Astronaut Scott Kelly came back from space 2 inches taller

What happens to the human body when you haven't used your legs for almost a year when you've been floating in space instead? Well, now we know one thing is certain -- you get taller.

Astronaut Scott Kelly is back in the U.S. after spending almost a year in space -- and he came home 2 inches taller. The growth is very temporary, but the effect on the body can be long term.

"It's really not a good thing, and one of the problems is sometimes they don't fit back in their suits to come back in the planet so we have to plan for that slight growth," says Henry Ford Hospital surgeon and NASA scientist Scott Dulchavski . He's part of the team studying how space affects the human body.

"Space is hostile envirment. We see a lot of changes in the absence of gravity," he says. 

And height is one of them.

The changes in height is triggered by decompression of the spine, which happens as ligaments and muscles weaken and discs deteroiate.

"[These discs] lose fluids so they dry up, and when they dry up they're less flexible and that'a a major problem," explains Dr. Dulchavski.

He will join researchers looking at how Kelly's body now compares to his twin brother's, Mark, who stayed on Earth. As NASA looks forward to longer missions, they're studying all the mental and physical effects of space travel.

The 52-year-olds say they're proud to have served as guinea pigs for future Mars expeditions. For NASA, getting astronauts to Mars in 20 years is what this yearlong mission is all about.

"Most troubling for us right now relates to losses in bones and muscles. You don't need to use them that much when you're in space, and we try to combat that with a lot of exercise regimins," he says.

Dr. Dulchavsky says this research doesn't just help astronauts, but those of us on Earth as well because they are learning how to diagnose, prevent and treat medical conditions in a very challenging environment, which can help ultimately everyone.

While Kelly was in space, he drank nearly 200 gallons of recycled urine and sweat, collected from himself and everyone else on board. He completed 5,440 laps around the planet. Logged 143.8 million miles. Welcomed nine visiting spacecraft. Shared the place with 14 other humans, including his roommate for the long haul, Russian cosmonaut Mikhail Kornienko, who also returned to Earth.

The Associated Press contributed to this report.