Soyfood Intake during Adolescence and Subsequent Risk Of Breast Cancer among Chinese Women

Author: Xian Ou Shu, Fan Jin, Qi Dai, Wanqing Wen, John Potter, Lawrence Kushi, Zhixian Ruan, Yu-Tang Gao and Wei Zheng
Publication: Cancer Epidemiology, Biomarkers and Prevention. 2001 May;10(5):483-8

The incidence of breast cancer is are two to three times lower among Chinese and other Asian women that for Caucasian women. Migration studies have suggested that genetic differences are not the main factor. Instead, many epidemiological studies have showed that soy consumption contribute to lower risk of breast cancer. Soy is rich in isoflavones (mainly genistein and daidzein) which seems to have anti-cancer properties. Soy isoflavones compete with endogenous estrogens in binding with estrogen receptors. Isoflavones have chemopreventive actions such as antivirus, antioxidant, antibacterial and immune enhancement. There are also many experimental studies, which suggested that soy have cancer inhibitory effects on breast cancer. The isoflavone genistein inhibits the proliferation of breast cancer cells, stimulated by estrogen and growth factor. The purpose of this study was to investigate epidemiological evidence of the association of soy consumption during adolescence and breast cancer.

During adolescence (13 to 15 years), the breast tissue of girls is developed and is most sensitive to environmental stimuli, including carcinogens. During adolescence, the mammary glands are developed. For this study (the Shanghai Breast Cancer Study), the dietary intake 1556 women who had breast cancer and 1556 controls were compared. The information has obtained by interviewing the women, and where possible interviewing the mothers. The soyfoods were divided in three groups: tofu, soy milk and other soy products. The total soyfood consumption was calculated by adding the soy protein of each soyfood.

Breast cancer cases reported a lower soy intake than the controls: women with breast cancer ate during adolescence on average 6.45 grams soy protein as compared to 7.23 of the controls. After the adjustment of other risk factors, the adolescence soy intake was inversely associated with breast cancer risk. This inverse relationship existed for all three types of soyfoods, which were examined (tofu, soymilk and other soy products) and was observed for both premenopausal and postmenopausal women. The inverse relationship between soy intake during adolescence and breast cancer risk was not influenced by adult soy intake.

The investigators concluded that the Shangai Breast Cancer Study adolescent soy intake was inversely associated with the risk of breast cancer in adult life. The findings may explain, at least partially the difference in breast cancer incidence among Asians and Caucasians. The investigators also suggested that it is important to initiate cancer prevention programs early in life.