Still, Barzilai said more developments are on the way.
"This is what we're excited about -- there is a way to find a gene and then strategize and develop a therapy," he said.
Many in the Wellderly study have a range of reasons they think they've been so healthy, said Sarah Topol, a registered nurse and clinical trials coordinator for the Scripps Translational Science Institute. Topol, the daughter of the study's director, has interviewed all of the more than 1,300 participants over the phone and met many in person to take their blood or saliva samples. Participants must be in their 80s, with the average age about 87.
She said they have a wide range of personal habits from those who smoke and drink, to those who abstain and run marathons. The one link she sees is a positive attitude.
Optimistic Personalities
"There's nothing in their lifestyle that could explain it," she said. "I think that the most common theme is that people are upbeat, have a good sense of humor and just see the positive in life."
Most resist visiting doctors and taking their advice, Sarah Topol said. Many take supplements and will change their diets instead of taking prescription medicines, such as a 103-year-old woman in Riverside, California, who swears by a mushroom compound and an extract from lion's mane.
"She was feisty. I sat down with her and she said, 'I think I can fight you. I can fight anybody,'" Topol said. "She wanted to teach me how to shoot a bow and arrow."
Markam, the 83-year-old San Diego resident, also takes supplements containing fish oil, red yeast and glucosamine. He doesn't think his genes are anything special but feels lucky to have survived World War II and, later, being run over by a truck. He spends most of his time now running errands and tending a small garden of roses and a lemon tree in his backyard, as well as cracking jokes about his long and healthy life.
"They're trying to figure out how I could live so long and be so ugly," he said.