...difficulties of us are liable to face as we grow older are determined by our opportunities for social interaction and intimacy, by our economic and educational experiences, and by our exposure to severe social and physical stresses. We believe that a great deal of what superficially may seem like random variability in health outcomes is in fact patterned by the kinds of social and economic experiences that people confront throughout their lives. Such variability is key to understanding aging.

Social conditions help determine several health outcomes as we age. Variations in life expectancy and disability, for example, reflect differences in past social investments in the health and well-being of different groups within society. Perhaps more surprising, aging at the biological level--as indicated by measures of metabolic function, glucose metabolism, blood pressure regulation, and pulmonary function--is also correlated with social conditions.

One of the most common indicators of health and aging used in epidemiology and demography is life expectancy, a summary estimate of how long we can expect people to live in the future. Life-expectancy measures are derived from current death rates for men and women in specific age groups. The assumption is that age-specific death rates today will be applicable in the future. Because death rates historically have changed rather quickly, though, projections are not always very accurate.

Measures of life expectancy, however, are valuable when comparing countries or populations over time--especially when used to look at historical or current, not future, patterns. In the United States in 2002, life expectancy was 77.3 years at birth and 18.2 years at age 65. The latter number means that if a person survived to age 65, he or she could expect to live, on average, another 18.2 years. These summary statistics, however, hide large differences in life expectancy across gender, racial, and ethnic groups. For example, life expectancies for white women were 80.3 years at birth and 19.5 years at age 65, but for African American women those same numbers were 75.6 and 18.0. Life expectancies for black men were 68.8 years at birth and 14.6 years at age 65. For white men, they were 75.1 years at birth and 16.1 years at age 65. Thus, even a preliminary unpacking of average life expectancies of white women and African American men reveals a difference of 11.5 years at birth and about 5 years at age 65.

Equally startling are advances in life expectancy that have occurred over the last century and those predicted based on data from the last decade or two. Life expectancy in the United States increased over twenty years between 1900 and 1950, from 47.3 to 68.2, and nearly another ten years by 2000, to 76.7. If one looks at the long-term increases in life expectancy, the majority of 'added' years in the first half of the century occurred because of improvements in infant and childhood mortality, maternal mortality, and control of infectious diseases--the results of major public-health efforts at the turn of the century. (1) However, over the last several decades we have also achieved substantial gains in life expectancy for older people. Between 1980 and 2000, life expectancy for 65-year-olds rose 1.6 years. In these decades, increases were greatest for men, who gained almost two years. These added years narrowed the gender gap slightly, but women can still expect to live three years longer than men.

Living longer may be problematic, though, if the elderly spend many of those extra years disabled or suffering from chronic conditions. Ideally, we want to increase 'active' or 'disability-free' life expectancy. Scientific opinion on whether increased life expectancy would translate into increased old-age disability has evolved over time.

In the early 1980s, investigators such as James Fries anticipated "compression of morbidity" to accompany increases in life expectancy. (2) Early evidence contradicted this notion: Health surveys indicated that people were living longer, but with substantial levels of disability for many of those years. Better treatments for many diseases were saving lives, but also leaving survivors with serious disabilities. However, more positive signs have emerged over the past few decades: Eileen Crimmins reported that disability-free life expectancy improved more during the 1980s than the 1970s, (3) while some evidence suggest rates...

NOTE: All illustrations and photos have been removed from this article.



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