Soyfood intake during adolescence and subsequent risk of breast cancer among Chinese women

Many experimental but few epidemiological studies have suggested that soyfo ods and their constituents have cancer-inhibitory effects on breast cancer. No epidemiological study has evaluated the association of adolescent soyfo od intake with the risk of breast cancer. To evaluate the effect of soyfood intake during adolescence, one of the periods that breast tissue is most s ensitive to environmental stimuli, on subsequent risk of breast cancer, we analyzed data from a population-based case control of 1459 breast cancer ca ses and 1556 age-matched controls (respective response rates were 91.1% and 90.3%). Information on dietary intake from ages 13-15 years was obtained b y interview from all study participants and, in addition, from mothers of s ubjects less than 45 years of age (296 cases and 359 controls). Odds ratios (ORs) and 95% confidence intervals (Cls) derived from unconditional logist ic models were used to measure soyfood intake and breast cancer risk. After adjustment for a variety of other risk factors, adolescent soyfood intake was inversely associated with risk, with ORs of 1.0 (reference), 0.75 (95% CI, 0.60-0.93), 0.69 (95% CI, 0.55-0.87), 0.69 (95% CI, 0.55-0.86), and 0.5 1 (95% CI, 0.40-0.65), respectively, for the lowest to highest quintiles of total soyfood intake (trend test, P < 0.001). The inverse association was observed for each of the soyfoods examined and existed for both pre- and po stmenopausal women. Adolescent soyfood intakes reported by participants' mo thers were also inversely associated with breast cancer risk (P for trend < 0.001), with an OR of 0.35 (95% CI, 0.21-0.60) for women in the highest so yfood intake group. Adjustment for rice and wheat products, the major energ y source in the study population, and usual adult soyfood intake did not ch ange the soyfood associations. Our study suggests that high soy intake duri ng adolescence may reduce the risk of breast cancer in later life.