We assessed associations between blood levels of estrogen and androgen and breast cancer risk factors in premenopausal Japanese women. A total of 551 premenopausal women who reported having regular menstrual cycles less than 40 days long were included in the present study. Women were not included if they were using oral contraceptives or hormone therapy, or if they had cancer, diabetes mellitus, chronic hepatitis, or thyroid disease. Information on potential breast cancer risk factors including body size, physical activity, and reproductive factors were obtained using a self‐administered questionnaire. The phase of menstrual cycle at blood donation, categorized in early follicular, late follicular, peri‐ovulatory, midluteal, or other luteal, was used for adjustment together with age. Estradiol level was significantly inversely associated with body mass index (BMI), while testosterone and DHEAS levels were significantly positively associated with BMI; the geometric mean of estradiol in women with BMI at or above 24 kg/m2 was about 25% lower than that in women with BMI below 18 kg/m2. The geometric means of testosterone and DHEAS were 31% and 24% higher, respectively, in women in the high BMI group. Nulliparous women had significantly higher testosterone levels than parous women. Breastfeeding was associated with decreased levels of testosterone and DHEAS. Physical activity, age at menarche, number of births, and age at first birth were not significantly associated with these hormone levels. A reduced breast cancer risk of obese premenopausal women may be due, in part, to a decreased estradiol level.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):B117.

Copyright © January 7, 2010, American Association for Cancer Research
2010