UC
Berkeley demographer finds first evidence that maximum age at
death in humans is rising
28
Sep 2000
By
Patricia McBroom, Media Relations
EMBARGOED
FOR RELEASE UNTIL SEPT. 28, 2000, AT 2 P.M. EST (11 A.M. PST),
TIME OF PUBLICATION IN SCIENCE
Berkeley
- The oldest age at death for humans has been rising for
more than a century and shows no signs of leveling off,
according to a demographer at the University of California,
Berkeley.
This new
finding, based on Swedish national death records for each
year since 1861, calls into question the belief by many scientists
that the human life span has a set end-point of 120 years.
In research
published today in Science, the nation's premier science journal,
UC Berkeley associate professor of demography John Wilmoth
and his colleagues in Sweden and the United States show that,
in the1860s in Sweden, the oldest ages at death for men and
women centered around 101. That average maximum age moved
up slowly throughout the century to about 105 in the 1960s
and then accelerated to 108 in the 1990s.
"We have
shown that the maximum life span is changing. It is not a
biological constant. Whether or not this can go on indefinitely
is difficult to say. There is no hint yet that the upward
trend is slowing down," said Wilmoth.
Wilmoth
said that Swedish demographic statistics - considered the
world's best records on birth and death - are a good indication
of patterns in other industrialized nations, where it has
become commonplace to survive to a very old age.
But until
now, there has been no evidence that the maximum age at death
was being pushed back, leading to a lengthening of the human
life span, said Wilmoth.
"Human
progress is real, somehow," he said. "We are changing the
limits of the human life span over time."
For individuals
alive now, the current life span makes it rare to live past
110 years, said Wilmoth. "But future generations could have
a higher range."
Such statements
run counter to recent predictions by other experts in the
field who theorize that the human life span is biologically
limited to 115 or 120 years.
"Those
numbers are out of thin air," said Wilmoth. "There is no scientific
basis on which to estimate a fixed upper limit. Whether 115
or 120 years, it is a legend created by scientists who are
quoting each other."
Historical
records, on the other hand, show that the entire configuration
of ages at death in Sweden has been shifting upward for 138
years, he said. The upward trend accelerated suddenly around
1970, more than doubling the rate at which the life span was
growing, from less than one year of age for every two decades
to more than one year per decade.
This has
happened because of medical and public health advances throughout
the century, said Wilmoth, whose analysis ruled out simple
population growth as a factor. Some scientists had thought
that the increased number of very old people could be due
to a larger population base, but Wilmoth's data show that
the main cause is increased survival after age 70.
Earlier
in the century, the lengthened life span was probably due
to public health measures such as better sanitation, a safer
water supply and control of infectious diseases.
While it
is well known that these measures increased life expectancy
- the average age at death - especially by lowering child
mortality, Wilmoth believes that better public health also
increased the maximum age at death by creating a healthier
population in old age.
"The elderly
today are benefiting from the fact they were not as sick when
they were children as in past generations, and these changes
took place 80 to 100 years ago," he said.
As for
the spurt upward in 1970, Wilmoth's data shows that survival
after 70 was due overwhelmingly to improved medical practice
concerning heart disease, stroke, smoking cessation, and the
development of new drugs.
"After
1970, the trend began to slope upward rapidly," said Wilmoth.
"That corresponds closely with breakthroughs in certain medical
practices such as understanding and treating heart disease
and stroke."
Wilmoth
also analyzed the age at death for the individual who lived
the longest from each yearly birth cohort between 1756 and
1884 and found a similar upward trend in the life span.
The longest-lived
person born in 1756, for instance died in 1857 at the age
of 101, while the longest-lived person born in 1884 died in
1993 at the age of 109.
As in most
other demographic data, men had a slightly lower maximum life
span than did women, but the gender difference was much smaller
than with life expectancy. Life expectancy is the average
age to which people are expected to live when they are born.
Men in
the United States can expect to live, on average, to age 72
while women live to 79, a difference of about seven years.
But in great old age, the gender difference shrank to less
than two years in Sweden's records on maximum age.
In the
world today, said Wilmoth, "there are currently about two
dozen documented cases of people over 110 years of age - a
handful of men and a few handfuls of women."
###
Links:
UC
Berkeley Department of Demography
Science
Magazine
.
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