His autopsy came back “normal,” and the medical examiner’s “working diagnosis” was that a sudden electrolyte shift caused an abnormal heartbeat, which might have been aggravated by a small, unseen area of heart muscle inflammation, said Lipton’s father, Dr. Jordan D. Lipton, an emergency medicine physician.

“We miss and love him terribly and are devastated that he will never be able to continue the work he loved and the good things he was doing for everyone, while we watched with pride and admiration,” Dr. Lipton told the Globe. “We miss his future, and of course, the lack of a definitive explanation makes it even more devastating.”

Deaths and cardiac arrests involving young athletes are shocking, and often receive media attention. In May, a 27-year-old man from Brooklyn died after running a half marathon in Providence. In July, Bronny James, the 18-year-old son of NBA star LeBron James, was hospitalized and survived after going into cardiac arrest during basketball practice.

But deaths among young athletes are rare, and the benefits of exercise outweigh the risks, said Dr. Paul D. Thompson, chief of cardiology emeritus at Hartford Hospital, and past president of the American College of Sports Medicine.

When he was on the Brown University faculty, Thompson and others wrote a 1982 Journal of the American Medical Association article reporting that just 12 men died while jogging during a six-year period in Rhode Island. They concluded the state had seen only one death per year for every 7,620 joggers.

In 2007, Thompson and others wrote a New England Journal of Medicine article, assessing cardiac arrests in US marathons and half-marathons from 2000 to 2010. They found that of 10.9 million runners, 59 had cardiac arrests, an incidence rate of 0.54 per 100,000. Cardiovascular disease accounted for the majority.

“I don’t want people to get freaked out about the danger of exercise,” he told the Globe.

Thompson — who qualified for the 1972 US Olympic Marathon Trials as a third-year medical student, and finished 16th in the 1976 Boston Marathon — said most people who die while exercising are older men with blocked arteries.

Deaths among young athletes can involve hypertrophic cardiomyopathy (thickening of the heart muscle), abnormalities in coronary arteries, arrhythmogenic right ventricular dysplasia (a rare familial disorder), and inflammation of the heart caused by viral infections, including the coronavirus, cardiologists said.

But Lipton said an examination of his son found no vascular disease, genetic cardiac testing was normal, and he had good cholesterol levels. He said his son had been vaccinated and had COVID-19 a year earlier, but the exam showed no heart inflammation.

Thompson said that when people die of cardiac arrest for unclear reasons, those cases are categorized as Sudden Arrhythmic Death Syndrome, or SADS. “When there is no explanation, we put those together as SADS, and boy, I tell you, it is sad,” he said. “These are usually young people.”

In those cases, the heart goes into ventricular fibrillation, twitching and failing to move blood, he explained. Underlying causes include Long QT syndrome — a heart signaling disorder that can cause fast, chaotic heartbeats — or Brugada syndrome, a rare but potentially life-threatening heart rhythm condition, he said.

“As time goes on, we find more and more deaths during exercise are related to SADS,” Thompson said.

The coronavirus and COVID-19 vaccines can cause heart inflammation in rare cases, Thompson said. “But I am not an anti-vaxxer. The benefits outweigh the risks. I have had four shots.”

Thompson noted some advocates want to screen young athletes for conditions that might cause cardiac arrest. But he said those programs aren’t worth the effort because the problems are so rare. He said that effort would be better spent teaching CPR and making defibrillators available.

Lipton said paramedics used a defibrillator on his son “relatively quickly” after he lost a pulse. Also, two doctors were at a medical tent and helped load his son into the ambulance, he said. One doctor was preparing to intubate him, he said, “but they were reportedly kicked off the ambulance by the medics due to being ‘against their protocol.’ “

While Lipton’s working diagnosis is a “sudden electrolyte shift,” Thompson said, “I wouldn’t blame it on electrolyte abnormality. That sounds like something pushed by sports drinks people.”

Dr. Steven Lome, a cardiologist in Monterey, Calif., said the most common cause of death during marathons among women with structurally normal hearts is hyponatremia, when sodium levels in blood become abnormally low. “If you overconsume water, it dilutes the blood,” he said. “That can induce an arrhythmic ventricular fibrillation.”

Runners can also die from hyperthermia when body temperatures become abnormally high, Lome said. But when Lipton ran the Mesa (Arizona) Marathon, temperatures ranged between 46 and 69 degrees, and a finish line photo shows him looking relaxed, gliding with both feet off the ground.

Lome made national news in 2022 when he performed CPR on two runners during one half marathon in California, helping to save their lives. But he said both runners were much older than Lipton — men in their 50s and 60s, with family histories of heart disease.

Lome said at least 80 percent of heart disease is preventable. As the founder of the Plant Based Nutrition Movement, he encourages plant-based or Mediterranean-style diets, and he emphasized the importance of not smoking, checking your cholesterol, and paying attention to risk factors like a family history of heart problems.

Lipton said there is a family history of high cholesterol, but his son’s exam “was completely normal and his previous lipids were fantastic due to his healthy lifestyle.” He said his son adhered to a “mostly vegan” diet, and was “the healthiest person in our entire extended family.”

Pierre Lipton’s girlfriend, Eleanor Pereboom, said, “I know that Pierre was running fully within his capabilities, and I don’t know anyone who treated their body with more respect than he did.”

Dr. Brian G. Abbott, of Lifespan’s Cardiovascular Institute and Brown University’s Warren Alpert Medical School, said the most common reason for sudden death in young athletes is thickening of the heart muscle leading to arrhythmia. If a person’s heart is structurally normal, other possibilities include the Long QT syndrome that can lead to irregular heartbeats, but most 26-year-olds don’t take tests to screen for such conditions, he said.

“The benefits of running and exercise far outweigh the potential risks,” Abbott said. “Whatever he had was something not clinically apparent. Obviously, he was running fine, he said. “In a way, it’s like getting hit by lightning.”

Lipton said he certainly hopes that whatever happened to his son is extremely rare. “But when it happens to a person like our son, it doesn’t matter,” he said.

Edward Fitzpatrick can be reached at edward.fitzpatrick@globe.com. Follow him @FitzProv.