Life expectancy data from the past 50 years
shows that people who survive to age 65 are continuing to live longer than
their parents – a trend that doesn’t appear to be slowing down.
BY SOFIE BATES NOVEMBER
6, 2018
Stanford biologist Shripad Tuljapurkar had
assumed humans were approaching the limit to their longevity – that’s what
previous research had suggested – but what he observed in 50 years of lifespan
data was more optimistic than he was.
Analyzing the average age of death in people who
lived to be over age 65 in developed countries showed that human lifespans are
increasing by approximately three years every generation and that this trend is
likely to continue, at least for a while. The researchers published the results in
the Proceedings
of the National Academy of Sciences.
“The data shows that we can expect longer lives
and there’s no sign of a slowdown in this trend,” said Tuljapurkar, professor
of biology and Morrison Professor of Population Studies. “There’s not a limit
to life that we can see, so what we can say for sure is that it’s not close
enough that we can see the effect.”
Living longer than our
parents
Tuljapurkar and his colleagues wanted to answer
two pressing questions: Is humanity approaching a limit to human lifespans? Are
there factors that allow some people to live longer than others?
The researchers looked at birth and death data
for people above age 65 from 1960-2010. They found that the average age of
death in those who live to be older than 65 increased by three years in every
25-year period, which means that people can expect to live about six years
longer than their grandparents, on average.
Furthermore, this trend continued at a
relatively stable pace over the entire 50-year period and in all 20 countries
that they analyzed. Factors like medical breakthroughs caused minor
fluctuations in how quickly lifespans increased, but these variations averaged
out over time.
The increase in lifespan during any given decade
was very similar.
Getting rid of the
fuzziness
Most longevity studies look at the outliers, the
people who live longer than everyone else. The data get fuzzy, however, because
so few people live that long. Instead, Tuljapurkar and his colleagues,
including Sha Jiang, a visiting graduate student from China, looked only at
people over age 65, an age range with a large number of individuals.
“Our method is novel because it allows us to get
rid of the fuzziness,” Tuljapurkar said. “Our focus is on the age range where
we have an accurate idea of what’s going on.”
If we were about to hit a limit to human
lifespans, the distribution of ages when people die should compress – like a
rolling wave crashing into a wall – as they approach the limit. But the
researchers didn’t see that pattern in the data. The wave continued to move
forward.
Definitely not yogurt
Tuljapurkar was surprised to see that the
average age of death increased at a constant speed, but he was even more
surprised that the shape of the distribution didn’t change. He expected that
certain endowments would allow some people to live longer than others.
“There used to be so many ads about how people
could live longer by, say, eating yogurt,” Tuljapurkar said. He wasn’t
convinced that yogurt was the key to a longer life, but he did suspect that
factors like wealth could increase the likelihood that someone would live
longer.
If this were true, the distribution of the data
should widen as rich people live past the average age of death. But the shape
of the data was consistent over the 50-year period they studied. There was no
single factor that allowed some people to live longer than others – at least
not one that was showing up after age 65. Tuljapurkar noted that by the time
someone has reached 65, he has already overcome many of the factors that could
shorten life, like violence or early disease.
“But as someone who would like to be a one-percenter but is not,
I’m certainly very happy to know that my odds of getting to live longer are
just as good as the millionaire down the street,” said Tuljapurkar.
Media Contacts
Amy Adams, Stanford News Service: (650) 497-5908, amyadams@stanford.edu
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