Soya foods and breast cancer risk: a prospective study in Hiroshima and Nagasaki, Japan

The association between soya foods and breast cancer risk was investigated in a prospective study of 34 759 women in Hiroshima and Nagasaki, Japan. Wo men completed dietary questionnaires in 1969-1970 and/or in 1979-1981 and w ere followed for incident breast cancer until 1993. The analysis involved 4 27 cases of primary breast cancer in 488 989 person-years of observation. T he risk for breast cancer was not significantly associated with consumption of soya foods, for tofu, relative risks adjusted for attained age, calenda r period, city, age at time of bombings and radiation dose to the breast we re 0.99 (95% CI 0.80-1.24) for consumption two to four times per week and 1 .07 (0.78-1.47) for consumption five or more times per week, relative to co nsumption once a week or less; for mise soup, relative risks were 1.03 (0.8 1-1.31) for consumption two to four times per week and 0.87 (0.68-1.12) for consumption five or more times per week, relative to consumption once a we ek or less. These results were not materially altered by further adjustment s for reproductive variables and were similar in women diagnosed before age 50 and at ages 50 and above, Among 17 other foods and drinks examined only dried fish (decrease in relative risk with increasing consumption) and pic kled vegetables (higher relative risk with higher consumption) were signifi cantly related to breast cancer risk; these associations were not prior hyp otheses and, because of the large number of comparisons made, they may be d ue to chance. (C) 1999 Cancer Research Campaign.