Many studies have shown a link between regular moderate-to-intense exercise and lower breast cancer risk. Some researchers think that doing regular intense exercise lowers breast cancer risk by reducing estrogen levels. Since estrogen can cause breast cancer cells to develop and grow, less estrogen in the body could lower breast cancer risk.
A study found that postmenopausal women who regularly did intense exercise for a year had lower levels of estradiol, a type of estrogen, compared to women who didn't exercise.
Before joining the study, most of the 320 postmenopausal women age 50 to 74 were overweight and did very little or no exercise. The women were randomly split into two groups:
- Half the women kept up their usual level of activity during the 1-year study.
- Half the women did intense aerobic exercise for about 225 minutes (4 hours and 45 minutes) each week during the study.
The women in the exercise group usually worked out for about 45 minutes 3 to 5 days per week. At least three sessions each week were done with trainers at a fitness center and the rest of the exercise was done at home. The exercise was intense and raised the women's heart rates to a target level above resting heart rate.
The researchers measured the women's levels of several hormones and a related protein at the beginning of the study, in the middle of the study (6 months), and at the end of the study (1 year).
At the end of 1 year, the levels of two types of estrogen were lower in the women in the exercise program compared to the women who kept up their usual activity level.
- estradiol levels were about 7% lower in the exercise group
- free estradiol levels were about 9% lower in the exercise group
The results didn't show a lower risk of breast cancer, but the researchers think that the lower estrogen levels might be enough to reduce risk. Some experts who studied the results think that the small reduction in estrogen levels may not be enough to reduce breast cancer risk. Some hormonal therapy medicines used to reduce the risk of breast cancer coming back (recurrence) lower estrogen levels much more than exercise did in this research. Still, other research has shown a link between regular intense exercise and lower breast cancer risk.
Along with healthy diet and lifestyle choices, regular exercise is one of the best things all women can do to keep breast cancer risk as low as it can be. This study adds to other research suggesting that higher intensity exercise reduces breast cancer risk more than light or moderate exercise. Regular exercise also helps keep your physical and mental health in top shape. No matter how old you are, it's never too soon or too late to get moving.
Visit the Breastcancer.org Nutrition pages for tips on creating a healthy eating plan that includes exercise.