President Donald Trump's officials and advisers are "irritated" by chatter about the 79-year-old chief executive's health for a surprising reason, according to one of his biographers.

The White House has been forced to comment on odd bruising on the president's left hand and tried to hide his swollen ankles in official Oval Office photos, and author Michael Wolff told the Daily Beast podcast "Inside Trump’s Head" that insiders are panicking behind the scenes.

“The only thing that I’m hearing about his health is everyone is irritated that people are focusing on his health—I mean, the people around him,” Wolff said. “Because — and actually this makes some sense — what they see is Donald Trump always moving ahead, a man who doesn’t stop, inexhaustible. On the other hand, they acknowledge one day he will just go over.”

“They say that?” Coles replied.

“Yeah,” Wolff agreed. “The idea that he will fade, that he will become sick, that he will be mortal in that way that we all are — they actually don’t accept he will stop at one point and that will be it.”

The White House was forced to reveal Trump has chronic venous insufficiency, which can cause swollen legs, and the president has been dogged by speculation about his mental state – including as recently as Tuesday, when California Gov. Gavin Newsom suggested he had dementia after repeating false claims about releasing water to assist with Los Angeles wildfires.

“President Trump is the most energetic and transformative president in history, and he works nonstop on behalf of the American people,” White House spokesperson Davis Ingle told the Daily Beast. “Today’s three hour marathon long Cabinet meeting that was open to the press and the American people prove exactly that.”