In December, Donald Trump’s physician claimed that Trump would “unequivocally” be “the healthiest individual ever elected to the presidency.” His statement, full of non-medical, but positively Trumpian descriptions of the Republican presidential candidate’s physical excellence, resurfaced recently after right wing circles claimed that rival Hillary Clinton is physically and mentally unfit for office.

On Friday, Dr. Harold Bornstein told NBC News that he stands by his claims, adding that he wrote the letter in five minutes while a limo sent by Trump was waiting. “I like that sentence to be quite honest with you and all the rest of them are either sick or dead,” Bornstein said, referring to his statement that Trump would be the healthiest president ever. Other doctors have responded with skepticism, with one describing the claim as ”patently ludicrous” to science journal STAT news.

Trump abstains from alcohol and tobacco, which is important for physical health. He plays golf. But he would be the oldest president elected to office, at 70 on Election Day. He works around the clock and boasts he only sleeps three or four hours per night—the kind of stressful lifestyle that has repeatedly been proven to take a toll on your health. Trump also loves fast food. You don’t have to look far back in presidential history to find presumably healthier individuals: The much younger Obama with his daily exercise and strict snacking policy, as well as George W. Bush with a marathon under his belt, could be challengers to Bornstein’s claims.

And is it even possible to say which president is or was “the healthiest?”

The history of presidential health is murky. We simply don’t have medical reports from presidents that date beyond the last several decades. Many presidents kept their health under wraps, hiding their true conditions: Calvin Coolidge was secretly depressed; Woodrow Wilson suffered a paralyzing stroke while president. Because we have so little information on the topic, presidential historian H.W. Brands described Bornstein’s statement as ”utterly irresponsible” in an email to Quartz.

Health can be much harder to compare than policy positions. Both Bush and Obama were generally in excellent health according to their annual medical reports, but Bush suffered minor sports-related injuries and mild hearing loss and Obama has a history of smoking. Obama may have a resting heart rate of 56 beats-per-minute, but how does that rank him against Theodore Roosevelt, who practiced martial arts in the White House and was an actual cowboy? Or John Quincy Adams, who swam naked in the Potomac river every day and lived more than 30 years longer than his peers?