Forever young: No detectable limit to human lifespan
Last October, researchers proclaimed the biological limit to the human lifespan is peaking at 115. But two Canadian biologists from McGuill University argue that analysis was flawed.
Jeanne Calment liked cream cakes, a nightly glass of port and, when she was 110, acquired a taste for those strong, dark and lethally chic French cigarettes, Gauloises.
Calment, the oldest documented person who ever lived, died in 1997 at age 122.
So last October, when Albert Einstein College of Medicine researchers concluded Calment was a statistical outlier, and that the biological limit to the human lifespan is peaking at around 115, the proclamation, published in the journal Nature, made headlines worldwide. “From now on, this is it. Humans will never get older than 115,” Jan Vijg, an Einstein expert on aging, told The New York Times.
Now, however, two Canadian biologists, in a critical comment published in Nature, argue the Einstein supercententarian analysis was flawed and that there’s no evidence the maximum human lifespan has reached a plateau.
“We just don’t know what the age limit might be,” McGill experimental biologist Siegfried Hekimi said in a statement. “In fact, by extending trend lines, we can show that maximum and average lifespans could continue to increase far into the foreseeable future.”
Hekimi, a 60-year-old professor of biology and former professional cyclist (his most memorable race the Tour de France in 1982), works with worms and mice. His lab has shown that by making a single change in the smallest piece of DNA of nematode worms, the animals can live five times longer, work that could one day open the door to interventions to slow our own biological rate of aging.
Hekimi believes it’s not out of the realm of possibility humans could live to 150, or beyond. Longer life, he adds, doesn’t necessarily mean extra years of poor health. Observational studies of centenarians show that people aren’t “hanging in, staying alive, despite disease,” he said in an interview. “They just didn’t get sick.
“Whether it was luck or their genotype, that can be a debate. But the fact is that, mostly the people who live a very long time, they were always healthy. They didn’t have heart disease or diabetes.” Almost unavoidably, he said, an increased life span means a longer, healthy lifespan. (Though virtually blind and hard of hearing, and apart from mild heart failure and rheumatism, Jeanne Calment had reportedly been in good health a month before she died.)
When the Einstein study was published in October, putting the biological limit to human life at 115 years, “it was obvious to me this was a weak analysis,” Hekimi said.
The Einstein group analyzed data from people verified as living to age 110 or older between 1968 and 2006 in the four countries — the U.S., France, Japan and the U.K — with the largest number of the longest-lived.
The age of death of the supercentenarians increased rapidly between the 1970s and early 1990s, but reached a plateau, they reported, around 1995.
They concluded that people who reach their 110th birthday today have no greater life expectancy than those who lived to 110 in the 1970s, and that the age of death of the world’s oldest person hasn’t increased since Calment died in 1997.
“Further progress against infectious and chronic disease may continue boosting average life expectancy,” Vijg said when the study was released, “but not maximum lifespan.”
But when they analyzed the same data, Hekimi and co-author Bryan Hughes questioned why the Einstein team split their data into two groups: one before a certain arbitrary date and one after.
Without dividing the dataset in two, the McGill duo found a long-term increasing trend in maximum life, with no current evidence of plateauing. Theirs is one of five critiques of the original paper.
Since Confederation in 1867, Canadians’ life expectancy has more than doubled to 82 (80 for men, 84 for women).
Hekimi says it stands to reason maximum life span will follow the same trend, meaning there’s no indication that while average life span goes up maximum lifespan won’t go up in parallel.
“If this trend continues and our life expectancy of the average person becomes 100, the longest person might make it to 150,” he said. “Probably not you or me. But maybe our grandchildren and great-grandchildren, because it’s an ongoing process.”
The Einstein team, in a response, said they remain confident in their results.
While there may be no detectable limit yet to how long people can live, it doesn’t mean there’s a limitless lifespan. The 2016 Canadian census counted 8,230 centenarians, a 41 per cent increase over 2011 figures. “So, people are moving into age 100, but we have no idea where that will end,” said Parminder Raina, scientific director of the McMaster Institute for Research on Aging. “Will these people continue to live longer and longer, or is there a certain limit to life expectancy? I think it’s an open scientific debate.”
The oldest Canadian supercentenarian alive today is Ellen “Dolly” Gibb, of North Bay, who celebrated her 112th birthday in April.
Original article at: http://nationalpost.com/news/canada/no-detectable-limit-to-human-lifespan
Photo credit: AP (Feb. 12, 1996 file photo shows Jeanne Calment in Arles, France. Believed to be the world’s oldest person, she died at the age of 122 in 1997.)