Medical Physiology, 3rd Edition

CHAPTER 62. The Physiology of Aging

Edward J. Masoro

Biomedical science paid surprisingly little attention to a remarkable change in human biology during the 20th century—the marked increase of human life expectancyimageN62-1 in developed nations. Life expectancy is the projected mean length of life of those born in a given calendar year (e.g., 1984)—or those of a particular age (e.g., 30 years)—computed from the mortality characteristics of the entire population in a particular year (e.g., 2016). In the United States, life expectancy for men progressively increased from 47.9 years in 1900 to 76.4 years in 2012, and for women, from 50.7 years in 1900 to 81.2 years in 2012. imageN62-2

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Life Expectancy

Contributed by Emile Boulpaep, Walter Boron

Human life-expectancy data—such as those cited in the first paragraphs of this chapter—are computed from mortality data for a particular year (e.g., 2002)—that is, the ages of all people who happen to have died in a particular year. Note that some of these individuals who died in 2002 were born in 2002, and some were born in 1900. The first step in computing life expectancy is to use the mortality data of 2002, for example, to compute age-specific death rates, from which we can derive a variety of other statistics. For example, we can compute the life expectancy at a particular age. The life expectancy at birth in the United States in 2002 was 74.5 years for men and 79.9 years for women. However, based on 2012 data, the life expectancy at birth in the United States had already risen to 76.4 for men and 81.2 for women. Clearly, these life expectancies are not predictions about how long someone alive today will live. Rather, they are death rates that are frozen in time.

Another way of approaching the question is to analyze an extinct cohort, such as all those born in the year 1800. Based on the age at death of each member of this cohort, we could compute the true life expectancy of those born in the year 1800. Note that it is impossible—today—to predict the true life expectancy of those born in the year 2000 because that cohort is not extinct.

References

Arias E. United States life tables, 2004. Natl Vital Stat Rep. 2007;56(9):1–40 http://www.cdc.gov/nchs/data/nvsr/nvsr56/nvsr56_09.pdf [Accessed July 16, 2015].

Heron MP, Hoyert DL, Murphy SL, et al. Deaths: Final data for 2006. Natl Vital Stat Rep. 2009;57(14):1–135 http://www.cdc.gov/nchs/data/nvsr/nvsr57/nvsr57_14.pdf [Accessed July 16, 2015].

Wikipedia. s.v. Life expectancy. [Last modified July 15]  http://en.wikipedia.org/wiki/Life_expectancy; 2015 [Accessed July 16, 2015].

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National Institute on Aging

Contributed by Edward Masoro

Responding to the increase in life expectancy, the United States in 1974 established the National Institute on Aging (NIA) in the National Institutes of Health. The NIA has had a major impact in the United States and throughout the world in the promotion of research on aging and in the development of geriatric medicine.

Concepts in Aging

Cellular and Molecular Mechanisms of Aging

Aging of the Human Physiological Systems

Aging Slowly

References