Kossman DA, Williams NI, Domchek SM, Kurzer MS, Stopfer JE, Schmitz KH. Exercise lowers estrogen and progesterone levels in premenopausal women at high risk of breast cancer. J Appl Physiol 111: 1687-1693, 2011. First published September 8, 2011 doi:10.1152/japplphysiol.00319.2011.-Experimental and clinical data support a role for estrogens in the development and growth of breast cancer, and lowered estrogen exposure reduces breast cancer recurrence and new diagnoses in high-risk women. There is varied evidence that increased physical activity is associated with breast cancer risk reduction in both pre-and postmenopausal women, perhaps via lowered estrogen levels. The purpose of this study was to assess whether exercise intervention in premenopausal women at increased breast cancer risk reduces estrogen or progesterone levels. Seven healthy premenopausal women at high risk for breast cancer completed a seven-menstrual-cycle study. The study began with two preintervention cycles of baseline measurement of hormone levels via daily first-morning urine collection, allowing calculation of average area under the curve (AUC) hormone exposure across the menstrual cycle. Participants then began five cycles of exercise training to a maintenance level of 300 min per week at 80 -85% of maximal aerobic capacity. During the last two exercise cycles, urinary estradiol and progesterone levels were again measured daily. Total estrogen exposure declined by 18.9% and total progesterone exposure by 23.7%. The declines were mostly due to decreased luteal phase levels, although menstrual cycle and luteal phase lengths were unchanged. The study demonstrated the feasibility of daily urine samples and AUC measurement to assess hormone exposure in experimental studies of the impact of interventions on ovarian hormones. The results suggest value in exercise interventions to reduce hormone levels in high-risk women with few side effects and the potential for incremental benefits to surgical or pharmacologic interventions. menstrual cycle; BRCA1/2 mutation carriers EXPERIMENTAL AND CLINICAL data support a role for estrogens in the development and growth of breast cancer, with the primary hypothesis being that estrogens interact with receptors in a manner that increases cell proliferation rates (7, 70). Lowering endogenous estrogen levels via bilateral oopherectomy or blocking estrogen effects with selective estrogen receptor modulators such as tamoxifen and raloxifene reduce the rate of initial diagnoses among women at high risk of developing breast cancer (11,29,38,34,36,55). Early onset of menarche, late first full-term pregnancy, and late menopause, factors that increase lifetime estrogen exposure, have all been associated with higher rates of breast cancer. On the other hand, there is conflicting epidemiologic evidence of a link between premenopausal endogenous estrogens and breast cancer risk. Of seven studies identified, four observed a significant inverse association of endogenous estrogens with breast cancer risk in premenopausal w...