Democratic presidental nominee former Secretary of State Hillary Clinton gets into a van as she leaves the home of her daughter Chelsea Clinton on September 11, 2016 in New York City.

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.