Long-term recreational physical activity and breast cancer in the National Health and Nutrition Examination Survey I epidemiologic follow-up study.

Our purpose was to study the association between long-term recreational physical activity and breast cancer in the Epidemiological Follow-up Study (NHEFS) of the first National Health and Nutrition Examination Survey (NHANES I, 1971-1975). The analytic cohort included 6160 women who were free of breast cancer at the first NHEFS follow-up in 1982-1984 and had interview data on recreational physical activity (low, moderate, and high) in 1982-1984 and 10 years earlier, in 1971-1975. We created categories of long-term (1982-1984 + 1971-1975) recreational physical activity: (a) consistently low; (b) moderate/inconsistent; and (c) consistently high. Data were analyzed using Cox proportional hazard regression models. A total of 138 women developed breast cancer between 1982-1984 and 1992. In women > or =50 years of age in 1982-1984, consistently high (versus consistently low) recreational physical activity was associated with a 67% reduction in breast cancer risk (n = 96 cases; relative risk, 0.33; 95% confidence interval, 0.14-0.82; P for trend = 0.03); in women <50 years of age (n = 42 cases), there was no association. Associations were not modified by body mass index or by weight gain as an adult. High recreational physical activity over the long-term may reduce breast cancer risk in women > or =50 years of age; in this sample, it did so regardless of weight history.