American astronaut Scott Kelly did a lot while spending 340 days aboard the International Space Station. He grew plants, took some amazing pictures, conducted experiments and grew two inches.
— Scott Kelly (@StationCDRKelly) March 2, 2016
His 340 days is the longest to have been finished and part of his purpose on the International Space Station was to see how our bodies handle microgravity for extended periods of time. It is common for astronauts aboard the ISS to experience a 3% increase in height, thought to be because the spine has a chance to elongate without the stress of gravity.
His added two inches will not last though, the effect temporary. While scientist do not know exactly how long it will take for astronaut Kelly to shrink, it will probably be a few months before he is back to his normal height.
NASA has been studying this topic since 2013 with special focus on the elongating spine. These are the current studies on the topic.
Height is not the only area that scientist are focusing on, they are also looking into potential changes from extended microgravity in his vision, bones and even brian.
This type of research is integral to understand the effects of microgravity on the body so they can better prepare astronauts for for longer missions, like to Mars for instance.