Trends in Life Expectancy

Life expectancy has been increasing, not just in industrialized societies but also around the world.

The rise in life expectancy at birth probably began before the industrial era—before national mortality statistics were first assembled in Sweden around 1750. As noted earlier, e0 was b During recent decades the two major exceptions to the worldwide increase in life expectancy have been a stagnation and even reversal of earlier progress in parts of Africa, due to the AIDS epidemic, and in parts of the former Soviet block (especially Russia) due to social disruptions and instability.

probably in the 20s during the Middle Ages and earlier. By 1750, Sweden (and probably other parts of northwestern Europe) had attained an e0 of 38, so the upward trend in longevity appears to have begun before the industrial era. Over the next century or more, there was a slow and irregular increase in life expectancy. After about 1870, however, the increase became stable and more rapid. During the first half of the twentieth century, life expectancy in industrialized countries rose quite rapidly. Since 1950, the rise in life expectancy slowed down somewhat, as illustrated in Figure 1 for France.

The cause of the earlier rapid rise in life expectancy and its subsequent deceleration is quite simple: the decline of juvenile mortality to historically very low levels. By around 1950, infant mortality in wealthy countries was in the range of 2% to 3% of births, compared to perhaps 20% to 30% historically. Since then, infant mortality has continued to decline and now stands at around a half percent of all births in the healthiest parts of the world. As babies were saved from infectious disease, their chances of survival to old age improved considerably. Once juvenile mortality was reduced substantially, improvements in life expectancy due to the reduction of mortality in this age range had to slow down, and further gains had to come mostly from mortality reductions at older ages.

The rise in life expectancy during the second half of the twentieth century was slower than during the first half simply because it depended on the reduction of death rates at older ages rather than in infancy and childhood. Put simply, saving an infant or child from infectious disease, who then goes on to live to age 70, contributes more to average life span than saving a 70-year-old from heart disease, who may live another 10 years. Thus, the deceleration in the historical rise of life expectancy is a product of the J-shaped age pattern of human mortality: high in infancy and childhood, low through adolescence and early adulthood, and then rising almost exponentially after age 30. Gains in e0 that come from reducing juvenile mortality are quite large, whereas gains due to a reduction in old-age mortality are inevitably much smaller.

A common mistake is to assert that the deceleration in the rise of e0 reflects a slowdown in progress against mortality. In fact, the reduction of death rates has changed its character in recent decades, but it has not slowed down. At older ages, the decline of mortality has accelerated since around 1970 (as discussed below). So long as the decline of old age mortality continues, life expectancy will continue to increase, driven now by the extension of life at later ages rather than by saving juveniles from premature death.

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