Policy ForumDemography

Broken Limits to Life Expectancy

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Science  10 May 2002:
Vol. 296, Issue 5570, pp. 1029-1031
DOI: 10.1126/science.1069675

Is life expectancy [HN1] approaching its limit? Many—including individuals planning their retirement and officials responsible for health and social policy—believe it is. The evidence suggests otherwise.

Consider first an astonishing fact. Female life expectancy in the record-holding country has risen for 160 years at a steady pace of almost 3 months per year [Fig. 1 and suppl. table 1 (1)]. In 1840 the record was held by Swedish women, who lived on average a little more than 45 years. Among nations today, the longest expectation of life—almost 85 years—is enjoyed by Japanese women [HN2]. The four-decade increase in life expectancy in 16 decades is so extraordinarily linear [r2 = 0.992; also see suppl. figs. 1 to 5 (1)] that it may be the most remarkable regularity of mass endeavor ever observed. Record life expectancy has also risen linearly for men (r2 = 0.980), albeit more slowly (slope = 0.222): the gap between female and male levels [HN3] has grown from 2 to 6 years (suppl. Fig. 2).

Fig. 1.

Record female life expectancy from 1840 to the present [suppl. table 2 (1)]. The linear-regression trend is depicted by a bold black line (slope = 0.243) and the extrapolated trend by a dashed gray line. The horizontal black lines show asserted ceilings on life expectancy, with a short vertical line indicating the year of publication (suppl. table 1). The dashed red lines denote projections of female life expectancy in Japan published by the United Nations in 1986, 1999, and 2001 (1): It is encouraging that the U.N. altered its projection so radically between 1999 and 2001.

In addition to forewarning any looming limit to the expectation of life, trends in best-practice life expectancy provide information about the performance of countries. The gap between the record and the national level is a measure of how much better a country might do at current states of knowledge and demonstrated practice. Although rapid progress in catch-up periods typically is followed by a slower rise, life-expectancy trajectories do not appear to be approaching a maximum (Fig. 2).

Fig. 2.

Female life expectancy in Chile, Japan, New Zealand (non-Maori), Norway, and the United States compared with the trend in record life expectancy.

The linear climb of record life expectancy suggests that reductions in mortality should not be seen as a disconnected sequence of unrepeatable revolutions but rather as a regular stream of continuing progress (2, 3). Mortality improvements [HN4] result from the intricate interplay of advances in income, salubrity, nutrition, education, sanitation, and medicine, with the mix varying over age, period, cohort, place, and disease (4). Before 1950, most of the gain in life expectancy was due to large reductions in death rates at younger ages. In the second half of the 20th century, improvements in survival after age 65 propelled the rise in the length of people's lives. For Japanese females, remaining life expectancy at age 65 grew from 13 years in 1950 to 22 years today, and the chance of surviving from 65 to 100 soared from less than 1 in 1000 to 1 in 20 (1). The details are complicated but the resultant straight line of life-expectancy increase is simple.

World life expectancy more than doubled over the past two centuries, from roughly 25 years to about 65 for men and 70 for women (4). This transformation of the duration of life greatly enhanced the quantity and quality of people's lives. It fueled enormous increases in economic output and in population size, including an explosion in the number of the elderly [HN5] (5, 6). Although students of mortality eventually recognized the reality of improvements in survival, they blindly clung to the ancient notion that under favorable conditions the typical human has a characteristic life-span. As the expectation of life rose higher and higher, experts were unable to imagine its rising much further. They envisioned various biological barriers and practical impediments. The notion of a fixed life-span evolved into a belief in a looming limit to life expectancy.

Ultimate Expectations of Life

In 1928, Louis Dublin quantified this consensus (7). Using U.S. life tables as a guide, he estimated the lowest level to which the death rate in each age group could possibly be reduced. His calculations were made “in the light of present knowledge and without intervention of radical innovations or fantastic evolutionary change in our physiological make-up, such as we have no reason to assume.” His “hypothetical table promised an ultimate figure of 64.75 years” for the expectation of life both for males and for females. At the time, U.S. life expectancy was about 57 years. Because Dublin did not have data for New Zealand, he did not realize that his ceiling had been pierced by women there: in the non-Maori life table for 1921, female life expectancy is 65.93 years [Fig. 1 and suppl. tables 1 and 2 (1)].

