In 2010, Robert F. Kennedy Jr. was suffering from memory loss and brain fog so severe that a friend began to fear he might have a brain tumor. Mr. Kennedy said he had consulted many of the country's top neurologists, many of whom had treated or spoken to his uncle, Senator Edward M. Kennedy, before his death the previous year from brain cancer.
Several doctors noticed a dark spot on the young Mr. Kennedy's brain scans and concluded that he had a tumor, he said in a 2012 deposition reviewed by The New York Times. Mr. Kennedy was immediately scheduled for surgery at Duke University Medical Center by the same surgeon who had operated on his uncle, he said.
As he was packing for the trip, he said, he received a call from a doctor at NewYork-Presbyterian Hospital who had a different opinion: Mr. Kennedy, he said, had a dead parasite in his head.
The doctor believed the abnormality seen in his scans “was caused by a worm that entered my brain and ate part of it and then died,” Mr. Kennedy said in the deposition.
Now an independent presidential candidate, the 70-year-old Kennedy has described his athleticism and relative youth as an advantage over the two oldest people to ever seek the White House: President Biden, 81, and former President Donald J. Trump, 77. Mr. Kennedy secured places on the ballot in Utah, Michigan, Hawaii and, according to his campaign, California and Delaware. His intense efforts to gain entry into more states could put him in a position to overturn the election.
He went to great lengths to appear healthy, skiing with a professional snowboarder and Olympic gold medalist who called him a “ripper” as they raced down the mountain. A camera crew stood beside him as he lifted weights, shirtless, at an outdoor gym in Venice Beach.
However, over the years, he has faced serious health problems, some of which were previously hidden, including the apparent parasite.
For decades, Mr. Kennedy suffered from atrial fibrillation, a common heartbeat abnormality that increases the risk of stroke or heart failure. He has been hospitalized at least four times for episodes, although in an interview with the Times this winter, he said he had not had an accident in more than a decade and believed the condition had disappeared.
Around the same time he learned about the parasite, he said, he was also diagnosed with mercury poisoning, most likely due to ingesting too many fish containing the dangerous heavy metal, which can cause serious neurological problems.
“I clearly have cognitive issues,” he said in the 2012 deposition. “I have short-term memory loss and I have long-term memory loss that affects me.”
In the interview with The Times, he said he had recovered from memory loss and fogginess and had had no side effects from the parasite, which he said had not required treatment. Last week, asked whether any of Mr. Kennedy's health problems could compromise his eligibility for the presidency, Stefanie Spear, a spokeswoman for Kennedy's campaign, told the Times: “That's a hilarious suggestion, given the competition.”
The campaign declined to provide his medical records to the Times. Neither President Biden nor Mr. Trump have released medical records this election cycle. However, the White House released a six-page health summary for President Biden in February. Mr. Trump released a three-paragraph statement from his doctor in November.
Doctors who have treated parasitic infections and mercury poisoning have said that both conditions can sometimes permanently damage brain function, but patients can also experience temporary symptoms and make a full recovery.
Some of Mr. Kennedy's health problems were revealed in the 2012 deposition he gave during divorce proceedings from his second wife, Mary Richardson Kennedy. At the time, Mr. Kennedy claimed that his earning power had been diminished by his cognitive problems.
Mr. Kennedy provided more details, including about the apparent parasite, in the telephone interview with the Times, conducted when he was about to contest his first state ballot. His campaign declined to answer follow-up questions.
In the days after the 2010 call from NewYork-Presbyterian, Mr. Kennedy said in the interview, he underwent a series of tests. Scans taken over several weeks showed no changes in the area of his brain, he said.
Doctors eventually concluded that the cyst seen on the scans contained the remains of a parasite. Mr Kennedy said he did not know the type of parasite or where he might have contracted it, although he suspected it may have been during travel through South Asia.
Several infectious disease experts and neurosurgeons said in separate interviews with the Times that, based on what Mr. Kennedy described, they believed it was likely a pork tapeworm larva. The doctors did not treat Mr. Kennedy and spoke in general.
