Dietary intakes of x-6 and x-3 polyunsaturated fatty acids and the risk of breast cancer Anne C.M. Thi ebaut 1 ,V eronique Chaje `s 2 , Mariette Gerber 3 , Marie-Christine Boutron-Ruault 1 , Virginie Joulin 2 , Gilbert Lenoir 2 , Franco Berrino 4 , Elio Riboli 5 , Jacques B enichou 6 and Franc ¸oise Clavel-Chapelon 1 * 1 INSERM, ERI-20, Institut Gustave Roussy, Villejuif Cedex, France 2 CNRS-FRE 2939, Institut Gustave Roussy, Villejuif Cedex, France 3 Centre de Recherche en Canc erologie, INSERM-CRLC, Montpellier, France 4 Istituto Nazionale per la Cura e lo Studio dei Tumori, Unita` Operativa di Epidemiologia, Milan, Italy 5 Imperial College, Department of Epidemiology & Public Health, London, United Kingdom 6 INSERM, U657, CHU et Facult  e de M edecine-Pharmacie de Rouen, Unit  e de Biostatistique, Rouen, France Experimental studies suggest detrimental effects of x-6 polyunsa- turated fatty acids (PUFA), and beneficial effects of x-3 PUFAs on mammary carcinogenesis, possibly in interaction with antioxi- dants. However, PUFA food sources are diverse in human diets and few epidemiologic studies have examined whether associations between dietary PUFAs and breast cancer risk vary according to food sources or antioxidant intakes. The relationship between individual PUFA intakes estimated from diet history question- naires and breast cancer risk was examined among 56,007 French women. During 8 years of follow-up, 1,650 women developed inva- sive breast cancer. Breast cancer risk was not related to any die- tary PUFA overall; however, opposite associations were seen according to food sources, suggesting other potential effects than PUFA per se. Breast cancer risk was inversely associated with a- linolenic acid (ALA) intake from fruit and vegetables [highest vs. lowest quintile, hazard ratio (HR) 0.74; 95% confidence interval (CI) 0.63, 0.88; p trend < 0.0001], and from vegetable oils (HR 0.83; 95% CI 0.71, 0.97; p trend 0.017). Conversely, breast cancer risk was positively related to ALA intake from nut mixes (p trend 0.004) and processed foods (p trend 0.068), as was total ALA intake among women in the highest quintile of dietary vitamin E (p trend 0.036). A significant interaction was also found between x-6 and long-chain x-3 PUFAs, with breast cancer risk inversely related to long-chain x-3 PUFAs in women belonging to the high- est quintile of x-6 PUFAs (p interaction 0.042). These results emphasize the need to consider food sources, as well as interac- tions between fatty acids and with antioxidants, when evaluating associations between PUFA intakes and breast cancer risk. ' 2008 Wiley-Liss, Inc. Key words: fatty acids; vitamin E; breast cancer; prospective studies; prevention Breast cancer is the most frequent malignancy among women in Western Europe, North America 1 and more recently in Japan. 2 In France, about 50,000 incident cases were observed and 11,200 deaths (19% of cancer mortality) were due to breast cancer in 2005. 3 It has been estimated that as many as half of breast cancer deaths could be avoided through dietary modifications, 4 although the available evidence is far from convincing for most dietary fac- tors. 5 The role of fat intake in breast cancer etiology has been investigated for long 6 but still remains controversial. 7 A meta- analysis of epidemiologic studies 8 observed a significant increase in breast cancer risk with high saturated fat intake but no associa- tion with monounsaturated and polyunsaturated fatty acid (PUFA) intakes. A recent prospective study 9 reported varying associations of breast cancer with dietary fat depending on its food sources, hence suggesting a possible explanation for the discrepant results across epidemiologic studies. Moreover, in a meta-analysis cover- ing 97 studies in rodents, Fay et al. 10 underlined the need to distin- guish between the effects of x-6 and x-3 PUFAs, with x-6 PUFAs showing strong tumor-enhancing effects and x-3 PUFAs nonsigni- ficant protective effects. Additional experimental studies suggest that high intakes of x-3 PUFAs could exert inhibitory effects on mammary tumorigenesis through competition with x-6 PUFAs 11 or formation of oxidation products 12 that may in turn depend on the antioxidant status. 13–15 So far, such interactions have hardly been examined in epidemiologic studies. We analyzed the relationship of breast cancer risk to PUFA intake, overall and by food sources, in a large prospective cohort of French women with a high diversity of dietary habits across the national territory. 16 The analysis focused on dietary x-3 PUFA intakes which have been hypothesized to encompass a potential for preventive strategies. Nowadays, a number of dietary fish oil supplements and foods enriched with x-3 PUFAs are available on the market, although their benefit on cancer prevention has not yet been ascertained. 17 As a secondary analysis, we investigated potential interactions of x-3 PUFA intakes with intakes of x-6 PUFAs and vitamin E, a liposoluble antioxidant, in relation to breast cancer risk. Material and methods Study population E3N is a prospective cohort study on cancer risk factors con- ducted in France among women insured with the ‘‘Mutuelle G en erale de l’Education Nationale’’ (MGEN), a national health in- surance scheme covering teachers, teacher spouses and employees of the National Education System. 18 Overall, 98,995 women vol- unteers aged 40-65 years were enrolled in 1989-1991 after reply- ing to a baseline questionnaire and giving their informed consent. The study was approved by the French National Commission for Data Protection and Privacy. In 1993, a diet history questionnaire 19 was sent to participants who had previously answered both the baseline questionnaire and a second questionnaire on reproductive history and hormonal treatments (n 5 95,644). After two reminders for nonrespondents, 77,613 dietary questionnaires were collected between June 1993 Abbreviations: ALA, a-linolenic acid; BMI, body mass index; CI, confi- dence interval; E3N, Etude Epid emiologique aupre `s de femmes de la Mutuelle G en erale de l’Education Nationale; EPA, eicosapentaenoic acid; EPIC, European Prospective Investigation into Cancer and Nutrition; DHA, docosahexaenoic acid; DPA, docosapentaenoic acid; HR, hazard ra- tio; INSERM, Institut National de la Sant e et de la Recherche M edicale; MGEN, Mutuelle G en erale de l’Education Nationale; PUFA, polyunsatu- rated fatty acids. Grant sponsors: Foundation de France, French League Against Cancer, Carrefour Foundation, French Ministry of Research, French League Against Cancer, the European Community, 3M Company, ‘‘Mutuelle G en erale de l’Education Nationale’’, the French Institute of Health and Medical Research, Gustave Roussy Institute and several General Councils in France. Present address of Anne C.M. Thi ebaut: INSERM, U657, Institut Pas- teur, Paris, France. *Correspondence to: INSERM, ERI-20, Institut Gustave Roussy, Espace Maurice Tubiana, 39 rue Camille Desmoulins, 94805 Villejuif Cedex, France. Fax: 133 (0)1 42 11 40 00. E-mail: clavel@igr.fr Received 6 May 2008; Accepted after revision 29 July 2008 DOI 10.1002/ijc.23980 Published online 9 September 2008 in Wiley InterScience (www.interscience. wiley.com). Int. J. Cancer: 124, 924–931 (2009) ' 2008 Wiley-Liss, Inc. Publication of the International Union Against Cancer