Questions about Hillary Clinton's health have dominated headlines for the past 24 hours but concerns about the physical and mental health of presidential candidates -- individuals with high-stress day jobs who tend to be older -- are nothing new.
Jacob Appel, an assistant professor at Mt. Sinai Medical School who has studied the history of candidates' health, said there was no real expectation for presidents or wannabes to reveal information until 1955, when President Eisenhower had a heart attack and allowed his doctor to speak to the public about it.
Since then, Americans expect to know if their potential presidents are up for the demanding job. Most candidates have some kind of issue in their medical history and most err on the side of withholding information.
For instance, Bob Dole, John Kerry and John McCain were all cancer survivors who had been wounded in combat. All three are still active: Kerry is secretary of state, McCain is running for reelection in the Senate in Arizona, and Dole, at 93, attended the Republican National Convention and still gives interviews.
"The vast majority of people in their 50s, 60s, and 70s have a long laundry list of illnesses that might affect them every day, but are perfectly fit people" to do their jobs, noted Appel. "You want to ask yourself not if a candidate has an illness, but if they have an illness that would impair their ability to serve out their term or to govern effectively."
Both Clinton and Donald Trump would be among the oldest presidents ever elected, so the scrutiny is especially intense. To put Hillary Clinton's recent pneumonia diagnosis in context, here's a brief history of presidential candidates' physical health:
Barack Obama in 2008 - Obama was an unusually young candidate with a relatively spotless record, but still faced questions about his smoking habit and past drug use.
John McCain in 2008 - McCain set the standard for medical disclosure, according to Appel, making available to reporters 1,173 pages of health records. He faced pressure to do given his age (he was 72) and three battles with cancer.
John Kerry in 2004 - Kerry left the presidential campaign trail in early 2003 to receive treatment for prostate cancer.
Bob Dole in 1996 - Dole was diagnosed with and treated for prostate cancer before he ran for president in 1996 and has spoken publicly about the disease. Doubts about his stamina were raised when Dole fell off a stage during a campaign event.
Paul Tsongas in 1992 - Sen. Paul Tsongas, who ran for president in 1992, is "the most glaring modern example" of politicians obscuring health issues from the public, said Appel. During the campaign, Tsongas and his doctors suggested he had overcome a previously diagnosed case of non-Hodgkin's lymphoma. He died five years later of complications from the disease at 55.
Bill Clinton in 1992 - Clinton's often hoarse voice led to perennial questions about his health, as did his weight, which was mocked by Saturday Night Live.
George H.W. Bush in 1988 and 1992 - When president Bush suffered from a thyroid problem and irregular heartbeat in 1991, critics warned Vice President Dan Quayle -- who was widely seen as under-qualified -- was a "heartbeat away from the presidency."
Ronald Reagan in 1980 and 984 - Reagan was and remains the oldest president elected and faced questions about his age. When he ran for reelection in 1984, he defused tension around his health in a debate against Democrat Walter Mondale, "I am not going to exploit, for political purposes, my opponent's youth and inexperience." But his health deteriorated as he was in office and he was later diagnosed with Alzheimer's disease.
Thomas Eagleton in 1972 - Eagleton was forced to withdraw from the vice presidential ticket under George McGovern and replaced by Sargent Shriver after it was revealed that he had been given shock therapy and seen a therapist.
Lyndon Johnson and Barry Goldwater - The 1964 election has many parallels to 2016, including concerns about President Johnson's health after he suffered a heart attack and allegations -- later proved unfounded -- that Republican Barry Goldwater was mentally ill.
Before Eisenhower's example, presidents routinely hid their health woes from the public.
The press famously conspired with Franklin Delano Roosevelt to cover up his paralysis. And as Roosevelt campaigned for his fourth tern in 1944, his doctor issued a report saying president's health was "satisfactory" -- Roosevelt died the next spring.
President Grover Cleveland had a surgeon sneak onto a friend's yacht so he could have surgery to remove a tumor and disguise it as vacation. Woodrow Wilson had a more major stroke that his wife hid from the public as she essentially ran the country in secret. And John F. Kennedy, despite his youthful image, quietly suffered from a number of ailments.
A group of psychiatrists in 2006 concluded that 18 of the nation's 37 first presidents would meet modern criteria for psychiatric disorders -- mostly depression, anxiety, alcoholism, or bipolar disorder. And in 10 cases, they claimed the disorder was present while the president was in office. .