Dietary fiber intake and risk of breast cancer defined by estrogen and progesterone receptor status: the Japan Public Health Center-based Prospective Study.
OBJECTIVE
Epidemiological studies have suggested a protective effect of dietary fiber intake on breast cancer risk while the results have been inconsistent. Our study aimed to investigate the association between dietary fiber intake and breast cancer risk and to explore whether this association is modified by reproductive factors and hormone receptor status of the tumor.


METHODS
A total of 44,444 women aged 45 to 74 years from the Japan Public Health Center-based Prospective Study were included in analyses. Dietary intake assessment was performed using a validated 138-item food frequency questionnaire (FFQ). Hazard ratios (HRs) and 95% confidence intervals (CIs) for breast cancer incidence were calculated by multivariate Cox proportional hazards regression models.


RESULTS
During 624,423 person-years of follow-up period, 681 breast cancer cases were identified. After adjusting for major confounders for breast cancer risk, inverse trends were observed but statistically non-significant. Extremely high intake of fiber was associated with decreased risk of breast cancer but this should be interpreted with caution due to limited statistical power. In stratified analyses by menopausal and hormone receptor status, null associations were observed except for ER-PR- status.


CONCLUSIONS
Our findings suggest that extreme high fiber intake may be associated with decreased risk of breast cancer but the level of dietary fiber intake among Japanese population might not be sufficient to examine the association between dietary fiber intake and breast cancer risk.
Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan.
Saki
S
Narita
AXA Department of Health and Human Security, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan. mnminoue@m.u-tokyo.ac.jp.|Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan. mnminoue@m.u-tokyo.ac.jp.
Manami
M
Inoue
AXA Department of Health and Human Security, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan.|Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Eiko
E
Saito
Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan.
Sarah K
SK
Abe
Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Norie
N
Sawada
Department of Nutrition Management, Sagami Women's University, 2-1-1 Bunkyo Minami Ward, Sagamihara, Kanagawa, 252-0307, Japan.
Junko
J
Ishihara
Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Motoki
M
Iwasaki
Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Taiki
T
Yamaji
Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Taichi
T
Shimazu
Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Shizuka
S
Sasazuki
Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 1130033, Japan.
Kenji
K
Shibuya
Epidemiology and Prevention Group, Center for Public Health Sciences, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan. stsugane@ncc.go.jp.
Shoichiro
S
Tsugane
D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology / Q000235:genetics / Q000378:metabolism; D004043:Dietary Fiber; D004967:Estrogens; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan; D008875:Middle Aged; D011446:Prospective Studies; D011634:Public Health; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism*; D012306:Risk
D004043:Dietary Fiber; D004967:Estrogens; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone
Breast cancer; Dietary fiber intake; Estrogen receptor (ER); Progesterone receptor (PR)