To assess more precisely the relative risks associated with established risk factors for breast cancer, and whether the association between dietary fat and breast cancer risk varies according to levels of these risk factors, we pooled primary data from six prospective studies in North America and Western Europe in which individual estimates of dietary fat intake had been obtained by validated food-frequency questionnaires. Based on information from 322,647 women among whom 4,827 cases occurred during follow-up: the multivariate-adjusted risk of late menarche (age 15 years or more compared with under 12) was 0.72 (95 percent confidence interval [CI] = 0.62-0.82); of being postmenopausal was 0.82 (CI = 0.69-0.97); of high parity (three or more births compared with none) was 0.72 (CI = 0.61-0.86); of late age at first birth (over 30 years of age compared with 20 or under) was 1.46 (CI = 1.22-1.75); of benign breast disease was 1.53 (CI = 1.41-1.65); of maternal history of breast cancer was 1.38 (CI = 1.14-1.67); and history of a sister with breast cancer was 1.47 (CI = 1.27-1.70). Greater duration of schooling (more than high-school graduation compared with less than high-school graduation) was associated significantly with higher risk in age-adjusted analyses, but was attenuated after controlling for other risk factors. Total fat intake (adjusted for energy consumption) was not associated significantly with breast cancer risk in any strata of these non-dietary risk factors. We observed a marginally significant interaction between total fat intake and risk of breast cancer according to history of benign breast disease, with fat intake being associated nonsignificantly positively with risk among women with a previous history of benign breast disease; no other significant interactions were observed. Risks for reproductive factors were similar to those observed in case-control studies; relative risks for family history of breast cancer were lower. We found no clear evidence in any subgroups of a major relation between total energy-adjusted fat intake and breast cancer risk.
Bibliographical noteFunding Information:
Drs Hunter, Speizer, Willett, and Ms Yaun are with the Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA. Authors are also affiliated with the Harvard School of Public Health Department of Epidemiology, Boston, MA (Drs Hunter, Spiegelman, Willett), Department of Nutrition (Dr Willett), and Department of Biostatistics (Dr Spiegelman); NCIC Epidemiology Unit, Department of Preventive Medicine and Biostatistics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada (Drs Howe, Miller); Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, MN (Drs Folsom, Kushi); Department of Epidemiology, Maastricht University, The Netherlands (Dr van den Brandt); Department of Epidemiology, TNO Nutrition and Food Research Institute, Zeist, The Netherlands (Dr Goldbohm); Department of Social and Preventive Medicine, State University of New York at Buffalo, NY (Dr Graham); Arizona Cancer Center, University of Arizona, College of Medicine, Tucson, AZ (Dr Marshall); Department of Cancer Epidemiology, University Hospital, Uppsala, Sweden (Drs Adami, Wolk). Address correspondence to Dr Hunter, Channing Laboratory, 181 Longwood Ave, Boston, MA 02115, USA. This project is funded by research grants NIH CA55075 and CA50597 and by a Faculty Research Award (FRA-455) to Dr Hunter from the American Cancer Society.
- Breast cancer
- Reproductive factors