BBC News By Jonathan Amos in San Francisco
 Life
expectancy for humans is unlikely to reach 100 years or beyond
for quite some time to come, if ever, a US scientist believes.
Jay Olshansky,
Public Health Professor at the University of Illinois, at Chicago,
said on current trends life expectancy rates would not reach 100
until at least the 22nd Century in France and the 26th Century
in the United States.
This pessimistic
outlook comes as research suggests that the lifespan of a mouse
can be greatly increased by anti-oxidant treatment.
The same team
of US researchers, based at the Buck Institute, has already doubled
the lifespan of a worm.
It believes
that one day, the same approach might help humans live longer.
However, Olshansky's
assessment, to be published in the journal Science this week,
is based on an analysis of data on death rates and life expectancy
for men and women of all ages in Japan, France, and the United
States.
Professor
Olshansky said the assessment showed that while many people were
living longer, the rise in life expectancy was slowing down.
The professor
announced the results of the study early at the annual meeting
of the American Association for the Advancement of Science in
San Francisco.
Next leap
The oldest
person ever to live, according to documented records, was Frenchwoman
Jeanne Calment, who died aged 122 in 1997. But Professor Jay Olshansky
said the majority of people were unlikely to live beyond 85 because
their bodies would simply wear out.
"The
human body was not designed for long-term use," he said.
"It was designed for short-term use and in effect what we're
doing is pushing these bodies beyond the end of the warranty period
for living machines.
"So when
we survive into old age, just as with automobiles and race cars,
things start to go wrong, and unless we can change the structure
of the body itself or the rate at which ageing occurs, then inevitably
things will go wrong as we push out the envelope of human survival,"
he said.
Professor
Olshansky was optimistic that people would continue to live longer
but the next quantum leap in life expectancy could only occur,
he said, if "biomedical researchers can discover how to modify
the ageing process and make such a discovery widely available
to the entire population".
Evolving age
Also speaking
to the AAAS meeting, Professor George Martin said that the body
was the major flaw in boosting longevity as the evolutionary system
had no particular interest in helping people live past their peak
productive years.
Professor
Martin, associate director of the Alzheimer Disease Research Centre
at the University School of Medicine in Seattle, said there were
thousands of genes in the human body which could go wrong in different
ways in each person.
He said the
human body could evolve its own systems for increasing life span,
but that this was unlikely to be the same for everyone.
"The
bad news is that there are so many different things that can go
wrong as we age. These can be affected by an enormous number of
potential inborn genetic variations that can modulate how we age,"
he said.
Mark Eshdoo,
director of the Buck Institute, which is carrying out the mouse
research, told BBC News: "I think all humans and all animals
have a certain natural lifespan, but that lifespan can be often
determined by their environment.
"Can
we do the same thing in humans. Yes we absolutely can."
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