NASA Says Space Station Astronaut Is in ‘Incredible Health’

The agency’s top medical official was responding to rumors that Suni Williams had lost an unusual amount of weight during an extended stay in orbit.

Suni Williams, a NASA astronaut currently on the International Space Station, is healthy and not suffering from any medical problems, NASA’s top medical officer said on Thursday.

The unusual pronouncement was prompted by news articles suggesting that Ms. Williams was experiencing health problems during an unplanned extended stay in orbit. That in turn set off widespread rumors on social media.

Ms. Williams, 59, addressed the issue directly on Tuesday during an interview with New England Sports Network.

“I think there’s some rumors around outside there that I’m losing weight and stuff,” she said. “No, I’m actually right at the same amount.”

Ms. Williams is one of the two astronauts whose stay at the space station was stretched from eight days to eight months because of propulsion problems with the Boeing Starliner spacecraft that took them there in June. While taking pains to insist that Ms. Williams and Butch Wilmore, the other astronaut, were not stranded, NASA decided that Starliner would return to Earth empty and that Ms. Williams and Mr. Wilmore would join the space station crew until February. They are to head home on a SpaceX Crew Dragon spacecraft instead.

A photograph that NASA released in late September showed Ms. Williams and Mr. Wilmore making pizza on the space station. Ms. Williams’s face appeared sunken and thin.

An article in The New York Post last week fueled speculation, quoting an anonymous NASA employee who claimed she had lost significant body mass.

The Post article said that Ms. Williams had been unable to consume enough calories to maintain her mass — the rigors of life in space include exercising a couple of hours a day to help maintain the astronauts’ bones — and that NASA doctors had spent a month working with her to regain mass.

In an interview, Dr. James D. Polk, the chief health and medical officer for the space agency, said that was not true.

“I’ve known Suni 20 years, and I’ll tell you, Suni looks the same to me,” he said. “She’s in incredible health right now.”

Dr. Polk said all the American astronauts on the space station were doing well. “The crew is in absolutely outstanding health,” he said. “And they’re not having any weight loss, and there’s no concern on any individual crew member.”

He added that there had not been any concerns about mass loss for any of the astronauts over the past six months.

During her video appearance on Tuesday, and another on Thursday, Ms. Williams did not appear emaciated.

She said on Tuesday that like for anyone floating in space, the shape of her body has changed. Without gravity, water within the body floats upward leaving legs shriveled and heads swollen. Weight lifting exercises have built up some muscles. “My thighs are a little bit bigger,” she said. “My butt is a little bit bigger.”

Dr. Polk said NASA would acknowledge health issues when they affect an astronaut’s ability to perform their work — if a spacewalk needs to be delayed, for instance. “We certainly will make it known if there’s a mission impact,” he said.

Even then, NASA probably would not reveal which astronaut was sick. Dr. Polk said health privacy laws applied to American astronauts in orbit in the same way that they protect Americans on the planet. “We are very strict about keeping the privacy of the astronaut,” he said.

That silence, for example, keeps a mystery on the health issue that kept a different NASA astronaut hospitalized for one night last month after returning from the space station.

Hours after the landing, NASA put out a statement that said all four astronauts who had returned to Earth in a SpaceX Crew Dragon capsule — Matthew Dominick, Michael Barratt and Jeanette Epps of NASA and Alexander Grebenkin of the Russian space agency Roscosmos — had been taken to a hospital in Pensacola, Fla., for further medical examination.

A subsequent update said Mr. Grebenkin and two of the NASA astronauts had been released while the third NASA astronaut was staying at the hospital “in stable condition under observation as a precautionary measure.” The third NASA astronaut left the hospital and returned to Houston the next day.

All three NASA astronauts appeared at a news conference earlier this month but declined to reveal who had suffered the medical issue and what the medical issue was.

“In the fullness of time, we will allow this to come out and document it,” Dr. Barratt said. “For now, medical privacy is very important to us.”

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