Some nations experienced more than a doubling of average life expectancy during the 20th century. Life expectancy at birth in Japan now approaches 82 years, the highest level among the world’s more developed countries, and life expectancy is at least 79 years in several other more developed countries.
Less developed regions of the world have experienced a steady increase in life expectancy since World War II, with some exceptions in Latin America and more recently in Africa, the latter due to the impact of the HIV/AIDS epidemic. The most dramatic gains have occurred in East Asia, where life expectancy at birth increased from less than 45 years in 1950 to more than 72 years today.
Changes in life expectancy reflect a health transition occurring around the globe at different rates and along different paths. This transition is characterized by a broad set of changes that includes:
- A shift from high to low fertility;
- A steady increase in life expectancy at birth and at older ages; and
- A shift from the predominance of infectious and parasitic diseases to the growing impact of noncommunicable diseases and chronic conditions.
The health transition shifts the human survival curve so that the chances of surviving another year are higher at every age. In early nonindustrial societies, the risk of death was high at every age, and only a small proportion of people reached old age. In modern survival curves for industrialized societies, most people live past middle age, and deaths are highly concentrated at older ages. Figure 3 depicts the evolution of survival for White females in the United States from 1901 to 2003. In most countries, the curve shifts to the right as longevity increases.
Increases in the probability of survival raise questions about limits to life expectancy and the potential for human lifespan. Despite assertions that life expectancy must be approaching a limit, data on female life expectancies from 1840 to 2000 show a steady increase of 3 months per year (Figure 4). The country with the highest average life expectancy has varied over time—in 1840 it was Sweden, and today it is Japan—but the linearity of the pattern (also seen for males) is remarkable. While HIV/AIDS, obesity, and similar trends may temper expectations for continued increases in longevity, several findings encourage a more optimistic outlook. These include:
- Studies showing that death rates at very old ages level off or decline;
- The explosion in the number of centenarians worldwide;
- The finding that, even at older ages, mortality rates are malleable and amenable to social interventions; and
- Evidence that medical advances and new drugs are increasing life expectancy.
Recent research raises other questions about the future of life. Researchers have been able to experimentally increase lifespan in insects and animals through gene insertion, caloric restriction, and diet. It remains to be seen whether similar increases can be replicated in humans.
Source: Glover J. United States Life Tables, 1890, 1901, 1910, and 1901-1910. Washington: Bureau of the Census, 1921. Available at: http://www.cdc.gov/nchs/data/lifetables/life1890-1910.pdf;  and Arias E. United States Life Tables, 2003. National Vital Statistics Report: 2006;54(14):1-40. Available at: http://www.cdc.gov/nchs/data/nvsr/nvsr54/nvsr54_14.pdf .
Figure 4: HIGHEST NATIONAL LIFE EXPECTANCY AT BIRTH: 1840-2000 - Life expectancy in years (graph)
No data available. Graph of age (x-axis) by decade (y-axis) shows life expectancy for men and women increasing on straight lines sloped at roughly 45 degrees, with women's life expectancy increasing at a slightly greater rate than men's.
Source: Adapted from Oeppen J, Vaupel JW. Broken Limits to Life Expectancy. Science. 2002;296;1029-1031.