Exercise lowers estrogen and progesterone levels in premenopausal women at high risk of breast cancer

Abstract

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.

Fig. 1.

Hypothetical graph comparing higher (solid line) vs. lower (dashed line) total hormone exposure across a menstrual cycle as measured by the area under each curve.

Fig. 2.

Flow diagram of study protocol. First morning urine was collected every day for the first 2 menstrual cycles (Pre Cycles) before initiation of the exercise intervention. At the beginning of menstrual cycle 3, the exercise intervention started and continued through the end of menstrual cycle 7. First morning urine was again collected every day for menstrual cycles 6 and 7 (Post Cycles; cycles 4 and 5 of the exercise intervention).

Fig. 3.

Prescribed exercise with a build in both duration (minutes/week) and intensity [percent of heart rate (HR) maximum] of exercise to a maintenance level after week 12 of 300 minutes per week at between 80 and 85% of maximum target heart rate. MET, metabolic equivalent.