Environment and Breast Cancer: Science Review

Evidence From Humans
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Soy, isoflavones, and breast cancer risk in Japan
Yamamoto, S., Sobue, T., Kobayashi, M., Sasaki, S., Tsugane, S. J Natl Cancer Inst. 2003. 95:12, 906-13.
Study design
Prospective cohort
Funding agency
Other: Ministry of Health, Labour and Welfare of J
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Post menopausal
Pre menopausal
Number in Cohort
Cohort: 21,852
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
In: Women participating in the Japan Public Health Center-Based Prospective Study on Cancer and Cardiovascular Diseases, aged 40-59 years who registered their address in one of the 14 administrative districts supervised by five public health centers. Ex: One public health center because incidence data were not collected, women diagnosed with breast cancer before study entry, women who did not answer the baseline questionnaire, who answered a positive history of any cancer, or with missing information in the food questionnaire
Exposure Investigated
Exposures investigated
Soy and isoflavone
How exposure was measured
Questionnaire, self-administered, FFQ
Exposure assessment comment
38 foods items, only 2 for soy foods, did not consider isoflavone from other food sources, lowerst quartile of isoflavone consumption is high compared to studies in Western countries.
Statistical Analysis
Ethnic groups with separate analysis
If this study provided a separate analysis by ethnic or racial group, the groups are listed here.
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Not considered: BMI
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Description of major analysis
Adjusted RR with 95% CI, higher versus lower quartile of intake, stratified by menopausal status, latency period 3 years. Follow-up 10 years
Strength of associations reported
Miso soup: 0.6 (0.34-1.1); Soy: 0.81 (0.49-1.3); Isoflavone: 0.46 (0.25-0.84);
Isoflavone: Premenopausal: 0.66 (0.25-1.7), Postmenopausal: 0.32 (0.14-0.71)
Results Comments
Statistically significant inverse association between isoflavone intake and risk of breast cancer in Japanese women. When stratified by menopausal status, the inverse association was stronger in post-menopausal women for isoflavone consumption
Author address
Cancer Information and Epidemiology Division, National Cancer Center Research Institute, Tokyo, Japan. siyamamo@ncc.go.jp
Reviewers Comments
Menopausal status was only assess at baseline not at breast cancer diagnosis.