John F. Kennedy, who was just 43 when elected president in 1960, was the youngest person ever elected to the Oval Office. Outwardly, he seemed like the picture of youthful vitality and health, but the American public didn’t know that beneath the young president’s robust image, he was someone who struggled with numerous health issues.

Despite JFK’s slim, athletic-looking physique and skill at pastimes such as golf and sailing, he contended with spinal problems and osteoporosis that left him in chronic pain. He was also afflicted with Addison’s disease, a condition in which damaged adrenal glands don’t produce enough hormones, causing fatigue, digestive difficulties and low blood pressure. And he experienced severe allergies and urinary tract infections.

As historian Robert Dallek discovered when studying his medical records years later, Kennedy took as many as 12 different medications at once. He used demerol and methadone for pain, barbiturates to help him sleep, an amphetamine, thyroid hormone, and an anti-anxiety medication, and injections of gamma globulins to fight infections, among other prescriptions.

“In actuality, he had the most complex medical history of anyone to occupy the White House,” Dr. Lee R. Mandel wrote in 2009 in Annals of Internal Medicine.

But hardly anyone found out, because Kennedy kept the extent of his health problems a carefully guarded secret, and instead worked to craft an image of good health—and he encouraged Americans to prioritize their health as well. He wrote an article for Sports Illustrated warning that Americans were too soft, and created the President’s Council on Physical Fitness to encourage both children and adults to exercise more.

“He was always careful to get a suntan, either with a sunlamp or sunshine,” notes Historian Barbara A. Perry, director of Presidential Studies at the University of Virginia’s Miller Center, and an author of numerous books, including a biography of JFK’s mother Rose Kennedy.

One reason that Kennedy was able to conceal his health problems was that he didn’t let them keep him from doing the job.

“Although Kennedy took a generous amount of drugs, it is not clear that it negatively affected his performance in office, even during the Cuban Missile Crisis,” says John R. Vile, a political science professor and dean of the University Honors College at Middle Tennessee State University.

Kennedy’s health problems began early in life. A few months before his third birthday, he developed a serious case of scarlet fever, an infectious bacterial disease that in the days before antibiotics was potentially life-threatening, and spent a month in the hospital with his father Joseph Kennedy Sr., at his side. “Joe senior prayed that if God would save his little son, he would make donations around the town, and he did,” Perry says.

Though he survived, JFK’s health after that was always fragile. The future president was plagued throughout childhood and adolescence by nausea, joint pain, headaches, diarrhea and other woes, and was hospitalized several times. At one point, his family sent him to the Mayo Clinic in Minnesota, where he was diagnosed with colitis, an inflammation of the colon. In reality, Kennedy may have been showing early signs of a malfunctioning immune system that was attacking his own body, and eventually led to his developing Addison’s disease.

“The family joke was that if a mosquito bit Jack Kennedy, the mosquito would die, because apparently there was something in poor Jack Kennedy’s bloodstream,” Perry says.

After graduating from prep school, he had to drop out of both the London School of Economics and Princeton University due to illness before recovering enough to enroll at Harvard. Remarkably, despite frequent bouts of ill health that landed him in the infirmary, he played on the freshman football team and competed for two seasons on the varsity swimming squad.

Kennedy already had problems with his spine when he enlisted in the U.S. Navy, where he got in despite failing the physical, thanks to his father’s political connections, according to a 2017 article in the journal JNS Spine. In 1943, the patrol boat that JFK commanded in the South Pacific was struck by a Japanese destroyer in August 1943. Kennedy survived the disaster and led most of his crew to eventual safety, a record of heroism that later helped his political career, but his back worsened as a result. The following year, he had back surgery for the first time.

After the war, Kennedy’s ill health continued. During his successful run for a Massachusetts seat in the U.S. House, his back was so bad that he began wearing a brace, and followed a regimen of daily hot baths and massage to manage the pain. Once elected, Kennedy had a valet who helped him up the stairs in his Georgetown home, according to Perry. The servant “would help him get his shoes on and tie them, because he couldn’t bend over,” she says.

