If it turns out that Trump’s health is less than “astonishingly excellent,” as his doctor claimed during the campaign, he’d be in good company. Nearly half the presidents have had significant illnesses while in office, according to the Los Angeles Times, and one study suggested that nearly a third of the country’s first 37 presidents—through Nixon—had a mental illness.

Some have speculated that President Reagan began showing signs of Alzheimer’s long before he left office. One study found that, with time, he began to use more nonspecific and repetitive words. Still, he emerged from his final physical shouting, “Clean bill of health!” Some researchers also think the aftereffects of anesthesia from cancer surgery hampered his decision-making abilities in the lead-up to the 1985 Iran-Contra scandal.

It’s true that recent presidents and candidates have shared their health statuses publicly, but the level of the disclosures has varied. President Obama’s last physical listed his vital statistics and noted that he chews nicotine gum on occasion.

In 1992, The New York Times described Bill Clinton as “less forthcoming about his health than any presidential nominee in the last 20 years” because, while three doctors had written letters attesting to his health, he didn’t give interviews on the topic and declined to make his doctor available to reporters.

Meanwhile, a much more detailed 2005 Times story noted that President Bush had recently lost eight pounds, and that when he “ran for 26 minutes and 20 seconds, his heart rate reached 183 beats a minute, showing no abnormalities.”

Then again, “we’ve had very sick men in office, and no one has known,” said Rose McDermott, a Brown University professor who has researched the health—or lack thereof—of past presidents. They were helped along by galling levels of secrecy.

“Grover Cleveland hid his surgery for jaw cancer, going so far as to have the operation done on a boat in New York Harbor,” said Nicole Hemmer, a media-history professor at the University of Virginia. “And of course the public was not informed of the full extent of Woodrow Wilson's debilitating stroke in 1919.”

In 1944, several doctors claimed publicly that President Roosevelt, who was running for reelection, was in good health, even as one of them privately said he doubted the president would live another four years. Indeed, he died just a few months later.

President Kennedy had a well-concealed case of Addison’s disease, a hormonal disorder, as McDermott has written. He treated it, in part, with injections of amphetamines and steroids from Max Jacobson, a doctor whose nickname was “Dr. Feelgood.” His regular endocrinologist cautioned him that Jacobson’s formulas are “not for responsible individuals who at any split second may have to decide the fate of the universe.”