Dr. Clinton White, a professor of infectious diseases at the University of Texas Medical Branch in Galveston, said the microscopic tapeworm eggs are sticky and transfer easily from one person to another. Once hatched, the larvae can travel in the bloodstream, he said, “and end up in all kinds of tissues.”
While it is impossible to know, he added that it is unlikely that a parasite would eat part of the brain, as Mr. Kennedy described. Rather, Dr. White said, it survives on nutrients from the body. Unlike tapeworm larvae in the intestine, those in the brain remain relatively small, about a third of an inch.
Some tapeworm larvae can live in the human brain for years without causing problems. Others can cause damage, often when they begin to die, causing inflammation. The most common symptoms are seizures, headache and dizziness.
According to the journal Emerging Infectious Diseases, there are approximately 2,000 hospital admissions in the United States each year for the condition known as neurocysticercosis.
Scott Gardner, curator of the Manter Laboratory for Parasitology at the University of Nebraska-Lincoln, said that once a worm is in the brain, the cells calcify around it. “And you will basically almost have a tumor that will be there forever. It's not going anywhere.”
Dr. Gardner said it is possible that a worm could cause memory loss. However, severe memory loss is more often associated with another health problem that Mr. Kennedy said he had at the time: mercury poisoning.
Mr Kennedy said he was then living on a diet high in predatory fish, particularly tuna and perch, both known to have high levels of mercury. In the interview with The Times, he said he experienced “severe brain fog” and had difficulty regaining words. Mr. Kennedy, an environmental lawyer who has railed against the dangers of mercury contamination in fish from coal-fired power plants, had his blood tested.
He said tests showed his mercury levels were 10 times what the Environmental Protection Agency considers safe.
At the time, Mr. Kennedy had also been on a crusade against thimerosal, a mercury-containing preservative used in some vaccines, for a few years. He is a longtime vaccine skeptic and has falsely linked childhood vaccinations to the rise of autism, as well as other medical conditions.
In the interview, Mr Kennedy said he was certain his diet had caused the poisoning. “I loved tuna sandwiches. I ate them all the time,” she said.
The Times described Mr. Kennedy's symptoms to Elsie Sunderland, a Harvard environmental chemist who did not speak to Mr. Kennedy and responded generally about the condition.
He said the mercury levels described by Mr Kennedy were high, but not surprising for someone consuming that amount and type of fish.
Mr Kennedy said he made changes after these two health problems, including sleeping more, traveling less and reducing his fish consumption.
He also underwent chelation therapy, a treatment that binds to metals in the body so they can be excreted. It is generally given to people contaminated with metals, such as lead and zinc, in industrial accidents. Dr. Sunderland said that when mercury poisoning is clearly diet-related, she would simply recommend the person stop eating fish. But another doctor who spoke to the Times said he would recommend chelation therapy for the levels Mr Kennedy said he had.
Mr. Kennedy's heart problem began in college, he said, when he began beating out of sync.
In 2001, he was admitted to a Seattle hospital while in town to give a speech, according to news reports. He was treated and released the next day. He was hospitalized at least three more times between September 2011 and early 2012, including once in Los Angeles, he said in the deposition. During that visit, he said, doctors used a defibrillator to shock his heart to restore its rhythm.
He said in the deposition that stress, caffeine and lack of sleep triggered the condition. “I feel like I have a lot of worms in my chest. I can hear it immediately when it goes off,” she said.
He also said in the deposition and interview that he contracted hepatitis C in his youth due to intravenous drug use. He said he had been treated and had no lingering effects from the infection.
Mr. Kennedy has spoken publicly about another serious health condition: spasmodic dysphonia, a neurological disorder that causes his vocal cords to move too close together and explains his hoarse, sometimes strained voice.
He first noticed it when he was 42, he said in the deposition. Mr. Kennedy for years made a significant amount of money giving speeches, but business declined as conditions worsened, he said.
He told an interviewer last year that he had recently undergone a procedure available in Japan to implant titanium between his vocal cords to prevent them from involuntarily shrinking.