Both elevated blood estrogen levels and an inactive lifestyle have been associated with an increased risk of breast cancer
Both elevated blood estrogen levels and an inactive lifestyle have been associated with an increased risk of breast cancer. Researchers of a study reported in the April 2004 issue of Cancer Research set out to determine the effect of exercise on circulating estrogens in sedentary women. A group of 173 inactive, overweight, post-menopausal women ranging in age from 50 to 75 years took part in the 12-month study.
The women were randomly assigned to a control group of non-exercisers or to a group that participated in moderate activity on average for 45 minutes, five days per week. Three months into the study, the exercisers had experienced a significant decrease in estrogen levels versus absolutely no change in estrogen levels for the non-exercisers. After 12 months the women who had decreased body fat by two percent or more, due to exercising, had decreases of 11.9 percent in serum estrone, 13.7 percent in estradiol, and 16.7 percent in free estradiol levels.
These findings led to the conclusion that increased physical activity may be associated with reduced risk of postmenopausal breast cancer because of its effects on serum estrogens.