Factors related to late menopause and early menarche as risk factors for breast cancer.

To investigate underlying factors of late menopause and early menarche which are regarded as risk factors for breast cancer, we analyzed the relationships between ages at menarche and menopause, and other environmental and physical factors using the data of a population-based survey conducted in Aichi Prefecture, Japan. The analysis on menopause was based on 3,148 women aged 55 or more and the analysis on menarche was based on 16,392 women aged 40 or more. These subjects were grouped into three groups (early, average and late groups) according to their ages at menopause and menarche. Women with late menopause had larger height, weight and body mass index and included more professional, administrative and office workers, more daily fish & shellfish consumers and more women with colorectal cancer history of the mother and less current smokers. Women with early menarche also had larger height, weight and body mass index and more residence in a metropolitan area and consumed more bread, meats, fish & shellfish, vegetables, fruits, milk and black tea and less rice, miso soup and pickles. In a multiple regression analysis, occupation, weight, daily or occasional drinking and daily intake of fish & shellfish were positively and smoking was inversely associated with late menopause, while residence in a metropolitan area, weight and daily intakes of bread, milk and green-yellow vegetables were positively associated with early menarche. These results suggest the importance of underlying factors of early menarche and late menopause in the etiology and prevention of breast cancer.