Printed in U.S.A Explaining the Relation Between Education and Postmenopausal Breast Cancer

The authors examined the relation between socioeconomic status, as defined by education level, and postmenopausal breast cancer incidence using data from the National Health and Nutrition Examination Survey I Epidemiologic Followup Study. Female participants in the study were followed from 1971-1974 to 1992-1993. Cox proportional hazards modeling was used to determine the relation between breast cancer incidence and education level. There was a direct dose-response association between education level and postmenopausal breast cancer risk. Several breast cancer risk factors, including height and reproductive-related risks such as nulliparity, were found to mediate this relation. Adjustment for these factors reduced, but did not eliminate, the positive relation between education level and risk of postmenopausal breast cancer; however, the association was no longer statistically significant. The association between higher education and increased risk of breast cancer appears to be largely explained by differences in the known risk factors for breast cancer. Am J Epidemiol 1997; 145:366-72. breast neoplasms; education; socioeconomic factors Unlike most other illnesses, breast cancer has been associated with higher socioeconomic status. This cor-relation has appeared at both the individual and the community level. Case-control studies in the United States, Canada, and Israel (1, 2) indicate that women with more than 12 years of education have a signifi-cantly increased risk of breast cancer. In a Canadian study (3), education was not related to breast cancer risk, but cases tended to have greater family incomes than controls. A number of ecologic analyses of US data (4-9) have found higher rates of breast cancer incidence and mortality among women living in more affluent communities. Smaller, individual-level stud-ies (10-15) have suggested the same disparity. Re-search in countries as diverse as Brazil (16), Finlan