After the Congressman collapsed while on a visit to England in 1947, a doctor there diagnosed Addison's disease, and told one of JFK’s friends that he might be dead in a year. Kennedy passed off the illness as a recurrence of his wartime malaria, but when he got back to Boston, an endocrinologist began treating him for Addison’s by implanting pellets of synthetic adrenal hormone under his skin, according to Mandel’s article. By 1950, when cortisone was available in oral form, he began taking 25 milligrams each day as well.

By the time that Kennedy ran for the U.S. Senate in 1952, he had so much trouble with his back that when he attended afternoon teas in Massachusetts towns and cities to connect with women voters, “he’d be standing on crutches, because he literally couldn’t stand up without leaning on them,” Perry says. His pain and difficulties with mobility grew so severe that he had to endure three more back surgeries during the 1950s. After one operation, he developed an infection that nearly killed him, according to Perry.

Afterward, “I’m sure he was depressed, just lying in bed and not being able to move, and being in constant pain,” Perry says. But Kennedy didn’t succumb to despair. Instead, during his long recovery, he wrote the nonfiction bestseller Profiles in Courage.

Meanwhile, Kennedy continued to struggle with Addison’s disease. When Dr. Janet G. Travell, who would become JFK’s White House physician, first met him at her office in New York City in May 1955, she later recalled that he had difficulty climbing a couple of steps to her door. “He could walk on the level, putting his weight on his right leg, but he couldn’t step up or down a step with his right foot,” she told presidential historian Theodore C. Sorensen years later.

Despite his health struggles, Kennedy was determined to keep rising in politics—but he knew that his problems were likely to end his career if they ever became public. According to Dallek’s biography An Unfinished Life: John F. Kennedy, 1917 – 1963, JFK kept his health problems secret from everyone except for his doctors, his wife Jackie, and his brother Bobby. Even his secretary Evelyn Lincoln, who was responsible for making sure that he took his medication, may not have known what it was for, Dallek writes.

Nevertheless, word did leak out. When Kennedy ran for president in 1960, his Democratic rival Senator Lyndon Johnson of Texas began raising questions about JFK’s health, leading the Kennedy campaign to release a statement denying that he had Addison’s disease and describing his health as “excellent.” In the age before social media and 24-7 cable news channels, the rumors about Kennedy’s health didn’t resonate widely among the public.

“It wasn’t enough to prevent him from getting the nomination,” Perry notes. He went on to defeat GOP candidate Richard Nixon, helped by a historic  TV debate in which Kennedy  appeared healthier than his rival, who had been sick from a knee infection and a case of the flu that left him looking pale.

Kennedy’s health remained secret in the White House. During a tree-planting ceremony in Canada in May 1961, he aggravated his back. Perry believes the pain—and JFK’s use of amphetamines—may have been a factor in his performance in a summit meeting with Soviet leader Nikita Khrushchev the following month. (Kennedy later told a New York Times reporter “He just beat the hell out of me” about his meeting with Krushchev.)

After returning from that disastrous experience, he began to exercise diligently to manage his back pain, as Travell recalled in her interview with Sorensen. He swam each day in the White House pool just before lunch, and returned for a second swim in the evening, when he also did a regimen of exercises for his legs and back, designed for him by Dr. Hans Kraus, founder of the specialty of sports medicine. The workout “did him a great deal of good,” Travell said.

By the October 1962 Cuban Missile Crisis, Kennedy was able to power through his daily discomfort and the effects of the drug regimen, and successfully resolve a crisis that could have led to war. “It clearly didn’t block his rational judgment powers,” Perry says. “That’s important, I think, to know.”

“One of the factors that gave Kennedy the appearance of health was his youthful appearance and his witty repartee with reporters at press conferences,” Vile notes. Nevertheless, some reporters apparently did hear rumors about the President’s health. But when they approached White House Press Secretary Pierre Salinger, “he said, well, let me ask you a question. Do you think he is not performing in the Presidency, and isn’t up to the task of doing what he needs?” Perry explains.

But Kennedy’s back problems may have played a role in making him more vulnerable to assassination by Lee Harvey Oswald in Dallas in November 1963, according to one of the physicians who treated Kennedy in the emergency room at Parkland Hospital that day. In 2013, Dr. Kenneth Salyer told CBS News that the stiff back brace that Kennedy wore kept him erect, even after he was hit in the shoulder and neck. Sayler argues that gave Oswald a chance to fire another shot, which struck Kennedy in the head and inflicted a fatal injury.