Marshalling methods and arguments strikingly similar to Dublin's, Olshansky et al. in 1990 and again in 2001 [HN6] assess the life expectancy that could be attained if age-specific death rates could be reduced by amounts that are not “implausible,” “overly optimistic,” and “highly unlikely” (8, 9). In 1990, they asserted that life expectancy “should not exceed … 35 years at age 50 unless major breakthroughs occur in controlling the fundamental rate of aging.” This cap, however, was surpassed by Japanese females in 1996.

Other scholars tried various stratagems to seize life expectancy heights that they could not conceive of being surmounted (1). Although some of the more recent ostensible limits have not yet been exceeded, those from Dublin in 1928 to Olshansky et al. in 1990 have been broken, on average 5 years after publication (Fig. 1 and suppl. table 1).

Better Forecasts

The ignominious saga of life-expectancy maxima is more than an exquisite case for historians intrigued by the foibles of science. Continuing belief in imminent limits is distorting public and private decision-making. Forecasts of the expectation of life [HN7] are used to determine future pension, health-care, and other social needs. Increases in life expectancy of a few years can produce large changes in the numbers of the old and very old, substantially augmenting these needs (5, 6). The officials responsible for making projections have recalcitrantly assumed that life expectancy will increase slowly and not much further (10). The official forecasts distort people's decisions about how much to save and when to retire. They give politicians license to postpone painful adjustments to social-security and medical-care systems (11).

Officials charged with forecasting trends in life expectancy over future decades should base their calculations on the empirical record of mortality improvements over corresponding spans of the past (2, 3). Because best-practice life expectancy has increased by 2.5 years per decade for a century and a half, one reasonable scenario would be that this trend will continue in coming decades. If so, record life expectancy will reach 100 in about six decades. This is far from eternity: modest annual increments in life expectancy will never lead to immortality. It is striking, however, that centenarians may become commonplace within the lifetimes of people alive today (12).

Life expectancy can be forecast by considering the gap between national performance and the best-practice level (Fig. 2). The U.S. disadvantage varied from a decade in 1900 to less than a year in 1950 and about 5 years in 2000 (Fig. 2). If the trend in record life expectancy continues and if the U.S. disadvantage is between a year and a decade in 2070, then female life expectancy would be between 92.5 and 101.5, considerably higher than the Social Security Administration's forecast of 83.9 published in 1999 (1). An alternative method for forecasting life expectancy is to analyze the rapidity of improvement in age-specific death rates over many decades and then to use this information to project death rates over coming decades (2, 3). The official Japanese forecast, issued in 1997, of life expectancy (for males and females combined) in 2050 is 82.95 (1). Projections based on the decline in death rates in Japan since 1950 result in a life expectancy some 8 years longer, 90.91, with a 90% confidence range from 87.64 to 94.18 (3).

Declines in mortality might be systematically slower than in the past. On the other hand, biomedical research may yield unprecedented increases in survival. Given the extraordinary rise in best-practice life expectancy and the demonstrated nearsightedness of expert vision, the central forecast should be based on the long-term trend of sustained progress in reducing mortality.

In their quest to impose a cap on average longevity, students of mortality ignored essential research questions. Major changes in life expectancy hinge on improvements in survival at advanced ages, but comprehensive analysis of the substantial reductions since the mid-20th century in death rates after age 80 first flourished in the 1990s (1, 13). Hypothesized biological barriers to longer life-spans also first received systematic attention (and refutation) a decade ago (1, 1416). The impact of continuing mortality improvements on life expectancy attracted empirical (12) and theoretical attention (17) in the late 1980s, with refined methods developed over the past decade (13).

Three Findings

This mortality research has exposed the empirical misconceptions and specious theories that underlie the pernicious belief that the expectation of life cannot rise much further. Nonetheless, faith in proximate longevity limits endures, sustained by ex cathedra pronouncement and mutual citation (1, 8, 9). In this article we add three further lines of cogent evidence. First, experts have repeatedly asserted that life expectancy is approaching a ceiling: these experts have repeatedly been proven wrong. Second, the apparent leveling off of life expectancy in various countries is an artifact of laggards catching up and leaders falling behind. Third, if life expectancy were close to a maximum, then the increase in the record expectation of life should be slowing. It is not. For 160 years, best-performance life expectancy has steadily increased by a quarter of a year per year, an extraordinary constancy of human achievement.

