An important distinction to be made when discussing aging and longevity is between life expectancy and lifespan. Life expectancy refers to the number of years a person can be expected to live, based on the statistical average. This statistical average is calculated based on an overall population, often beginning from the time of birth, and includes those who die during or shortly after childbirth, those who die during adolescence and adulthood, and those who live well into old age. The average life expectancy for a man in the United States today is 76.4 years; for a woman, it’s 81.2 years.

Lifespan, on the other hand, is the number of years that any particular individual lives. Leonard Nimoy had a lifespan of 83 years, for example. The maximum number of years that any known person has lived is 122 years. Therefore, 122 is sometimes cited as the maximum human lifespan, although that will change as soon as someone lives longer.

Life expectancy has increased dramatically over the twentieth century. In 1900, life expectancy for a man was 46 years. Today, as you read above, a man’s life expectancy is more than 76 years. Statistics like these can be a source of confusion. This does not mean that, in 1900, most men dropped dead at age 46. The greatest difference between then and now is the change in the frequency of infant mortality, with many fewer children dying as a result of infectious and communicable diseases. Because those deaths are included in the calculation of the average life expectancy, they greatly affect the overall measure. Decreases in infant mortality occurred because of improvements in sanitation (principally, cleaner water), which reduced the incidence of communicable diseases like cholera, and the availability of vaccines to prevent diseases such as smallpox, polio, and measles.

495

For those surviving to adulthood, the gains in life expectancy have been more modest over the same period: about nine additional years for women and five additional years for men. Major factors that are responsible for recent increases in the life expectancy of U.S. adults are a decrease in the prevalence of smoking and improved medical care that allows individuals who are affected with chronic diseases to live longer. During the next 25 years, two factors—longer life spans and aging baby boomers—will combine to double the population of Americans 65 years or older to about 72 million. By 2030, older adults will account for roughly 20% of the U.S. population. (INFOGRAPHIC 21.2)

Question 21.2

496

Clearly, a number of factors can influence how long a person lives. The most obvious is disease. The biggest killers today are largely chronic diseases, such as heart disease, cancer, and diabetes. Anything that increases one’s odds of getting these diseases, such as smoking or obesity, will have a correspondingly negative impact on one’s life expectancy. There are also more subtle influences. People with higher levels of education have a higher life expectancy than those with lower levels. Decreased life expectancy is also associated with being unmarried, low socioeconomic status, and being part of some racial groups.