1. ¹Department of Epidemiology, German Institute of Human Nutrition Potsdam-Rehbrücke, Arthur-Scheunert-Allee 114-116, Nuthetal 14558, Germany
2. ²Institute of Cancer Epidemiology, Danish Cancer Society, Copenhagen, Denmark
3. ³Department of Clinical Epidemiology, Aalborg Hospital and Aarhus University Hospital, Aalborg, Denmark
4. ⁴Cancer Research UK, Epidemiology Unit, University Oxford, Oxford, UK
5. ⁵Department of Public Health and Primary Care, School of Clinical Medicine, University of Cambridge, Cambridge, UK
6. ⁶MRC Dunn Human Nutrition Unit, Cambridge, UK
7. ⁷Department of Medicine, Lund University, Malmö University Hospital, Malmö, Sweden
8. ⁸Epidemiology Unit, National Cancer Institute, Milan, Italy
9. ⁹Department of Hygiene and Epidemiology, School of Medicine, University of Athens, Athens, Greece
10. ¹⁰Department of Epidemiology, Havard School of Public Health, Boston, MA, USA
11. ¹¹International Agency for Research on Cancer (IARC-WHO), Lyon, France

Correspondence: Dr PH Lahmann, E-mail: Lahmann@mail.dife.de

Received 31 May 2005; Revised 19 July 2005; Accepted 28 July 2005; Published online 30 August 2005.

Abstract

We examined prospectively the association between weight change during adulthood and breast cancer risk, using data on 1358 incident cases that developed during 5.8 years of follow-up among 40 429 premenopausal and 57 923 postmenopausal women from six European countries, taking part in the European prospective investigation into cancer and nutrition study. Multivariate Cox regression models were used to calculate hazard ratios according to weight change (kg), defined as the weight difference between age at enrolment and age 20 adjusted for other risk factors. Changes in weight were not associated with premenopausal breast cancer risk. In postmenopausal women, weight gain was positively associated with breast cancer risk only among noncurrent hormone replacement therapy (HRT) users (P-trend 0.0002). Compared to women with a stable weight (2 kg), the relative risk for women who gained 15–20 kg was 1.50 (95% confidence interval (CI) 1.06–2.13). The pooled RR per weight gain increment of 5 kg was 1.08 (95% CI 1.04–1.12). Weight gain was not associated with breast cancer risk in current HRT users, although, overall, these women experienced a much higher risk of breast cancer compared with nonusers. Our findings suggest that large adult weight gain was a significant predictor of breast cancer in postmenopausal women not taking exogenous hormones.