HyperNotes Related Resources on the World Wide Web

General Hypernotes

Dictionaries and Glossaries

The Glossary of Population Terms, made available by the Population Reference Bureau, includes definitions of concepts related to demographics, mortality, and life expectancy.

The United Nations Population Information Network offers a Dictionary of Demographic and Reproductive Health Terminology.

Web Collections, References, and Resource Lists

The Open Directory Project has compiled links to Internet resources on demography and population studies.

The Max Planck Institute for Demographic Research site features a selection of demography links.

The Web site of the Population Reference Bureau, a nonprofit provider of worldwide information on population and demographics, offers general information on population trends, mortality, and a wealth of other topics. The Bureau's PopNet browser organizes a comprehensive set of population-related links by institution, country, and topic.

The International Programs Center of the U.S. Census Bureau offers a searchable International Data Base (IDB) of population and demographic information and projections (including mortality and life expectancy data).

The World Wide Web Virtual Library on Demography and Population Studies points to a variety of Internet resources on demographic data sources and information.

H-DEMOG, the Web site of the Historical Demography Internet discussion group, includes a page of links to demography Web resources.

The Population Studies Center at the University of Michigan maintains a collection of Internet resources on issues of demographics, aging, mortality, and population.

The Sharlin Demography Library of the U.C. Berkeley Department of Demography offers a convenient list of pointers to demography Web resources.

The Population & Environment Linkages Service, hosted by the National Council for Science and the Environment, provides links to information (much of it culled from the International Data Base of the U.S. Census Bureau) on worldwide demographics, current and projected life expectancy values, and health policy.

The Center for Human Resource Research at Ohio State University offers a collection of Internet Resources for Demographers.

The Netherlands Interdisciplinary Demographic Institute provides the World Wide Web of Demography, a wide-ranging collection of online resources.

General Reports and Articles

The Population Index Web site, from Princeton University's Office of Population Research, provides a searchable and browsable database containing more than 45,000 abstracts of demographic literature published since 1986.

Population Handbook [PDF], a general introduction to population dynamics and demographic data from the Population Reference Bureau, includes sections explaining life tables, life expectancy, and mortality rates.

Between Zeus and the Salmon: The Biodemography of Longevity, from the Committee on Population of the National Research Council, examines “what biology and demography have to tell and ask each other about human longevity,” and touches upon some of the themes explored in this policy forum.

Longevity Records, a study of the life spans of a variety of fish, reptile, amphibian, bird, and mammal species (including Homo sapiens), is made available online at the Max Planck Institute for Demographic Research site. Also posted at the institute site is an online edition of Exceptional Longevity: From Prehistory to the Present, a monograph exploring the evolution of human longevity over time.

“Biodemographic trajectories of longevity,” a review article by J. W. Vaupel et al. in the 8 May 1998 issue of Science, explores the possible causes of the substantial increase in old-age survival since 1950.

Demographic Research is a free, peer-reviewed online journal published by the Max Planck Institute for Demographic Research.

Population Today is a newsletter posted by the Population Reference Bureau.

Numbered Hypernotes

1. Life expectancy. A wide range of Web sites (in addition to the supporting online material accompanying this policy forum) provide basic data on worldwide life expectancy. Among them: The Berkeley Mortality Database, developed by J. R. Wilmoth, offers life tables, birth and death rate data, and historical life expectancy figures for France, the U.S., Sweden, and Japan, drawn from census data and vital statistics. The National Center for Health Statistics of the U.S. Centers for Disease Control and Prevention publishes historical life expectancy data for the United States. Statistics Canada maintains current and historical information about life expectancy at birth by gender and province. The World Population Data Sheet of the Population Reference Bureau presents global data on current life expectancy by country and gender. The Global Terrestrial Observing System (GTOS) of the U.N. Food and Agriculture Organization offers a capsule summary [PDF] of the concept of life expectancy and the principal sources for worldwide data. An article posted by the Population Reference Bureau titled “How much better can it get?” briefly outlines the debate between researchers who argue for and against fundamental biological limits on human life expectancy.

