title: Dietary isoflavone intake and breast cancer risk in case-control studies in Japanese, Japanese Brazilians, and non-Japanese Brazilians.
abstract: Although epidemiologic studies have shown an inverse association between isoflavones and breast cancer risk, little evidence for a dose-response relation is available. We conducted hospital-based case-control studies of patients aged 20-74 years with primary, incident, histologically confirmed invasive breast cancer, and matched controls from medical checkup examinees in Nagano, Japan and from cancer-free patients in São Paulo, Brazil. A total of 850 pairs (390 Japanese, 81 Japanese Brazilians and 379 non-Japanese Brazilians) completed validated food frequency questionnaires. The odds ratio of breast cancer according to isoflavone intake was estimated using a conditional logistic regression model. We found a statistically significant inverse association between isoflavone intake and the risk of breast cancer for Japanese Brazilians and non-Japanese Brazilians. For Japanese, a non-significant inverse association was limited to postmenopausal women. In the three populations combined, breast cancer risk linearly decreased from 'no' to 'moderate' isoflavone intake and thereafter leveled off. Compared to non-consumers, adjusted odds ratios (95% confidence interval) for consumers in increasing quintile intake categories (median intake in each category: 8.7, 23.1, 33.8, 45.7, and 71.3 mg/day) were 0.69 (0.44-1.09), 0.54 (0.31-0.94), 0.45 (0.26-0.77), 0.34 (0.19-0.62), and 0.43 (0.24-0.76), respectively. Overall, we found an inverse association between dietary isoflavone intake and risk of breast cancer. Our finding suggests a risk-reducing rather than risk-enhancing effect of isoflavones on breast cancer within the range achievable from dietary intake alone. In addition, women may benefit from risk reduction if they consume at least moderate amounts of isoflavones.
authors.affiliation: Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan. moiwasak@ncc.go.jp
authors.forename: Motoki
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Gerson Shigeaki
authors.initials: GS
authors.lastname: Hamada
authors.forename: Ines Nobuko
authors.initials: IN
authors.lastname: Nishimoto
authors.forename: Mario Mourão
authors.initials: MM
authors.lastname: Netto
authors.forename: Juvenal
authors.initials: J
authors.lastname: Motola
authors.forename: Fábio Martins
authors.initials: FM
authors.lastname: Laginha
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kasuga
authors.forename: Shiro
authors.initials: S
authors.lastname: Yokoyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Onuma
authors.forename: Hideki
authors.initials: H
authors.lastname: Nishimura
authors.forename: Ritsu
authors.initials: R
authors.lastname: Kusama
authors.forename: Minatsu
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Junko
authors.initials: J
authors.lastname: Ishihara
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Yamamoto
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Hanaoka
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsugane
mesh_terms: D000328:Adult; D000368:Aged; D044466:Asian People; D001938:Brazil / Q000453:epidemiology; D001943:Breast Neoplasms / Q000453:epidemiology*; D016022:Case-Control Studies; D004032:Diet; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage*; D007564:Japan / Q000453:epidemiology; D008875:Middle Aged; D017698:Postmenopause; D012307:Risk Factors
chemical_list: D007529:Isoflavones