The image most people had of John F. Kennedy was one of youth and vitality. And, that was on purpose. JFK in fact lived in near-constant pain, but his poor health was kept a closely guarded secret for fear of damaging his political career. He had allergies, stomach troubles and suffered from chronic back pain, which was aggravated by his World War II service and required numerous surgeries. The back injury allegedly happened in 1937 while he was a student at Harvard, and it initially disqualified him from military service (his father later used his connections to get JFK into the Naval Reserve).

He’d been ill before the injury, too. As a child he suffered from gastrointestinal issues, which were later diagnosed as Addison’s disease, an endocrine disorder. In a strange twist of fate, one of the symptoms of Addison’s—as well as a symptom of the steroids used to treat it—is hyperpigmentation, which may be responsible for JFK’s perpetual “tan,” something viewers of his televised debate with Richard Nixon definitely noted.

Today most Americans are aware that our longest serving president suffered from the effects of polio and relied on a wheelchair for mobility. However, during his tenure as commander in chief, FDR was able to hide the severity of his condition to an almost unimaginable extent by today’s standards. He was diagnosed with polio in 1921, when he was 39 years old. This was unusual because most polio victims at the time were children under the age of four.

FDR worked tirelessly to rehabilitate his body in the years after contracting polio. As he’d been rendered a paraplegic, he used a specially designed wheelchair to get around most of the time. While president, he wanted to project strength and virility, and so devised a way to “walk” during public appearances. It involved wearing leg braces, using a cane, and utilizing the arm of his son or a trusted advisor. Additionally, he asked the press to refrain from photographing him walking, or being transferred from his car, and the Secret Service was charged with interfering with those who attempted to capture images that might portray the president as “weak.”

When Woodrow Wilson was inaugurated in 1913, the well-known military physician Silas Weir Mitchell predicted he wouldn’t complete his first term due to his health. This prediction turned out to be false, but Wilson did have his share of health scares while in office. In 1919, a doctor noted that Wilson’s mouth was drooping on one end, a classic sign of minor stroke. It only deteriorated from there, and in October the president awoke to find himself partially paralyzed. His wife Edith sprung into action, both protecting his reputation and maintaining calm in the administration. She essentially acted as the president, and the country was kept in the dark about Wilson’s true condition until after his term ended in 1921.

Why didn’t Wilson’s vice president, Thomas Marshall, take over? In 1919, the rules of presidential succession in the case of injury weren’t clearly defined. The 25th amendment wasn’t ratified until 1967, and so Wilson’s administration was operating under Article 2 of the constitution, which provided for a vice presidential takeover in the case of “death, resignation, or inability to discharge the powers and duties of the said office.” Wilson wasn’t dead and was unwilling to resign under these circumstances, so the vice president refused to assume the presidency unless Congress passed a resolution declaring the office vacant.

Dwight D. Eisenhower on Richard Nixon contributions as his vice president: 'If you give me a week, I might think of one. I don’t remember.'

Before Richard Nixon was our infamous 37th president, he was Dwight D. Eisenhower’s veep. Judging by the remark Eisenhower made at a 1960 presidential news conference, they didn’t get along so well.

Time correspondent Charles H. Mohr was asking Dwight about what Nixon actually did in his administration, and was getting some pushback. Dwight said Nixon “was not a part of decision-making,” and Mohr countered that he must be doing something.

“We understand that the power of decision is entirely yours, Mr. President,” he said. “I just wondered if you could give us an example of a major idea of his that you had adopted in that role, as the decider and final—”

That was when Dwight cut him off, saying he’d need those seven days to think of one.

Born February 6, 1911, the nation’s 40th president was 77 years and 349 days old at the completion of his second term in January 1989. While campaigning in 1980, Reagan tried to put to rest questions about his age by pledging that he would resign if the White House physician ever detected signs of mental deterioration.

Once in office, Reagan proved to be remarkably resilient, and survived an assassination attempt in 1981, as well as surgery in 1985 to remove a cancerous polyp in his large intestine. Reagan always seemed the picture of robust health, in part because he exercised regularly with weights and enjoyed horseback riding and performing manual labor at his ranch in California. Reagan was able to brush aside concerns about age with humor, once joking during a 1984 debate that “I am not going to exploit, for political purposes, my opponent’s youth and inexperience.”