LONGEVITY: SOCIAL ASPECTS

The population of the United States enjoys one of the highest life expectancies in the world, and throughout the twentieth century the life expectancy of Americans increased remarkably. When the twentieth century began, U.S. newborns could expect to live an average of 47 years (see Figure 1). By 1960, that number had risen to 70 years, and it had increased to 76.7 years by the year 1998 (Anderson; Murphy).

Earlier in the twentieth century, life expectancies were volatile. For example, between 1917 and 1918, life expectancy plummeted 24 percent, from 48.4 to 36.6 years, due to the influenza epidemic. Since the introduction of infectious disease–fighting antibiotics in the 1930s, life expectancies have become more stable as they increased. Improvements in health care, social programs, and living conditions have further contributed to increasing life expectancies.

Over time, both males and females have enjoyed substantial improvements. Females have experienced life expectancy gains from 48.3 years in 1900 to 79.5 years in 1998; males life expectancy increased from 46.3 years to 73.8 years during this same period. The life expectancy sex gap gradually widened from 2 years in 1900 to 7.8 years in 1975. It has been closing gradually since, narrowing to 5.7 years in 1998.

Life expectancy in the United States also differs for persons with different social characteristics. For example, racial and ethnic groups vary such that African-Americans have the lowest life expectancy in the United States, Hispanics and non-Hispanic whites have higher life expectancies, and Asian Americans have the highest (Rogers et al., 2000). Persons in higher status educational, income, and occupational groupings also have substantial life expectancy advantages over those in lower socioeconomic statuses.

Survival curves

Mortality trends by age may be visually represented through survival curves, which follow a hypothetical birth cohort of one hundred to show what proportion survives to later ages. Figure 2 compares survival curves for selected years. Note that in the bottom curve, survival probabilities are relatively low, particularly at young ages. In 1900, 20 percent of individuals died between birth and age ten; today, less than 1 percent face a similar fate (also see Table 1). Thus, one distinguishing feature between survival rates of 1900 and today is substantial improvement among infants and children.

In 1900, survival chances were also lower across the entire life span. Out of one hundred newborns, only seventy-seven were expected to reach age twenty, fewer than half were expected to attain age sixty, and just thirty-two were expected to reach age seventy. In contrast, based on 1998 survival rates, almost 90 percent of newborns can expect to reach age sixty.

Between 1900 and 1930, survival drastically improved for infants and children, and also improved for other ages. Between 1930 and 1960, survival improved substantially for middle-aged individuals. And between 1960 and 1998, mortality improvements were significant at the older ages. In fact, individuals aged eighty-five and older have experienced remarkable declines in mortality over the last several decades. Out of one hundred individuals born, just three could expect to live to age ninety in 1930; by 1960, this number doubled, to six; and between 1960 and 1998, this percentage more than tripled.

Rectangularization of mortality

Note the changing shape of the survival curves with time (Figure 2). From 1900 to the present, the survival curve has become more rectangular due to increased survival at all ages, but especially at the young and middle ages. To describe the changing shape of the survival curve over time, Fries coined the concept "rectangularization of mortality."

Debate centers around future reductions in mortality and whether there is a limit to the human life span. Fries argued that while continued improvements will occur at the younger ages, we have witnessed most of the possible mortality improvements at the oldest ages. But based on current survival curves, there is still ample room for improvement in the fifties, sixties, and seventies.

Fries also suggested that greater proportions of individuals will survive to age eighty-five, with few individuals surviving beyond this age. Similarly, Olshansky and others asserted that life expectancies will continue to increase, but at a slow pace, noting that even though mortality has declined for older age groups, neither the right tail of the age distribution nor the age of the verified longest-lived individual has substantially increased. Newer evidence, however, suggests that the survival tail will continue to lengthen. Indeed, there have been noticeable changes in the percentage of individuals in the United States and other countries surviving to the ages of ninety-five, one hundred, and beyond. Some researchers also raise the possibility of much higher future life expectancies, with more and more individuals living to one hundred and beyond (see National Research Council).

It seems reasonable to consider that the life span is not fixed, and can be extended through incremental advances. For example, if life span is currently 122 years and 165 days based on the documented length of life of a French woman named Jeanne Calment (National Research Council), then it seems reasonable for other individuals to live the same length of time plus one day, and so on. In fact, at the oldest ages, mortality has declined and the distribution of ages of death has lengthened for more than a century. From 1870 through 1990 in Sweden, a country with excellent documentation of births and deaths, the oldest reported age has increased about one year for every twenty years of time (Wilmoth and Lundstrom 1996).

