Doctors raise concerns about Sunita Williams as photo of NASA astronaut emerges

Doctors have explained the reason why the returning NASA astronauts look physically different, after concerns were raised about Suni Williams' 'thin' appearance.

After a nine-month stint on the International Space Station, 59-year-old Suni and fellow Boeing Starliner pilot Butch Wilmore, 61, finally landed back on Earth earlier this week.

Considering the fact that pair were only meant to be in space for around eight days, the nine months away from home and the impromptu addition to the International Space Station crew will have come as a surprise to the pair.

It will also have had a major impact on their bodies.

As you probably already know, living outside of the confines of gravity isn't just floating around and making sure you don't spill any liquids - it can actually have a pretty significant impact on your health.

The impact of spending 286 days could be seen in the first photos of Suni after she landed off the coast of Florida, who appeared noticeably thinner and more tired than before.

Suni could be seen shaking hands and greeting various NASA officials alongside Butch and fellow ISS astronauts Alexander Gorbunov and Nick Hague in a new set of photos released by the space agency, with many appearing concerned about her 'visibly thin' wrists.

Responding to the images in an interview with MailOnline, Dr Vinay Gupta, a pulmonologist and Air Force veteran, explained that her thinner appearance was due to the absence of gravity on the ISS, which causes the body's muscles to atrophy.

"I don't think people realise that you need gravity to exercise your muscles, and if you don't have gravity, your muscles have nothing to have resistance against," he explained.

Bone density loss and muscle atrophy isn't something which would come as a shock to astronauts, as there is a wealth of research examining their relationship with gravity.

NASA previously explained that for every month spent in space, an astronaut's bone density drops by about one percent. The human heart also becomes weaker in space, as it doesn't need to work as hard to pump blood around the body.

Weight loss is also a common side effect from being in space, with Dr John Jaquish adding to the outlet: "Without gravity, you don't digest food as well. Compromising your ability to digest food is certainly going to contribute to muscle loss and bone loss on its own."

The impact of spaceflight on the human body does sound pretty traumatic, which is why astronauts will dedicate years of their lives preparing for interstellar travel. NASA also has a comprehensive aftercare protocol in place at Johnson Space Center in Houston in order to make sure astronauts are able to regain their base level of fitness.