Dr. Leila Denmark was a practicing pediatrician in Georgia until she was 103, and lived to be 114. Irving Kahn traded stocks on Wall Street until he died at age 109. His three siblings all lived past 100, too.
Many centenarians don't just live to be 100 — they thrive until the day they die.
Scientists have observed for decades how this longevity seems to run in families, suggesting that people's genes could be driving whether they live to be 100 or not.
But only in the last few years have geneticists began to parse out which genes could actually be responsible for this incredible endurance.
In a recent study, researchers identified five specific gene variants that centenarians shared more often than the general population. They published their results December 17 in the journal PLOS Genetics.
Even more exciting than the five genes they found is how they found them: using a new strategy that might kick this kind of research into high gear and help scientists more quickly piece together the puzzle of why a lucky few stay healthy past 100.
'A genetic street address'
It can take a long time to scan the entire human genome. So Stuart Kim, senior author of the study from Stanford University, told Tech Insider that the researchers decided to try a new technique, a shortcut of sorts to help them zero in on the relevant pieces. They focused on genes that we already know are associated with certain diseases, and looked at whether or not those genes also have a connection with longevity.
A locus (plural: loci) is where a DNA sequence is, physically, in your genetic code. You can think about it as "a genetic street address," as the National Library of Medicine suggests. Due to variation and mutations in the human genome, some people will inevitably have different versions of a locus — not everyone has the same thing in a given genomic location — and one may be associated with increased risk for a certain disease, while another version won’t.
Kim and his team found five particular loci were present in people who lived to be 100 that weren't as common in the general population. These loci have been linked to Alzheimer's, cellular problems that can lead to cancer, autoimmune diseases, and neurological issues. Centenarians were also more likely to have the O blood group.
In the general population, the loci that have been shown to play a part in causing these diseases were common. But centenarians were much more likely to carry a different loci in their genes that seemed to have a protective effect, making them less likely to get these diseases.
In a statement, David Cutler, a geneticist from Emory University who wasn't involved in the research, cautioned that these findings are merely associations — having the kind of loci they identified is not an ironclad predictor of reaching old age.
The authors show that "if allele A is associated with a slightly increased risk of fatal disease and therefore dying younger, the opposite of allele A is associated with a slight propensity to live longer," Cutler said. "This is perhaps not surprising ... There are a million ways to die, and alleles that are associated with any fatal disorder are probably weakly associated with not living to great age."
And genes are only part of the equation. "How well you age is in your hands in terms of living to almost 90," Thomas Perls, an attending geriatrician at Boston Medical Center and professor at the Boston University School of Medicine, previously told Tech Insider. Exercise, a healthy diet, low stress, and a smoke-free life will get most people that far.
But joining the centenarian club is a different story.
Only 17.3 per 100,000 Americans live to be 100, so figuring out what is special about their genes — and it's likely a lot of different things — could one day help to develop drugs or treatments that ward off old age, or at least some of the diseases associated it.
"In 1900, the median lifespan was 46. In ancient Greece and Rome, the median lifespan was about 26. So human lifespan has really increased over historical time," Kim said. Yet "right now, as much as you try — let's say you’re a billionaire — it's not easy to live an extra 20 years."
And while the current assumption is that, as Perls noted, "about 110 is really approaching the limit of the human lifespan," that could change.
As Kim suggested, "Maybe lifespan is really plastic."
