If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.

—Hippocrates c. 460–377 B.C.

During the twentieth century, advances in public health and medical care helped Americans to lead longer, healthier lives. Two important measures of the health of the population are infant mortality (death) rates and life expectancy at birth rates. Infant mortality rates significantly decreased and life expectancy increased by thirty years. Table 2.1 shows the decline in infant mortality between 1983 and 2001. Table 2.2 shows the long-term upward trend in life expectancy as well as recent gains—in 2001 life expectancy at birth for the total population reached a record high of 77.2 years, up from 75.4 years in 1990.

As deaths from infectious diseases declined, mortality from chronic diseases, such as heart disease and cancer, increased...