To some degree, the U.S. began to move away from understanding illness and disease as a collective problem, because social interventions were almost too successful. In the first half of the 20th century, innovations—including improved sanitation and the advent of new vaccines and antibiotics—led to infectious disease mortality plummeting. Between 1900 and 1950, U.S. deaths from major infectious killers fell by more than 90%. With the great infectious threats receding, researchers turned toward chronic disease. Epidemiologists quickly identified correlations between behaviors, including smoking, diet, and physical activity, and conditions like heart disease and cancer, helping to launch what later historians called “risk factor” epidemiology.
The most influential of these efforts, the Framingham Heart Study, began in 1948 by recruiting ordinary residents of a Boston suburb to undergo regular examinations. The study followed more than 5,000 residents for decades, tracking their diets, habits, medical histories, and physical exams to identify the factors that predicted heart disease. Over time, the study’s reports emphasized “modifiable risk factors,” such as smoking, high blood pressure, and physical inactivity. These findings helped to enshrine the idea that chronic illness was best understood as a byproduct of individual behavior—even though the Framingham study also documented socioeconomic and environmental factors that influenced heart disease.
Health education campaigns adopted this vocabulary, urging Americans to adopt better habits to boost their well-being. A typical mid-century health education pamphlet instructed Americans to prevent heart disease by quitting smoking, reducing fat intake, and exercising regularly. This advice sidelined environmental constraints like housing and work conditions, which also influenced people’s health. The Cold War political culture helped shape the new epidemiology and reinforced its emphasis on Americans getting in shape. Presidents and policymakers promoted bodily discipline as a civic virtue, warning of a nation weakened by sedentary habits and “softness.” One widely distributed 1960s filmstrip, The Smoking Machine, showed a clear plastic lung turning black as a motor pumped cigarette smoke into it—an iconic demonstration that taught children that disease was the direct result of individual behavior. The President’s Council on Physical Fitness cast exercise as both a healthy behavior and a patriotic obligation, linking the disciplined body to the national strength necessary to defeat the Soviet Union.
Taking their cues from the political climate, public health agencies adopted this way of thinking as well. By the 1970s, the Department of Health, Education, and Welfare’s Healthy People initiative framed chronic disease as a problem that could be solved by Americans modifying their personal habits, treating lifestyle change as the central strategy for prevention. Emphasizing personal behavior allowed public health agencies to promote action without confronting powerful economic interests or demanding large-scale economic redistribution.