Norishige Kanai, aboard the ISS, wrote on Twitter that he "had actually grown by as much as 9 cm" after a measurement in space.
However, he later said that he was mistaken. After measuring himself again and adjusting his new height increase to two cm Kanai was now 182 cm, Xinhua news agency reported on Wednesday.
"Measurement errors? But it seems to have become a serious topic. I'm terribly sorry it's fake news," Kanai tweeted.
On Tuesday Kanai had said in a tweet: "We had our bodies measured after reaching space, and wow, wow, wow, I had actually grown by as much as nine centimetres (3.5 inches)!"
"I'm a bit worried whether I'll fit in the Soyuz seat when I go back," he added.
To fit in a Soyuz seat, an astronaut should be no taller than 190 cm when standing and 99 cm when seated, according to NASA.
His words attracted 40,000 likes and 22,000 retweets. The news has drawn extraordinary international attention to his first expedition on board the ISS.
According to past studies by NASA scientists, astronauts do get taller in space by about three per cent, which means a 1.8-metre person could gain approximately five cm while in orbit.
It's known that the human spine stretches or expands while not exposed to the pull of Earth's gravity, allowing astronauts to grow taller.
Space experts pointed out the different range of growth depends on everybody's different physical responses.
Experts say the astronaut's height returns to normal after a few months back on Earth. In short, their growth is temporary.
However, it's rare for a growth of nine cm. The returning space shuttle has a height and size limit for passengers.
This is the first space mission for Kanai, who was previously a diving medical officer with the Japan Maritime Self-Defence Force.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
