Dietary fat and postmenopausal invasive breast cancer in the National Institutes of Health-AARP Diet and Health Study cohort

Background Although ecologic association and animal studies support a direct effect of dietary fat on the development of breast cancer, results of epidemiologic studies have been inconclusive. Methods We prospectively analyzed the association between fat consumption and the incidence of postmenopausal invasive breast cancer in the National Institutes of Health-AARP Diet and Health Study, a US cohort comprising 188736 postmenopausal women who completed a 124-item food-frequency questionnaire in 1995-1996. Hazard ratios (HRs) and 95% confidence intervals (Cls) were calculated using Cox proportional hazards regression models with adjustment for energy and potential confounding factors. All statistical tests were two-sided. Results Over an average follow-up of 4.4 years, the cohort yielded 3501 cases of invasive breast cancer. The hazard ratio of breast cancer for the highest (median intake, 40.1% energy from total fat; 434 cases per 100000 person-years) versus the lowest (median intake, 20.3% energy from total fat; 392 cases per 100000 person-years) quintile of total fat intake was 1.11 (95% Cl = 1.00 to 1.24; P-trend =.017). The corresponding hazard ratio for a twofold increase in percent energy from total fat on the continuous scale was 1.15 (95% Cl = 1.05 to 1.26). Positive associations were also found for subtypes of fat (hazard ratio for a twofold increase in percent energy from saturated fat = 1.13; 95% Cl = 1.05 to 1.22; from monounsaturated fat, HR = 1.12; 95% Cl = 1.03 to 1.21; from polyunsaturated fat, HR = 1.10, 95% Cl = 1.01 to 1.20). Correction for measurement error in nutrient intakes, on the basis of a calibration substudy that used two 24-hour dietary recalls, strengthened the associations, yielding an estimated hazard ratio for total fat of 1.32 (95% Cl = 1.11 to 1.58). Secondary analyses showed that associations between total, saturated, and monounsaturated fat intakes were confined to women who were not using menopausal hormone therapy at baseline. Conclusion In this large prospective cohort with a wide range of fat intake, dietary fat intake was directly associated with the risk of postmenopausal invasive breast cancer.