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In the course of human history, life expectancy at birth has increased from around 20-30 years during prehistoric times to 75-80 years in many low-mortality countries today. Nearly half of this increase has taken place during the twentieth century. The highest life expectancy has been recorded in Japan, a developed country where health improvements in the early part of the twentieth century lagged behind those of European countries, but where mortality declines have been particularly impressive since the 1950s. Life expectancy at birth in Japan reached 84.6 years for women and 77.6 years for men by the year 2000. Moreover, the United Nations’ estimates show an average life expectancy of 74.8 years in the more developed regions of the world, with 56 percent of industrialized countries having life expectancies of over 75 years in 1995-2000. The lowest life expectancies in industrialized countries are found in Eastern Europe and the former Soviet Union, where health conditions stagnated during the late twentieth century, particularly for adult men.
By the middle of the twentieth century, life expectancy in the less developed regions of the world had reached 40.9 years and it had further increased to 62.5 years by the end of the century according to the United Nations’ estimates. These gains are impressive and suggest that life expectancy more than doubled between 1900 and 2000 in most parts of the developing world. As a result, the gap in average life expectancy between more and less developed regions has narrowed over time – from about 26 years in 1950-5 to about 11 years in 19952000. The mortality decline in developing countries, however, has not been uniform, and the slower pace of improvement in the least developed regions relative to others has led to a greater disparity among developing countries over time. Estimates show an average life expectancy of only about 50 years in Africa, with only 21 percent of African countries having estimated life expectancies of 60 years or more. In contrast, the average life expectancy was estimated to be around 69 years in Latin America, with 64 percent of Latin American countries having life expectancies of 70 years or more.
The epidemiologic transition, a shift from infectious diseases to chronic degenerative diseases as leading causes of death, has been instrumental in shaping trends in human mortality and the age pattern of mortality decline. The fall in death rates from infectious diseases led to significant improvements in the survival chances of infants and young children and was largely responsible for the rise in life expectancy in the late nineteenth and early twentieth centuries in industrialized countries, and during the second half of the twentieth century in less developed regions of the world. These reductions in infant and child mortality, together with a decline in fertility, have contributed to a shift in the population age distribution toward an older population in both developed and developing countries. As a result, chronic degenerative diseases have become more common and today represent an ever-increasing percentage of all deaths even as adult mortality has continued to decline in most places. Future gains in life expectancy in industrialized nations will thus largely depend on trends in mortality from such leading chronic diseases as heart disease and cancer at older ages.
Many less developed countries have experienced an epidemiologic transition characterized by overlapping eras whereby chronic diseases of middle and older ages have become more common as populations have aged, at the time that childhood infectious diseases have continued to create a major health burden among the poor. The emergence of HIV/AIDS and drug-resistant varieties of tuberculosis and malaria is perhaps the best example of the continued impact of infectious diseases on mortality.
Many factors have influenced the mortality trends discussed above, including improvements in living standards, public health measures, cultural and behavioral factors, modern medical technologies, and the actions of governments and international agencies and organizations. Most notably, much of the mortality reduction at older ages in the latter decades of the twentieth century was due to decline in death rates from cardiovascular diseases. In addition, behavioral changes, most importantly reductions in smoking, have contributed to mortality decline, especially among men.
- Omran, A. R. (1971) The epidemiologic transition: a theory of the epidemiology of population change. Milbank Memorial Fund Quarterly 49 (4): 509-37.
- Preston, S. H. (1995) Human mortality throughout history and In: Simon, J. L. (ed.), The State of Humanity. Blackwell, Cambridge, MA, pp. 30-6.
- United Nations (1999) Health and Mortality Issues of Global Concern. United Nations, New York.