Does living in space change how genes work?

More than 200 researchers are studying the world’s only twin astronauts Scott and Mark Kelly inside out. Literally. Under scrutiny is their physiology, immune system, eyesight, bone formation, DNA, gut bacteria, the works.

Nasa took up a project to study the impact of living in space on humans. This experiment was possible because Scott and Mark Kelly are identical twins. Scott spent almost a year on the International Space Station. The aim was to reveal the long-term effects of space travel on the human body and mind, and prepare for a three-year mission to Mars. Most astronauts spend 6 months in space, but Scott spent 340 days — the single longest space mission ever.

Scott's identical brother Mark, a retired astronaut, remained on Earth as a control subject. Both brothers’ physical and mental health were mapped. Most of Scott’s physical changes proved to be temporary responses to the low-gravity, low oxygen environment of space.

He was 2 inches taller on his return. His body mass had decreased. Gut bacteria were completely different. One of the surprising findings is that Kelly’s chromosomes grew longer.

However he shrunk back to his old height over time. But genes involved in bone formation, oxygen deprivation, immune system responses and DNA repair remained transformed. Researchers said living in space causes ‘stress’ that activates an immune response. ‘Unpleasant aspects’ of being in space can start off changes in a cell’s biological pathways. It can trigger cell degradation and change cell function.

This is how scientists are explaining the findings. Living in space altered his genetic expression, and not code, as was initially reported by some. Expression levels reflect whether genes are turned on or turned off. Most cells are genetically identical, but genes are expressed at different levels, such as for the immune system and bone formation.

Nasa said only 7% of gene expression that changed during Kelly’s spaceflight had not returned to preflight after six months on Earth.

Sources: Nasa, Time, NatGeo