The Anti-Aging Paradox: Why Astronauts Get "Younger" in Space (and Old on Earth).

 With regards to the historical NASA Twins Study, which pitted astronaut Scott Kelly against his look-alike twin Mark Kelly, who spent a year on Earth, here’s a quick rundown of the effects the body will experience after a year that are spent soaring above the planet.

1. Your DNA Changes (Temporarily)

The “Space Gene” Effect: This is because about 7% of Scott’s gene expression, or the turning on and off of genes, had not returned to normal even six months after he landed on Earth. This is an indication that space travel affects how our bodies respond to our genes, specifically those linked to our immune systems and DNA repair genes.

Telomere Rollercoaster: Contrary to expectations, the "caps" at the ends of chromosomes, known as telomeres, which normally get shorter as we age, actually increased dramatically during their time in space. They shrunk rapidly, even shorter than their pre-flight length, within the first 48 hours of return to Earth

2. Your Body Shape Morphs

Without the force of gravity pulling you towards the Earth’s surface, there is a huge change in the way your

Fluid Shift: Fluid that normally accumulates in the legs moves toward the head. This gives the astronauts a “puffy face” and “skinny chicken legs.”

Height Enlargement: It can add height by 2 inches (5 cm), and this happens because the spinal bone extends without the pressure of gravity acting on it. The opposite happens when one gets back into Earth’s gravity.

Muscle & Bone Loss: Despite exercising for 2+ hours per day, they experience massive bone and muscle mass loss. The reason your heart, being another muscle, actually loses size is that it has to work less hard to pump blood upwards.

3. Your Vision May Blur

Many astronauts have experienced SANS (Spaceflight Associated Neuro-Ocular Syndrome). Fluid shifts cause pressure to build up inside the skull, pressing at the back of the eyeballs. This can cause the eye to be flattened and the optic nerve to swell, resulting in farsightedness. 

4. Your Microbiome 

Adjust The bacteria in the gut change very quickly. Although the diversity of the bacteria in Scott Kelly’s gut stayed healthy (because he had a controlled diet), the type of bacteria changed substantially compared with his brother on Earth. This “space microbiome” went back to normal shortly after he returned. 

5. Cognitive Decline & Stress 

"Space Brain": Although cognitive function was maintained at a high level during the flight, the speed and accuracy in performing cognitive tasks were decreased following return to Earth. "Brain fog" continued for many months, a consequence of readaptation to Earth's gravity. Isolation: Results from psychology have found that, although performance is high, the stress of being in a confined, isolated, and noise-filled situation is a significant risk factor for missions over a period of more than a year (such as a mission to Mars).