title: Dietary isoflavone intake is not statistically significantly associated with breast cancer risk in the Multiethnic Cohort.
abstract: Given the high intake levels of soya and low incidence rates of breast cancer in Asian countries, isoflavones, substances with an oestrogen-like structure occurring principally in soyabeans, are postulated to be cancer protective. In the present study, we examined the association of dietary isoflavone intake with breast cancer risk in 84,450 women (896 in situ and 3873 invasive cases) who were part of the Multiethnic Cohort (Japanese Americans, whites, Latinos, African Americans and Native Hawaiians) with a wide range of soya intake levels. The absolute levels of dietary isoflavone intake estimated from a baseline FFQ were categorised into quartiles, with the highest quartile being further subdivided to assess high dietary intake. The respective intake values for the quartiles (Q1, Q2, Q3, and lower and upper Q4) were 0-< 3·2, 3·2-< 6·7, 6·7-< 12·9, 12·9-< 20·3, and 20·3-178·7 mg/d. After a mean follow-up period of 13 years, hazard ratios (HR) and 95% CI were calculated using Cox regression models stratified by age and adjusted for known confounders. Linear trends were tested by modelling continuous variables of interest assigned the median value within the corresponding quartile. No statistically significant association was observed between dietary isoflavone intake and overall breast cancer risk (HR for upper Q4 v. Q1: 0·96 (95% CI 0·85, 1·08); P trend = 0·40). While the test for interaction was not significant (P=0·14), stratified analyses suggested possible ethnic/racial differences in risk estimates, indicating that higher isoflavone intakes may be protective in Latina, African American and Japanese American women. These results are in agreement with those of previous meta-analyses showing no protection of isoflavones at low intake levels, but suggesting inverse associations in populations consuming high amounts of soya.
authors.affiliation: University of Hawaii Cancer Center,701 Ilalo Street,Honolulu,HI96813,USA.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Morimoto
authors.affiliation: University of Hawaii Cancer Center,701 Ilalo Street,Honolulu,HI96813,USA.
authors.forename: Gertraud
authors.initials: G
authors.lastname: Maskarinec
authors.affiliation: University of Hawaii Cancer Center,701 Ilalo Street,Honolulu,HI96813,USA.
authors.forename: Song-Yi
authors.initials: SY
authors.lastname: Park
authors.affiliation: College of Tropical Agriculture and Human Resources, University of Hawaii,Honolulu,HI,USA.
authors.forename: Reynolette
authors.initials: R
authors.lastname: Ettienne
authors.affiliation: Purdue Pharma, L.P.,Stamford,CT,USA.
authors.forename: Rayna K
authors.initials: RK
authors.lastname: Matsuno
authors.affiliation: Department of Public Health Sciences,University of Hawaii,Honolulu,HI,USA.
authors.forename: Camonia
authors.initials: C
authors.lastname: Long
authors.affiliation: College of Nursing, University of Illinois at Chicago,Chicago,IL,USA.
authors.forename: Alana D
authors.initials: AD
authors.lastname: Steffen
authors.affiliation: Keck School of Medicine, University of Southern California,Los Angeles,CA,USA.
authors.forename: Brian E
authors.initials: BE
authors.lastname: Henderson
authors.affiliation: University of Hawaii Cancer Center,701 Ilalo Street,Honolulu,HI96813,USA.
authors.forename: Laurence N
authors.initials: LN
authors.lastname: Kolonel
authors.affiliation: University of Hawaii Cancer Center,701 Ilalo Street,Honolulu,HI96813,USA.
authors.forename: Loïc
authors.initials: L
authors.lastname: Le Marchand
authors.affiliation: University of Hawaii Cancer Center,701 Ilalo Street,Honolulu,HI96813,USA.
authors.forename: Lynne R
authors.initials: LR
authors.lastname: Wilkens
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology / Q000208:ethnology / Q000473:pathology / Q000517:prevention & control*; D002140:California / Q000453:epidemiology; D002278:Carcinoma in Situ / Q000453:epidemiology / Q000208:ethnology / Q000473:pathology / Q000517:prevention & control; D015331:Cohort Studies; D004032:Diet / Q000009:adverse effects / Q000208:ethnology; D005260:Female; D005500:Follow-Up Studies; D006254:Hawaii / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D007529:Isoflavones / Q000008:administration & dosage / Q000627:therapeutic use*; D016014:Linear Models; D008498:Medical Record Linkage; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D016016:Proportional Hazards Models; D012306:Risk; D018426:SEER Program; D045730:Soy Foods / Q000032:analysis
chemical_list: D007529:Isoflavones