Anne B. Newman - The Epidemiology of Aging

Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, 130 DeSoto Street, A510 Crabtree, Pittsburgh, PA 15261, USA

Jane A. Cauley

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Activity of Daily Living

Cardiovascular Disease

National Research Council

Older Dependency Ratio

Survey of Health Aging and Retirement in Europe

United States

The age composition of the worlds population has changed dramatically during the twentieth century. These changes continue into the twenty-first century. Specifically, the size and proportion of the older population (defined as age 65 and above), especially the oldest old (defined as age 80 and above), have increased substantially and will continue to increase. The purpose of this chapter is to present a broad and general overview of current demographic trends across the world. The main source of information for the United States (US) was the Federal Interagency Forum on Aging-Related Statistics (Older Americans 2010) []. These data should be considered in light of two caveats. First, the data are based on summary statistics and it is important to keep in mind the heterogeneity in the way that people age. The population age 65 and over is large and very diverse. Second, the population that survives to 65 years of age represents only a fraction of their original birth cohort. There may be survivor bias in those who survive to older ages, especially the oldest old.

Demography is the study of the change in the size, diversity, distribution and composition of human populations over time. Demographers have identified a general progression of changes in fertility, mortality, population composition and the demographic transition. The demographic transition is a gradual process where a society moves from relatively high rates of fertility and mortality to low rates of both fertility and mortality. The demographic transition has three stages []. In the first stage, birth and death rates are high and the population grows slowly. The age pyramid for this stage has a very narrow top with few older people and the largest number of children 04 years of age. In the second stage modernization begins, especially industrialization and urbanization. Medical care and public health improves, leading to a sharp decline in death rates and longevity. Infant mortality declines, but birth rates remain high. In the final stage, death rates continue to decline but birth rates decline, population growth surges and the age pyramid becomes more rectangular. From 1900 to 1950, a steady decline in infant mortality raised the life expectancy in industrialized nations from 4550 in 1900 to 6570 in 1950. By 1950, most industrialized nations had experienced their demographic transition. For the purposes of this chapter, per the United Nations, developed countries include all countries in Europe and North America plus Japan, Australia and New Zealand. All other countries are considered developing nations.

Virtually all nations in the world are now experiencing growth in the number of residents 65 years of age, though there is considerable variability. Most developed countries have relatively high proportions of individuals 65 years of age, but the most rapid increases in the older population are in the developing world. Birth rates are also rapidly declining in many countries, including developing countries like India and China, further accelerating the shift toward an aging society. In 1950, about 5% of the worlds population was 65 years of age while about 13% was <5 years of age. By 2020, individuals who are 65 years of age or older will outnumber children who are <5 years of age. The global population 65 years of age was estimated to be 506 million in 2008, which was about 7% of the worlds population. By 2040, the world is projected to have 1.3 billion older adults, accounting for 14% of the total population. Eastern and Western Europe will have the highest populations of people 65 years of age, including about 89% who are 80 years of age (Table ). In Europe, by the year 2040, one in four individuals will be 65 years of age. In Asia, Northern Africa, the Near East and Latin America, the proportion of residents who are 65 years of age will more than double. However, it is important to point out heterogeneity within a region. For example, the population in China and India that were 65 years of age numbered 166 million in 2008, nearly one-third of the worlds total in that age group. The absolute number will increase to 551 million in 2040 (329 million in China and 222 million in India).