Mortality by cause

Life expectancy changes are affected by trends in specific causes of death. Through the early part of the twentieth century, mortality due to infectious and parasitic diseases was dominant, especially among infants and children. In the latter part of the century, there was a shift to mortality due to chronic diseases (especially cardiovascular diseases and cancer) as primary causes of death (Omran).

Table 2 shows cause-specific mortality information for the top ten causes of death in the United States in 1998. The major cause of death was heart disease, which was the triggering cause for almost one-third of all deaths. Cancer was the main cause for almost one-quarter of all deaths. Other major killers include chronic obstructive pulmonary diseases (COPD), contributing to 7 percent of all deaths; accidents, comprised of motor vehicle and other accidents; pneumonia and influenza; diabetes; suicide; nephritis; and chronic liver disease and cirrhosis.

Some causes of death are more important at younger ages than for the total population. For example, among individuals aged fifteen to twenty-four in 1998, the top three causes of death were accidents, homicide, and suicide, respectively. Within this age group, human immunodeficiency virus (HIV) was the ninth leading cause of death. Deaths due to HIV, although still important, dropped 20.7 percent between 1997 and 1998 (Murphy).

Even though a particular disease may represent a large portion of all deaths, its elimination does not assure huge gains in life expectancy. On the contrary, it may result in only modest life expectancy increases, a phenomenon called "The Taeuber Paradox" (Taeuber). For example, even though cancer represents about one-quarter of all deaths, its elimination would add only two to three years to life expectancy at birth (Keyfitz). This paradox results because most cancer deaths occur at older ages; thus, preventing or curing this one disease provides an opportunity for death to occur from other diseases.

Longer lives and better health

A crucial question is whether individual lives are increasing in length and quality: are people not only living longer, but enjoying additional years of health and functional ability, or are they experiencing more chronic conditions and physical disability? Fortunately, most recent research suggests that individuals are enjoying longer years with better health (see Rogers, Rogers, and Belanger). However, there are also race/ethnic differences in this relationship, such that African-Americans and Native Americans live many of these additional years in poor health (Hayward and Heron).

Factors related to mortality

A large range of factors exert strong impacts on the prospects of longevity, including social, economic, cultural, psychological, biological, public health, and medical characteristics. The public health and medical communities have reduced or prevented many infectious diseases: diphtheria, measles, and typhoid fever have declined substantially, and smallpox has been eradicated (Link and Phelan). Biomedical interventions have prolonged life through such developments as pharmaceuticals, surgery, transplants, and other technological developments.

Biological research has also taught us more about genetically linked diseases. The methods of recombinant DNA have led to the familial tracking of cancer genes, including breast cancer; to the tracking from person to person of infections, including HIV and tuberculosis; and to the detection of both viral and genetic components in insulin-dependent diabetes (Susser and Susser). New developments uncovered by the human genome project promise future increases in life expectancy.

Health behaviors also influence longevity. Cigarette smoking is considered the single most important preventable determinant of mortality in developed nations. Cigarette smokers experience a mortality gradient: as the number of cigarettes smoked increases, the risk of death increases. The immense mortal effects of cigarette smoking in U.S. society will continue through much of this century, with literally millions of lives prematurely lost due to cigarette smoking (Nam et al.).

Heavy alcohol use also increases the risk of death via accidents and violence and through certain organic diseases. However, moderate drinking has been shown to have a beneficial effect on health and survival from circulatory diseases (Rogers et al., 2000). Some studies have shown other health behaviors, particularly exercise frequency, to be related to mortality risk. Even as we identify behavioral risk factors, individual habits are often so deeply entrenched that knowledge of this increased risk does not always motivate change. For example, even though obesity is known to increase the risk of death, the prevalence of obesity in the general population has been increasing.

Socioeconomic status can increase longevity by providing both knowledge about health risks and ways to avoid them, and the means with which to manage risks and undergo treatment (Link and Phelan). High socioeconomic status is often coupled with beneficial health behaviors. Other important factors that increase longevity include favorable social ties—to family, friends, and the community; stable mental health; and religious involvement.

Implications of past and future longevity

Increased longevity has affected kin ties, retirement, the population age distribution, and overall population size (White and Preston). Added years of life increase opportunities to accumulate life experiences, complete or change roles, extend relationships with others, and increase the potential for rich and complex social networks. Indeed, kinship, friendship, and community networks can be extended and expanded (Riley). Unlike earlier time periods, children born today can expect to survive into young adulthood with all of their siblings, parents, and grandparents. Moreover, it is increasingly common for children to know their great-grandparents and even great-greatgrandparents.

