Independent protective effect of lactation against breast cancer: a case-control study in Japan.
A case-control study was carried out to assess the risk of breast cancer associated with breast feeding in Japan. The data were obtained in a hospital-based case-control study of 521 women with breast cancer and 521 controls from January 1988 to December 1989. Statistical adjustment for potential confounders as well as a likelihood ratio test for linear trend was done by unconditional logistic regression. Compared with parous women who had never breast-fed, women with a positive history of breast feeding had an odds ratio of breast cancer of 0.62 (95% confidence interval 0.37-1.04). The trend of decreasing risk with increasing average months of breast feeding was statistically significant (chi 2 trend = 4.5, p less than 0.05), while it was was nonsignificant for the number of breast-fed children borne. Among premenopausal women, a significant linear relation with a log-transformed term of average months of breast feeding was noted, regardless of the age of the woman at first full-term pregnancy and parity (chi 2 trend = 5.3, p less than 0.05). The risk was the lowest among premenopausal women who had ever lactated for 7-9 months (adjusted odds ratio = 0.39, 95% confidence interval 0.15-0.97). These findings suggest that lactation has an independent protective effect against breast cancer in Japanese women.
Yoo
K Y
KY
Department of Preventive Medicine, Seoul National University College of Medicine, Korea.
Tajima
K
K
Kuroishi
T
T
Hirose
K
K
Yoshida
M
M
Miura
S
S
Murai
H
H
D000328:Adult; D000368:Aged; D044466:Asian People; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000208:ethnology / Q000517:prevention & control; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D007774:Lactation; D016015:Logistic Models; D008593:Menopause; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors