Longevity: Social Aspects

Life expectancy changes are affected by trends in specific causes of death. Through the early part of the twentieth century, mortality due to infectious and parasitic diseases was dominant, especially among infants and children. In the latter part of the century, there was a shift to mortality due to chronic diseases (especially cardiovascular diseases and cancer) as primary causes of death (Omran).

Table 2 shows cause-specific mortality information for the top ten causes of death in the United States in 1998. The major cause of death was heart disease, which was the triggering cause for almost one-third of all deaths. Cancer was the main cause for almost one-quarter of all deaths. Other major killers include chronic obstructive pulmonary diseases (COPD), contributing to 7 percent of all deaths; accidents, comprised of motor vehicle and other accidents; pneumonia and influenza; diabetes; suicide; nephritis; and chronic liver disease and cirrhosis.

Some causes of death are more important at younger ages than for the total population. For example, among individuals aged fifteen to twenty-four in 1998, the top three causes of death were accidents, homicide, and suicide, respectively. Within this age group, human immunodeficiency virus (HIV) was the ninth leading cause of death. Deaths due to HIV, although still important, dropped 20.7 percent between 1997 and 1998 (Murphy).

Even though a particular disease may represent a large portion of all deaths, its elimination does not assure huge gains in life expectancy. On the contrary, it may result in only modest life expectancy increases, a phenomenon called "The Taeuber Paradox" (Taeuber). For example, even though cancer represents about one-quarter of all deaths, its elimination would add only two to three years to life expectancy at birth (Keyfitz). This paradox results because most cancer deaths occur at older ages; thus, preventing or curing this one disease provides an opportunity for death to occur from other diseases.