PARIS -- Feeling old? You've got company. People in nearly all countries of the world, not just affluent nations like the United States, are living on average decades longer than generations born in the previous century. And the trend is gaining momentum, challenging notions about the natural limits of the human life span -- and how a lifetime should be organized.
To examine the new demography, scientific researchers, physicians, economists and social-policy makers from around the world met here last week at a conference organized by the International Council for Global Health Progress and hosted by the United Nations Educational, Scientific and Cultural Organization.
The changes, dubbed a revolution by many speakers, have been rapid and dramatic. Life expectancy at birth across the globe in 1950 was 47; it now stands at 66. Researchers pointed out that by the year 2050, nearly one-fifth of the world's population is projected to be over the age of 65 -- compared with 1 percent in the year 1900. In a world where large numbers of people will commonly live decades after current retirement ages, economies, family roles and medicine will all have to adapt, the researchers argued.
"We have a relatively short time to prepare," said Robert N. Butler, a gerontologist who is director of the International Longevity Center at Mount Sinai Medical Center in New York. "We need a new, constructive vision of an aging society. There are philosophical and ethical considerations. How do we use this longevity? Medicine, having created this revolution, has a responsibility to help society adapt."
Life expectancy in both hemispheres, among men and women, in rich countries and relatively poor ones, has catapulted to marks unthinkable a century ago. In the industrialized world 25 years in life expectancy have been gained in the 20th century, more than twice the gain in all previous human history.
"This achievement is not a function of biological evolution," said Butler, "but of social and economic progress, better public health and nutrition, and the application of important medical concepts, such as the germ theory of disease."
Moreover, researchers at the conference came to a consensus that the human life span has no fixed endpoint. The fastest-growing segment of the population is adults over the age of 80. And the percentage of people living to over 100 is also rising dramatically.
The current gains are higher for people in developed than developing countries and for women more than for men. But by the year 2025, the developing countries are projected to catch up, and two-thirds of the world's old people will live there, researchers reported. Children born in the developing world in the past decade have a projected life span that is 10 to 12 years longer than their counterparts born 10 years earlier.
Improvements fueling these longevity gains are not just those helping children live to adulthood. Older adults are now living longer than they used to. Unexpectedly, demographers have found that once people reaches the age of 80, mortality rates plateau. It appears that if they don't succumb to common causes of old-age death, such as cancer and heart disease, before 80, they may not face such problems in their 80s. Researchers do not know what accounts for this counterintuitive phenomenon.
"Mortality decelerates at advanced ages, not only for humans but for other species of life ... ," said James Vaupel, director of the Max Planck Institute for Demographic Research in Rostock, Germany. "There is no evidence whatsoever that there's a fixed maximum life span for any species."
Factors that can affect longevity are biological, social, psychological and environmental, participants agreed. But there is little information on why or how we age.
"The field is so new, there is no agreed-upon definition of aging," said Calvin B. Harley, a biomedical researcher with the Geron Corp. in California. "Insights into the fundamental causes of aging and longevity at the molecular genetic level are very recent," Harley said.
One set of theories suggests entropy -- physical wear and tear -- is at work. Other theories suggest changes in genes preventing cell damage and others repairing damage. Some scientists are also advancing a hypothesis of cell aging that involves the role of telomeres, the DNA sequences that cap chromosomes that prevent mistakes in the DNA instructions when cells are reproduced.
The French researcher Etienne-Emile Baulieu is pursuing a theory that aging is related to a breakdown in hormonal regulation of body functions that could be delayed with an application of the deficient hormone.
Betty Friedan, one of the originators of the women's liberation movement in the United States and author of a book on women's aging, told the conference that the longevity revolution "is a female revolution." Women the world over are living far longer than men, and yet little research has been done about this disparity. There was criticism throughout the conference that researchers focus too narrowly on why people die instead of examining why some people survive.
The social implications of an aging population were hotly debated. Social observers and demographers addressed fears about the depletion of resources, changes in the political power balance between young and old and other potential intergenerational conflicts. The speakers focused on adaptation and a reorganization of work life to permit the continued productivity of older people.
James Birren, associate director of the UCLA Center on Aging, spoke of "lag effects" in institutions that are not adapting quickly enough to the changing demography. Churches and synagogues are beginning now, he said, to serve the needs of an older population instead of focusing on Sunday school for the young.
But in business, advertisers and marketers are still targeting younger age groups, unmindful of the changing demographics ahead. In product development, entertainment and home goods, the aging population is not yet being addressed, he said. In families, the structure is becoming more vertical, with fewer children but several generations of members. Yet housing arrangements and the very design of houses only now are starting to change to accommodate more generations and older family members, he said.
Universities use an outdated model of education, "giving a big dose by the age of 22 which (once) was enough for a lifetime," said Birren. "Now we have multiple careers. What are the universities doing to adapt, to bring the gray-hairs back?"
Conference participants dismissed fears that longevity gains will simply create a larger disabled population. Speakers argued that people are living longer because they are healthier. Francoise Forette, president of France's National Foundation for Gerontology, pointed out that among the elderly in France only 5 percent are in institutions. Claude Jasmin, a cancer researcher and founder of the International Council for Global Health Progress, said gains in life expectancy in France have been outstripped by gains in years without disability.
"We are going from a pessimistic view of aging to an optimistic view because we have real data to show the optimism is justified," Jasmin said.
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