Vicky C Chang 1 2, Michelle Cotterchio 1 2, Susan J Bondy 1, Joanne Kotsopoulos 1 3
Iron has been suggested to contribute to breast cancer development through oxidative stress generation. This study investigated associations between iron intake and breast cancer risk, overall and by menopausal and estrogen receptor/progesterone receptor (ER/PR) status, and modification by oxidative stress-related genetic polymorphisms (MnSOD, GSTM1, and GSTT1). A population-based case-control study (3,030 cases and 3,402 controls) was conducted in Ontario, Canada. Iron intake (total, dietary, supplemental, heme, non-heme) was assessed using a validated food frequency questionnaire. Odds ratios (OR) and 95% confidence intervals (CI) were estimated from multivariable logistic regression models. Interactions between iron intake and genotypes were assessed among 1,696 cases and 1,761 controls providing DNA. Overall, no associations were observed between iron intake and breast cancer risk. Among premenopausal women, total, dietary, and dietary non-heme iron were positively associated with ER-/PR- breast cancer risk (all Ptrend < 0.05). Among postmenopausal women, supplemental iron was associated with reduced breast cancer risk (OR>18 vs. 0 mg/day = 0.68, 95% CI: 0.51-0.91), and dietary heme iron was associated with an increased risk, particularly the ER-/PR- subtype (ORhighest vs. lowest quintile = 1.69, 95% CI: 1.16-2.47; Ptrend = 0.02). Furthermore, GSTT1 and combined GSTM1/GSTT1 polymorphisms modified some of the associations. For example, higher dietary iron was most strongly associated with increased breast cancer risk among women with GSTT1 deletion or GSTM1/GSTT1 double deletions (Pinteraction < 0.05). Findings suggest that iron intake may have different effects on breast cancer risk according to menopausal and hormone receptor status, as well as genotypes affecting antioxidant capacity. This article is protected by copyright. All rights reserved.