Maximum Life Span
(10/10/00)- Has there been an increase in the maximum life span of humans in the last centuries? Wilmoth et al, in a study of the maximum age at death in Sweden suggests a resounding "yes" to this question. Quoting from their study: "National demographic statistics support that the maximum age at death has been rising in industrialized countries for more than 100 years." This upward movement of maximum human life span is reflected in the death of Jeanne Calmet at the documented age of 122.45 years.
Wilmoth et al (1) performed a careful statistical analysis of the longest available series of reliable information on the upper limits of achieved human life span. This group of researchers found that from 1969 to 1999 maximum life span increased by 1.1 years every decade. There was also a difference between the maximum life span of men and women, with the maximum age at death for men about 1.7 years lower than women during the same period noted above.
This study stands to refute the common assertion that human life span is fixed and unchanged over time. Wilmoth et al conclude: "Reduction in death rates at older ages, which have accelerated in recent decades, seems likely to continue and may gradually extend the limits of achieved human longevity ever further."
Studies (5) also indicate that the average number of years that people spend disabled has grown faster than those that they spend healthy. People are spending their young and middle years enjoying health, but this improvement is at a price, reflected in spending more time disabled when they are older, an increase in dependent life.
The two main difficulties an older population face are decline in motor function and decrement in memory. This involves lowered capacity to handle tasks requiring coordinated control of motor and reflexive responses and tasks that require the ability to acquire a cognitive representation of location in space and the ability to effectively navigate the environment. These are major factors that affect the length of reliance on others i.e. dependent life. The object now is to increase the years of functioning capacity i.e., decrease the transition to poor capacity. Olshansky, Carnes and Cassel (2) suggest "Conceivably… medical researchers may learn how to slow the rate of senescence itself, thereby postponing the onset of degenerative diseases and the cause of old-age mortality. Toward that goal, many scientists working in the fields of evolutionary and molecular biology are now trying to learn why organisms become senescent." A recent edition of Science (2000; 289:1754-1757) (3) describes how certain cells can be steered into new career paths, something that no one had considered possible. While this coaxing of cells was done in vitro, and has yet to be done in vivo, it may represent a new approach to treating diseases associated with aging. What Kondo and Raff did make oligodendrocyte precursor cells "back up" through the developmental; cascade. They conclude "The use of extracellular signal molecules to reprogram specified precursor cells in culture to become multipotential stem cells may prove useful for cell therapy, as specified precursors are generally more abundant and easier to purify than multipotential stem cells."
The New York Times (Tuesday, November 7, 2000) (4) quoted Dr. Fred Gage, a neuroscientist at the Salk Institute in La Jolla, Calif. "People are doing fantastic experiments that no one believed are possible. And then others go out and repeat the experiment." Much of this work involves stem-cell research; a controversial issue due to the source of stem cells. All the body tissues and organs arise from embryonic stem cells. The embryonic stem cells disappear once the body is formed, leaving a few descendents to keep the body in good repair throughout its lifetime. However, these adult stem cells lack the capacity to generate any and all of the body’s tissues. They do carry out minor repair work throughout one’s lifetime, but are overwhelmed when serious disease or trauma occurs. Finding ways to rejuvenate and activate these adult cells holds promise in revolutionizing many areas of medicine and helping increase the maximum life span of human beings. The buzzword for this approach is "regeneration medicine". It would not depend on scalpels and medications to repair the body tissue, but would use the same cells and chemical signals used by the body.
Basic research may be developing new avenues to healthier longer lives, lowering years of disability in an aging population, testing the limits of maximum life span in the process. Time will tell.
Reference:
1. Wilmoth JR, Deegan LJ, Lundstrom H, Horiuchi S. Increase of Maximum Life-Span in Sweden: 1861-1991. Science 2000; 289: 2366-2368.
2. Olshansky SJ., Carnes BA. And Cassel CK. The Aging of the Human Species. Scientific American 1993; 268:46-52.
3. Kondo T. and Raff M. Oligodendrocyte Precuror Cells Reprogrammed to Become Multipotential CNS Stem Cells. Science 2000; 289: 1754-1757.
4. Blakeslee S. In Early Experiments, Cells Repair Damaged Brains. New York Times 2000; Tuesday, November 7; Sec. F :F1-continued p.8.
5. Crimmins EM., Hayward MD., Saito Y. Changing Mortality and Morbidity Rates and the Health Status and Life Expectancy of the Older Population. Demography 1994; 31(3): 159-175.
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Harold Rubin, MS, ABD, CRC, Guest Lecturer
November 10, 2000
http://www.therubins.com
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