Demography of longevity: past, present, and future trends.

Life expectancy at birth has roughly tripled over the course of human history. Early gains were due to a general improvement in living standards and organized efforts to control the spread of infectious disease. Reductions in infant and child mortality in the late 19th and early 20th century led to a rapid increase in life expectancy at birth. Since 1970, the main factor driving continued gains in life expectancy in industrialized countries is a reduction in death rates among the elderly. In particular, death rates due to cardiovascular disease and cancer have declined in recent decades thanks to a variety of factors, including successful medical intervention. Based on available demographic evidence, the human life span shows no sign of approaching a fixed limit imposed by biology or other factors. Rather, both the average and the maximum human life span have increased steadily over time for more than a century. The complexity and historical stability of these changes suggest that the most reliable method of predicting the future is merely to extrapolate past trends. Such methods suggest that life expectancy at birth in industrialized countries will be about 85-87years at the middle of the 21st century.