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Original Investigation
November 2015

Mediterranean Diet and Invasive Breast Cancer Risk Among Women at High Cardiovascular Risk in the PREDIMED Trial: A Randomized Clinical Trial

Author Affiliations
  • 1Department of Preventive Medicine and Public Health, University of Navarra–School of Medicine, Pamplona, Navarra, Spain
  • 2Centro de Investigación Biomédica en Red Fisiopatología de la Obesidad y Nutrición, Instituto de Salud Carlos III, Madrid, Spain
  • 3Human Nutrition Unit, Faculty of Medicine and Health Sciences, Biochemistry Biotechnology Department, Universitat Rovira i Virgili, Reus, Spain
  • 4Servicio Navarro de Salud-Osasunbidea, Pamplona, Navarra, Spain
  • 5IdiSNA, Navarra Institute for Health Research, Pamplona, Navarra, Spain
  • 6Department of Internal Medicine, Institut d’Investigacions Biomèdiques August Pi I Sunyer, Hospital Clinic, University of Barcelona, Barcelona, Spain
  • 7Lipid Clinic, Department of Endocrinology and Nutrition, Institut d’Investigacions Biomèdiques August Pi I Sunyer, Hospital Clinic, University of Barcelona, Barcelona, Spain
  • 8Department of Preventive Medicine, University of Valencia, Valencia, Spain
  • 9Cardiovascular and Nutrition Research Group, Institut de Recerca Hospital del Mar, Barcelona, Spain
  • 10Departments of Nutrition and Epidemiology, Harvard School of Public Health, Boston, Massachusetts
  • 11Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
  • 12University Hospital of Alava, Vitoria, Basque Country, Spain
  • 13Department of Preventive Medicine, University of Malaga, Malaga, Spain
  • 14Instituto de Investigación Sanitaria de Palma (IdISPa), Hospital Universitario Son Espases, Palma de Mallorca, Spain
  • 15Department of Family Medicine, Primary Care Division of Sevilla, Sevilla, Spain
  • 16Research Institute of Biomedical and Health Sciences, University of Las Palmas de Gran Canaria, Las Palmas, Spain
  • 17Lipids and Vascular Risk Unit, Internal Medicine, Hospital Universitario de Bellvitge-IDIBELL-UB, Hospitalet de Llobregat, Barcelona, Spain
  • 18Primary Care Division of Barcelona, Institut Català de la Salut and IDiap-Jordi Gol, Barcelona, Spain
  • 19Centro de Investigación Biomédica en Red Epidemiología y Salud Pública, Instituto de Salud Carlos III, Madrid, Spain
JAMA Intern Med. 2015;175(11):1752-1760. doi:10.1001/jamainternmed.2015.4838
Abstract

Importance  Breast cancer is the leading cause of female cancer burden, and its incidence has increased by more than 20% worldwide since 2008. Some observational studies have suggested that the Mediterranean diet may reduce the risk of breast cancer.

Objective  To evaluate the effect of 2 interventions with Mediterranean diet vs the advice to follow a low-fat diet (control) on breast cancer incidence.

Design, Setting, and Participants  The PREDIMED study is a 1:1:1 randomized, single-blind, controlled field trial conducted at primary health care centers in Spain. From 2003 to 2009, 4282 women aged 60 to 80 years and at high cardiovascular disease risk were recruited after invitation by their primary care physicians.

Interventions  Participants were randomly allocated to a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (advice to reduce dietary fat).

Main Outcomes and Measures  Breast cancer incidence was a prespecified secondary outcome of the trial for women without a prior history of breast cancer (n = 4152).

Results  After a median follow-up of 4.8 years, we identified 35 confirmed incident cases of breast cancer. Observed rates (per 1000 person-years) were 1.1 for the Mediterranean diet with extra-virgin olive oil group, 1.8 for the Mediterranean diet with nuts group, and 2.9 for the control group. The multivariable-adjusted hazard ratios vs the control group were 0.31 (95% CI, 0.13-0.77) for the Mediterranean diet with extra-virgin olive oil group and 0.53 (95% CI, 0.23-1.26) for the Mediterranean diet with nuts group. In analyses with yearly cumulative updated dietary exposures, the hazard ratio for each additional 5% of calories from extra-virgin olive oil was 0.72 (95% CI, 0.57-0.90).

Conclusions and Relevance  This is the first randomized trial finding an effect of a long-term dietary intervention on breast cancer incidence. Our results suggest a beneficial effect of a Mediterranean diet supplemented with extra-virgin olive oil in the primary prevention of breast cancer. These results come from a secondary analysis of a previous trial and are based on few incident cases and, therefore, need to be confirmed in longer-term and larger studies.

Trial Registration  ISRCTN.org Identifier: ISRCTN35739639

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