By Dean A. Haycock
Special to BioWorld Today
It's "common knowledge" that life expectancy in developed countries will continue to rise in an impressive and welcome manner. After all, the life expectancy at birth for a female born in the United States increased nearly 30 years during the last century. So, many people reason, with access to good medical care and a healthy lifestyle, future generations might expect to live to 100.
But it's not likely, according to S. Jay Olshansky and his colleagues. In a paper in the February 23, 2001, issue of Science, "Prospects for Human Longevity," the authors estimate that life expectancy in the U.S. won't reach 100 years until the 26th century.
Their estimate assumes that age- and sex-specific trends in death rates observed from 1985 to 1995 continue. If so, they contend, "life expectancy at birth for males and females combined would reach 85 years in 2033 in France, 2035 in Japan, and 2182 in the United States." French and Japanese could expect to live 100 years sometime in the 22nd century.
Demographer-economist Ronald Lee of the University of California at Berkeley doesn't agree with all of the estimates in the Science paper. Lee finds it striking that Olshansky and his co-authors predict that life expectancy in the U.S. won't reach 85 years until 2182.
"I find this really astonishing," he said. "I don't have the details of the calculation before me, but I do know he is looking at rates of decline from 1985 to 1995. First of all, that is far too short a period to be basing long-run projections and extrapolations on. Secondly, it is completely arbitrary to stop that calculation at the year 1995 since we have final National Center for Health Statistics data for 1998 in the U.S. The gain in life expectancy just between 1995 and 1998 is a full year, which is almost the same as the gain between 1985 and 1995. If he had included those last three years, he would have gotten a much more rapid rate of decline [in mortality]."
Ten years ago Olshansky and his colleagues published a paper in Science in which they said it was unlikely that life expectancy for males and females combined was going to exceed 85 years unless new research comes up with some widely available, age-extending process.
Declines In Death Rates Not Enough
"There were a number of people who said that the progress we can make in the biomedical sciences, starting [in 1990], will permit us to achieve much more rapid declines in death rates than have been observed in the past, and much more rapid increases in life expectancy than we anticipated," Olshansky told BioWorld Today.
He and his co-workers saw that as a testable hypothesis, so they waited. At the end of their decade-long wait, they found that while death rates were declining in Japan, France and the U.S., the decline was not enough to raise life expectancy at birth to the higher levels suggested by some other researchers.
"The more optimistic researchers . . . predicted a 2 percent decline in death rates at every age from 1985 forward," Olshansky recalled. "In fact, in the U.S. the average rate of decline from 1985 to 1995 was about 0.4 percent, about one-fifth the rate of decline they had anticipated. We demonstrated in 1990 that the measure of life expectancy is an insensitive one. We predicted the rise in life expectancy would decelerate - and it has."
Many individuals will live past 75, 85 and 95 years but, according to the author, life expectancy won't increase very much. This is because death rates and life expectancy data for men and women of all ages from 1985 to 1995 indicate that the rise in life expectancy observed over the last century is slowing down.
"The future is not going to be like the past because we are operating in a different world today," Olshanksy explained. "The majority of declines in death rates observed in the 20th century occurred at younger ages. That can only be achieved once in a population. This means that the only way to get a get another quantum leap in life expectancy is to add decades of life to people at older ages. That is a far more difficult thing to achieve because you are now coming up against the aging process itself."
Although the U.S. has not experienced it as much as other developed nations, Lee said that "generally there has been an acceleration in the rate of decline of mortality at ages over 70 over the last few decades. I just don't see any evidence for the kinds of changes that Olshansky is predicting will occur."
Drugs Acting On Aging Are Best Bet
It is routine to project life expectancies by extrapolating from changes in death rates observed in the past into the future. "A lot of careful thought goes into the projections but you have to realize that they are projecting death rates that are a product of a biological phenomenon," Olshansky said. He uses the world's record for running one mile as an example. A linear extrapolation of that trend would suggest that someone could someday run a mile in one minute, and eventually, someone would cover a mile instantaneously.
"Of course, that is a ridiculous notion," Olshansky said, "because there are biomechanical constraints that influence how fast humans are capable of running. And yet we are using a mathematical model that completely ignores the underlying biology in humans to make predictions. It is the exact same story when it comes to human life expectancy and longevity. Over the long run, you cannot use purely mathematical models to make projections about life expectancy because [they] are biological phenomena that have constraints influenced by the underlying biology of the organism."
Significant advances in life expectancy will have to come from the development of pharmaceuticals that are designed to alter the aging process itself, Olshansky said. "In other words, the only way to get these large increases is to alter aging, not to combat the disease associated with growing older."
For Olshansky, the biotech and pharmaceutical industries are the only industries that have the potential to produce another quantum leap in life expectancy. But the goal, he suggested, should not be so much to add years to life, but to make the years we have healthier. n