Just how long can humans live?
Biologists at Montreal's McGill University have been studying the question and say if there's a limit, they haven't found it.
"We just don't know what the age limit might be," said Siegfried Hekimi. "In fact, by extending trend lines, we can show that maximum and average lifespans could continue to increase far into the foreseeable future."
'Maximum and average lifespans could continue to increase far into the foreseeable future.' - Siegfried Hekimi, McGill University
A previous study looked at the lifespan of the longest-living individuals from the U.S., the U.K., France and Japan for each year since 1968 and concluded that the maximum human lifespan is approximately 115 years.
But Hekimi and colleague Bryan G. Hughes took issue with the methods used in that study and reanalyzed the data.
"We show that there is no plateau," Hekimi told CBC News.
The findings were published Wednesday in the journal Nature.
Hekimi said no one has demonstrated that the human body has an expiry date, or that internal mechanisms can be exhausted.
"Such biological processes exist, but it doesn't mean these biological processes function like a clock that goes ding ding ding," he said. "There is nothing to say they run out at 115."
Centenarians fastest-growing age group
Average lifespans have been creeping upward. In 1920, the average Canadian could expect to live 60 years; a Canadian born in 1980 could expect to live to about 76; today, life expectancy averages 82 years.
Maximum lifespan follows the same trend, Hekimi said, based on experiments with organisms whose life cycles can be manipulated, like mice or certain nematodes.
"When you increase average lifespan, that is almost invariably accompanied by an increase in maximum lifespan," he said.
So when more and more people live to the age of 90, there will be an increase in the number of people who live past 100, and beyond, he said.
The most recent data from Statistics Canada backs that up.
Centenarians are the fastest growing age group in the country, according to the 2016 census, which found 8,230 people 100 or older — a 41 per cent increase over the 5,825 counted in the 2011 census. By 2051, the number of centenarians could reach nearly 40,000, the agency projects.
Living conditions keep improving
Advances in health care don't account for the steady increase, Hekimi said.
"The effects we see on human lifespan in the last 300 years are quite easy to relate to the environment we have built for ourselves: it's warm inside in the winter, it's cool inside in the summer; we eat fresh, uncontaminated food all year long," he said.
Given the better living conditions, it's reasonable to believe people will keep living longer and longer.
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"People who are dying now at 117, their early life was not as easy as that. Wait until we have our entire life as easy as it is now," Hekimi said.
Even in the developing world there have been "very large gains" in lifespan as living conditions have improved, albeit more slowly than in the developed world.
Hekimi and Hughes looked only at demographic data. They did not make predictions of population growth, nor consider the social implications of people living longer.
What is clear, though, is that we are using "huge" resources to create a favourable environment for ourselves, and that's not going to be sustainable.
"There are enough resources on the planet to make everybody as healthy as we are in Canada," Hekimi said, "but it's how you choose to use the resources."