height does not mean improved health. Microgravity weakens muscle and bone, and researchers study back discomfort and disc risk. Astronauts exercise while teams monitor spinal changes with tools including ultrasound.