Changes are also afoot in educational and career trajectories. Because of longer lives, many individuals are going to school longer before embarking on a career, and some individuals now plan for multiple careers. Longer lives also mean that most individuals will live to see retirement and will spend a substantial number of years in retirement. These changes abet further change; for example, some retired individuals decide to return to the labor force.

The population age distribution is also changing. In previous centuries, the U.S. age structure resembled a pyramid, with large numbers of individuals at the youngest ages and few individuals at the oldest ages. Today, the distribution approximates a pillar, with similar numbers of individuals in each age. Although there are advantages to this new age distribution, there are also potential disadvantages. For instance, because there is a lower proportion of people in the working years to contribute to Social Security, and a higher proportion of Social Security recipients, the basic age requirement for Social Security is gradually increasing from sixty-five to sixty-seven years of age.

Future trends in life expectancies

Few researchers assert that there will be no future mortality improvement. Although there have been periodic setbacks in life expectancy increases, say, with AIDS, such setbacks are usually of short duration and are compensated for by later improvements in controlling and treating infectious diseases and by further improvements in other causes of death. Thus, the question is not whether mortality will improve in the future, but by how much it will improve, and what age, sex, race/ethnic, and socioeconomic status groups will reap the greatest improvements. Overall, continued changes in health behavior, developments in medical technology, and improved quality of life bode for a generally bright future, most likely with steady increases in average length of life accompanied by an increasingly healthy population.

Richard G. Rogers Robert A. Hummer

See also Life Expectancy; Life Span Extension; Longevity: Reproduction; Longevity: Selection; Population Aging.

BIBLIOGRAPHY

Anderson, R. N. "United States Life Tables, 1998." National Vital Statistics Reports 47 (2001): 1–38.

Fries, J. F. "Aging, Natural Death, and the Compression of Morbidity." New England Journal of Medicine 303 (1980): 130–135.

Hayward, M. D., and Heron, M. "Racial Inequality in Active Life among Adult Americans." Demography 36 (1999): 77–91.

Keyfitz, N. "What Difference Would it Make if Cancer Were Eradicated? An Examination of the Taeuber Paradox." Demography 14 (1977): 411–418.

Link, B. G., and Phelan, J. "Social Conditions as Fundamental Causes of Disease." Journal of Health and Social Behavior Extra Issue (1995): 80–94.

Murphy, S. L. "Deaths: Final Data for 1998." Monthly Vital Statistics Report 48 (2000): 1–108.

Nam, C. B.; Rogers, R. G.; and Hummer, R. A. "Impact of Future Cigarette Smoking Scenarios on Mortality of the Adult Population in the U.S., 2000–2050." Social Biology 43 (1996): 155–168.

National Research Council. Between Zeus and the Salmon: The Biodemography of Longevity. Edited by K. Wachter and C. Finch. Washington, D.C.: National Academy Press, 1997.

Olshansky, S. J.; Carnes, B. A.; and Cassel, C. "In Search of Methuselah Estimating the Upper Limits to Human Longevity." Science 250 (1990): 634–640.

Omran, A. R. "The Epidemiologic Transition: A Theory of the Epidemiology of Population Change." Milbank Memorial Fund Quarterly 49 (1971): 509–538.

Riley, M. W. Aging in the Twenty-first Century. Boettner Lecture, 1990. Bryn Mawr, Pa.: Boettner Research Institute, 1991.

Rogers, R. G.; Hummer, R. A.; and Nam, C. B. Living and Dying in the USA: Social, Behavioral, and Health Differentials in Adult Mortality. New York: Academic Press, 2000.

Rogers, R. G.; Rogers, A.; and Belanger, A. "Active Life among the Elderly in the United States: Multistate Life-table Estimates and Population Projections." The Milbank Quarterly 67 (1989): 370–411.

Rogers, R. G.; Hummer, R. A.; Nam, C. B.; and Peters, K. D. "Demographic, Socioeconomic, and Behavioral Factors Affecting Ethnic Mortality by Cause." Social Forces 74 (1996): 1419–1438.

Susser, M., and Susser, E. "Choosing a Future for Epidemiology: I. Eras and Paradigms." American Journal of Public Health 86 (1996): 668–673.

Taeuber, C. "If Nobody Dies of Cancer." Kennedy Institute Quarterly Report 2 (1976): 6–9.

White, K. M., and Preston, S. H. "How Many Americans are Alive Because of Twentieth-Century Improvements in Mortality?" Population and Development Review 22 (1996): 415–429.

Wilmoth, J. R., and Lundstrom, H. "Extreme Longevity in Five Countries: Presentation of Trends with Special Attention to Issues of Data Quality." European Journal of Population 12 (1996): 63–93.

LONGITUDINAL STUDY

See Panel study; Physiological changes; Surveys