Scientists Debate Humain Life Expectancy
By
Paul Kleyman
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"Superlongevity is simply
not possible," stated Leonard Hayflick, a distinguished scientist from the University
of California, San Francisco, whose discovery of the Hayflick Limit in cell
division four decades ago is regarded as one of the most important breakthroughs
of the 20th century in the understanding of aging at the cellular level. He
ripped into "outrageous claims" by some scientists that humans might well live
past age 150 and asserted that even the elimination of all major causes of mortality,
such as cancer and heart disease, would result in only a 15-year gain in life
expectancy.
"Professor Hayflick and
I disagree" that the upper reaches of longevity are capped, said Kaare Christensen,
a professor at the University of Southern Denmark. He declared, "There is no
evidence that human lifespan is approaching a limit." He presented new findings
on "the remarkable improvement in human longevity" over the past 50 years, showing
that death rates for women in their 80s and 90s in industrialized countries
have declined by half, from 16% to 8%, and that the centenarian population has
doubled every decade.
Hayflick
and Christensen participated in a symposium titled "How Long Can Humans Live?"
at the February annual meeting of the American Association for the Advancement
of Science, held in San Francisco. Although panelists differed on important
issues in longevity research--some of which carry public policy implications
for the future of Social Security, Medicare and Medicaid--all concurred with
University of Chicago researcher S. Jay Olshansky, who said that the panelists
were "pretty much in the same ballpark" in their assessments about average life
expectancy, which differs from an individual's potential for extreme longevity.
Olshansky commented that
"the hair goes up on the back of my neck" when he hears some scientists contend
that life expectancy will commonly reach 150, 200 or more years. He added, "There
are no lifestyle changes, surgical procedures, vitamins, antioxidants, hormones
or techniques of genetic engineering available today with the capacity to repeat
the gains in life expectancy that were achieved during the 20th century."
The coauthor of the new
book, The Quest for Immortality: Science at the Frontiers of Aging (New
York City: W.W. Norton), Olshansky said that "another quantum leap in life expectancy
at birth" of 20 to 30 years or more would have to be gained at the oldest ages,
because mortality for people from infancy to age 30 is now extremely low. Past
increases in longevity have derived from external threats to health, such as
infectious diseases that shortened the lives of children. Now, though, major
causes of death "are biological." He elaborated, "They are arising from entropy
within us, for example, degenerative diseases, chronic illnesses, the diseases
of aging." Although Olshansky allowed that impressive gains at the oldest ages
are "theoretically possible," he said that nothing currently on the scientific
horizon would result in the modification of the biological aging process necessary
to expand human aging so dramatically.
Population aging advances
more and more slowly at higher ages, Olshansky said. The striking rise in the
number of centenarians will have little effect on average life expectancy, he
stressed, "because most of those now reaching their 100th birthdays are the
kind of hearty individuals who previously died in their late 90s." This small
change of only a few years "means a large increase in the number of people who
are making it to very old age," he said. He calculated that given current trends,
average life expectancy at birth would rise to age 85 in the United States by
the year 2189. (The more long-lived Japanese would reach 85 in 2033, the French
in 2035.) He underscored that average life expectancy in the U.S. would not
reach 100 years "until well after everyone alive today has already died."
SOCIAL
SECURITY
Olshansky also discussed
the significant differences in his advice to the Social Security Advisory Council
last year from recommendations made by another member of the panel, demographer
Ronald Lee of the University of California, Berkeley. Several panelists at the
San Francisco meeting, Olshansky among them, endorsed the method that Lee and
colleague Lawrence Carter developed in 1992 for forecasting mortality. But Olshansky
took issue with Lee's suggestion that the Social Security Administration's (SSA)
projections for average life expectancy in the year 2070 were too low at about
age 82 for both sexes.
While Olshansky said he
believes that the SSA's actuaries were close, if a bit high in their estimations
of life expectancy, Lee called on them to raise the figures by 3.7 years, to
about age 86. Lee, who said he supports some form of Social Security privatization,
noted that the increase he anticipates would result in a somewhat larger elder
population. To pay for the retirement of older Americans over the next three-quarters
of a century, he calculated that the increase he expects would add 0.55% to
the current shortfall in long-term Social Security funding to the 1.89% financing
gap now eyed by the SSA. He said that after discussing his figures with the
SSA actuaries, who also consulted with Olshansky, they added about one year
to their projections of life expectancy.
Although Lee's estimates
are based on current patterns of increasing longevity, Olshansky argued that
the slowdown of gains in longevity that he described render past increases less
relevant to future projections because the gains must come from increased life
expectancy past age 65. He believes that the life expectancy gains will be far
less than what Lee expects.
Olshansky took no position
on Social Security financing methods, but said, " I don't think the SSA actuaries
have any better idea of what's going to happen 70 or 75 years from now than
anyone else. My primary recommendation to them was to stop making such ridiculously
long forecasts. I think they shouldn't go out past 30 years. Even that's pushing
it." By law the Social Security trustees must present Congress with annual estimates
of the system's financial health 75 years into the future.
HEALTH
EXPECTANCY
Olshansky also said that
the SSA should not rely so heavily on statistical extrapolations of life expectancy
and should pay more attention to the biological realities of aging. He urged
the SSA actuaries to begin considering measures of health expectancy in their
yearly deliberations. He explained that health expectancy is a statistical measure
used to examine levels of frailty and disability in a population. Both Olshansky
and Lee agreed that such measures would have important implications for Medicare,
Medicaid and programs for long-term care.
Olshansky said that health-expectancy
measures, which are gathered by most economically advanced nations, would, for
example, enable the SSA to understand whether declining death rates from heart
disease or some cancers are adding healthy months or years of life--or unhealthy
ones where elders require more assistance. Furthermore, he observed that the
SSA may be unrealistic in showing rising life expectancy in its high, middle
and low estimates. Olshanshky asserted that the worldwide rise in infectious
and parasitic diseases suggests that the SSA should consider the possibility
that life expectancy might decline.
"The other important thing
to realize," he continued, "is that people who have made it out to older ages
in recent decades are a highly selected subgroup of the population. In the future,
these people are not necessarily going to be so robust. You're going to have
much great diversity, much greater heterogeneity, in the kinds of people who
are making it out past the ages of 65, 75 and 85. While there will be a lot
of very healthy individuals over the ages of 70, 80, 90, even 100--there will
also be a rapid increase in the number of frail elderly people. So you'll see
change at both ends of the spectrum."
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