These days the long-term measure of good health is life expectancy. Data on the life expectancy of men and women, white and black, are shown in the graphic for a 50-year period. For the nation as a whole, life expectancy has increased from just over 67 years at birth to nearly 77 years between 1948 and 2000. In a word, the combination of our regimens of nutrition, exercise, and health care have added ten years to our life span on average.
Black women have made the greatest gains. Their life expectancy has increased 20% in this period, from 62.5 years in 1948 to 75 in 2000. White women (from 71 to 80) show the smallest gains, but white women have the highest longevity rates of any of the subgroups shown. (Notice, incidentally, that in 1948 the Social Security System was doing just fine. Men retired at 65 and then obligingly died six months later.)
Black men had the second best improvement in life expectancy, up 17.6% in this period, from a low 58.1 years in 1948 to 68.3 in 2000. Indeed, the gap between whites and blacks has narrowed in this period. At the beginning, all whites could expect to live 8 years longer than blacks. By the end of the period, the difference had narrowed to 5.6 years.
If "current trends continue," as they say, can we expect to live forever? Don't bet on it. As space travel seems to be limited by the speed of light, so human cellular reproduction seems bounded by the Hayflick Limit. Exceeding the first may be as difficult as breaking through the other. In 1961, Dr. Leonard Hayflick at Stanford found that human cells have a limited life. Different kinds of cells have a different lifespan, but the number of divisions is around 60. We die, ultimately, because, in old age, dying cells far outnumber newly formed cells, and our organs lose functionality. Many theories exist on why and how this happens. Immortalists are hard at work, but don't hold your breath.
More specifically, we're creatures built of cells. Cells are grouped into tissues, tissues into organs. Other tissues connect organs and provide structure to our bodies. Cells divide. Cells age with each division. Over time, cells accumulate pigments and fatty substances inside their walls. They deform — growing larger. Or they deform — growing smaller. They take on abnormal shapes and sizes, called dysplasia. When cells atrophy other cells enlarge or multiply in compensation. Over time, disorder increases in the tissues and in the organs of which the tissues are the components. Organs gradually lose first their "reserve" capacity — their ability to function at high rates in emergencies — and then some of their basic functionality. Connective tissues grow stiff. All this appears to be the consequence of normal cell reproduction and the stresses and strains our cells suffer living in the "big city," our bodies.
There are early indications, particularly in the life expectancy data for white women, that growth in life expectancy may be slowing, flattening out. This may be a temporary phenomenon or may mean that we are nudging up against the Hayflick Limit. Once we reach it, progress is bound to be slow. At present there isn't even a consensus on the number of cells we have in our bodies. Estimates range from 7.5 trillion on up to 100 trillion, although the lower number appears to be closer to the truth and is the result young people get when doing estimates in Biology Class, using body mass and cell volume. In any case, there are many, many cells we must fix, train, or reinvent before we routinely dress for our morning jog at age 155.
Source: National Center for Health Statistics. National Vital Statistics Report, v. 47, no. 28. 13 December 13 1999. Population data from the U.S. Bureau of the Census.
1 Age-adjusted death rates are indexes so that the rates can be compared from one year to the next. The so- called "crude" death rate is influenced by changes in the age structure and does not lend itself well to comparison of data over longer periods.
2 Reported in Centers for Disease Control's Morbidity and Mortality Weekly Report, 1998; 47:945-949.
3 These data are taken from actual measurements. When asked to judge themselves, more men report that they are obese than women, as shown by the CDC's Behavioral Risk Factor Surveillance System (BRFSS). Men are too honest, women too modest. For details, see http://www.cdc.gov/nccdphp/dnpa/obesity/trend/prev_char.htm.
4 The author of these lines was able to write them because of an intervention not yet attempted when he gave away his first daughter in marriage.
5 Perls, Thomas T. and Ruth C. Fretts, "Why Women Live Longer than Men," Scientific American, June 1998, accessible at http://www/sciam.com/1998/0698womens/0698persl.html.
6 Please use with caution. Preliminary 2000 totals are used, distributed using 1976-1999 averages for occur- rence. Data are intended to be illustrative only.
7 United Nations, ACC/SCN (2000) Low Birthweight: Report of a Meeting in Dhaka, Bangladesh, 14-17 June 1999. Eds. Pojda J and Kelley L.
8 "Current Tends in Infant Mortality-United States, 1988," Morbidity and Mortality Weekly Report, September 21, 1991, Centers for Disease Control and Prevention.
9 "Sudden infant death syndrome," MEDLINEplus, accessible at http://www.nlm.nih.gov/medlineplus/ency/article/001566.htm
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