1 Département Cancer et Environnement, Centre Léon Bérard, Lyon, France
2 Université Claude Bernard Lyon 1, Villeurbanne, France
3 Inserm, Center for Research in Epidemiology and Population Health (CESP), U11018, Team "Lifestyle, genes and health", Villejuif, France
4 Université Paris-Sud, UMRS 1018, Villejuif, France
5 Gustave Roussy, Villejuif, France
6 Nutritional Epidemiology Group, Nutrition and Metabolism Section, International Agency for Research on Cancer, Lyon, France
Purpose: Dioxins are environmental and persistent pollutants mostly emitted from combustion facilities. Known to be endocrine disrupting chemicals, dioxins are suspected to increase breast cancer (BC) risk. Although diet is considered the primary source of dioxin exposure, no previous study has been published on dietary dioxin exposure in relation to BC risk. We aimed at assessing dietary dioxin exposure among women from the French E3N prospective cohort and estimating BC risk associated with this exposure.
Methods: The study included 63,830 women from the E3N cohort who completed a diet history questionnaire (DHQ) in 1993 and were followed until 2008. Dietary dioxin exposure was estimated by combining consumption data from the E3N DHQ and food dioxin contamination data from a French national monitoring program (CSHPF 2000). Hazard ratios (HR) and 95% confidence intervals (CI) were estimated by Cox models adjusted for BC risk factors.
Results: Mean dietary dioxin exposure was estimated at 1.3 ± 0.4 pg/kg body weight (BW)/day. A 0.4 pg/kg BW/day increase in dioxin intake was not associated with overall BC risk (HR=1.00; 95%CI: 0.96, 1.05). A significant decrease in risk of estrogen receptor negative (ER-)/progesterone receptor negative (PR-) tumors was observed among post-menopausal women in the upper quartile of estimated dioxin intake (HR for Q4 vs. Q1: 0.65; 95%CI: 0.45, 0.96; P for trend across quartiles=0.0463).
Conclusions: Overall, no association between estimated dietary dioxin exposure and BC risk was found among E3N women. Further studies should include both dietary and environmental exposures to determine whether low-dose dioxin exposure is associated with BC risk.
Funding sources: Lyon-UCBL, CLARA, ADEME. E3N: MGEN, LNCC, IGR and Inserm.