2. Life expectancy in Japan. Data on Japanese life expectancy can be found in the database pages of the Japanese Ministry of Health, Labor, and Welfare, which offer detailed life tables for Japan, along with information on historical trends in the five leading causes of death and other information. Japanese government predicitions of the country's future population, along with the life expectancy assumptions that those predictions embody, can be downloaded at the Web site of the National Institute of Population and Social Security Research.

3. Differences between female and male life expectancy. In The World's Women 2000: Trends and Statistics, the United Nations Statistics Division provides a worldwide summary table of life expectancy and infant mortality for females and males. Historical data on life expectancy by age for males and females in the U.S., covering the period from 1850 to 1999, can be found on the InfoPlease site. “Around the globe, women outlive men,” an article from the August/September 2001 issue of Population Today, offers a color-coded global map of differences between male and female longevity and some notes on the reasons for the difference; another article from the Population Reference Bureau discusses the causes of the gender gap in U.S. mortality.

4. Mortality and mortality improvements. The National Academy Press publication Beyond Six Billion: Forecasting the World's Population includes a chapter on mortality that explores the causes of historical increases in mortality and of the differences in mortality increase between different societies. World Population Beyond Six Billion, a report presented by the Population Reference Bureau, discusses in some detail the long-term changes in population patterns since before 1900 and the nature and causes of historical mortality declines.

5. Implications of an aging population. Institutions focused on the demography of aging include (among many others) the National Institute on Aging, the Administration on Aging of the U.S. Department of Health and Human Services, the University of Pennsylvania's Population Aging Research Center, and the Michigan Center on the Demography of Aging. Several publications of the National Academy Press, including Preparing for an Aging World (2001) and Demography of Aging (1994), deal with the aging of the worldwide population from demographic and policy perspectives. A 10 March 2001 article in Science News titled “Making sense of centenarians” describes the increase in 100-plus-year-old members of the population, and the lifestyle, health, and genetic factors that may be contributing to that increase. Aging in the Americas into the XXI Century, a wall chart offered in PDF form from the National Institute on Aging and the U.S. Census Bureau, provides graphic information on the changing age structure in North, Central, and South America and the implications of those changes. The Population Reference Bureau has posted a variety of reports and articles on the older population, including Elderly Americans, a study that overviews the demographic characteristics and profound social, health, and economic impacts of the rapidly aging population in the U.S.

6. Previous discussion in Science. The issue of whether there are limits to life expectancy has a long pedigree of discussion in Science. In the 2 November 1990 issue, S. J. Olshansky, B. A. Carnes, and C. Cassel published “In search of Methuselah: Estimating the upper limits to human longevity,” which argued that fundamental limits to life expectancy are likely (AAAS members can gain access to the full text of that article through the JSTOR link on the membership portal AAASmember.org). J. R. Wilmoth, in “The future of human longevity: A demographer's perspective” in the 17 April 1998 issue, held that extrapolation of the long-term, stable declines in mortality suggested a continued rise in life expectancy, an assertion disputed in subsequent letters by L. Gavrilov and N. Gavrilova and by S. J. Olshansky et al. “Prospects for Human Longevity,” a Policy Forum by S. J. Olshansky, B. A. Carnes, and A. Désesquelles published in the 23 February 2001 issue, once again argued for fundamental biological limits to human life span; that article was discussed in a letter exchange with R. Lee.

7. Life expectancy forecasts. The World Population Prospects Population Database of the United Nations Population Information Network lets users query the U.N.'s international forecasts for a variety of population indicators, including life expectancy and percent of population in various age cohorts, through 2050. A document presenting the results of the 1996 population projection, provided by the Austria-based International Institute for Applied Systems Analysis, includes a discussion of the assumptions about mortality that factor into such estimates. World Population Futures, presented by the Population Reference Bureau, provides a thorough and useful overview of how future population is forecast and, in particular, of the uncertainties involved in projections of future mortality and life expectancy.

8. J. Oeppen is with the Cambridge Group for the History of Population and Social Structure, Department of Geography, University of Cambridge, and is associated with the Max Planck Institute for Demographic Research.

9. J. W. Vaupel is at the Max Planck Institute for Demographic Research.

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