Life-style in Relation to the Risk of Breast Cancer*

Abstract

A hospital-based case-control analysis was conducted to assess the relationship of life-style to breast cancer in Japan. The study population was selected among the outpatients of a hospital where information on life-style had been routinely collected prior to diagnosis since 1987. The ageadjusted risk to breast cancer significantly decreased with marital status, fullterm pregnancy history, number of fullterm pregnancies, number of breastfed children, and the average length of breastfeeding, while age at first fullterm pregnancy and family history of breast cancer were positively associated with the risk. The adjusted risk, controlling for potential confoundings, significantly decreased in alcohol drinkers. On the other hand, there was a significant dose-response gradient of increasing risk with smoking. No relationship of physical activity to the disease was observed. There were significant decreases in the risk with increasing intake of rice, bean curd, soy bean paste, and green vegetables. However, no evidence of increase in the risk was found with a high fat diet. These findings suggest that further study under the specific hypothesis in a different population should be followed to confirm the different risk factors of breast cancer in Oriental people from those in the Western countries.