A new study has reported that levels of circulating hormones in postmenopausal women correspond to known breast cancer risk factors such as drinking alcohol, smoking and being overweight. Breast cancer risk has been reported to be positively associated with circulating concentrations of estrogens and androgens among postmenopausal women, but the factors determining of levels of these hormones are not well understood. To conduct the study, the authors performed analyses of breast cancer risk factors and circulating hormone concentrations in over 6,000 postmenopausal cancer-free controls in 13 previous prospective studies.

Concentrations of all hormones were found to be lower in older than younger women, with the largest difference for dehydroepiandrosterone sulphate (DHEAS), an androgen produced by the adrenal gland and which has been associated with higher risk of breast cancer. On the other hand, sex hormone binding globulin (SHBG), a glycoprotein that binds to testosterone and estradiol, thereby reducing breast cancer risk, was higher in the older women. Androgens were found to be lower overall in women with both ovaries removed than in naturally postmenopausal women, with the greatest difference for free testosterone.

All hormones were higher in obese compared to normal weight women, with the largest difference for free estradiol, whereas SHBG was lower in obese women. Smokers of at least 15 cigarettes per day were found to have higher levels of all hormones than non-smokers, with the greatest difference for testosterone. Drinkers of at least 20 g (0.7 oz.) alcohol per day also had higher levels of all hormones, but lower SHBG, than non-drinkers, with the greatest difference for DHEAS. Circulating hormone levels were not found to be strongly related to age at first period, number of children, age at first full-term pregnancy or family history of breast cancer. The study adds to evidence that "women can reduce their risk of developing breast cancer by maintaining a healthy weight, limiting their alcohol consumption and partaking in regular physical activity, according to Dr. Susie Jennings, Senior Policy Officer at Breakthrough Breast Cancer.