Many studies have shown a link between exercise and a lower risk of being diagnosed with a first breast cancer or breast cancer coming back (recurrence). As a result, the American Cancer Society and many doctors recommend that women who’ve been diagnosed with breast cancer exercise regularly -- about 150 minutes per week at a moderate intensity level or 75 minutes per week at a vigorous level.
A new study suggests that exercising twice the recommended amount -- for a total of 300 minutes per week -- is better for shedding fat, especially in postmenopausal women.
The research was published online on July 16, 2015 by JAMA Oncology. Read “Effects of a High vs Moderate Volume of Aerobic Exercise on Adiposity Outcomes in Postmenopausal Women: A Randomized Clinical Trial.”
Being overweight -- defined as having a BMI (body mass index) over 25 -- increases the risk of breast cancer (and breast cancer recurrence for women who’ve been diagnosed), especially after menopause. This higher risk is because fat cells make estrogen; extra fat cells mean more estrogen in the body, and estrogen can make hormone-receptor-positive breast cancers develop and grow.
So many doctors were interested in the results of this study because it suggests that more exercise can reduce body fat.
In the study, called the Breast Cancer and Exercise Trial in Alberta (BETA), researchers evenly split 400 postmenopausal women who didn’t exercise into two groups:
- One group, called the moderate-volume exercise group, did aerobic exercise 5 days a week for 30 minutes (3 days were done under the supervision of a trainer and 2 were done on their own).
- The other group, called the high-volume exercise group, did aerobic exercise 5 days a week for 60 minutes (again, 3 days were done under the supervision of a trainer and 2 were done on their own).
The women exercised this way for 12 months. In most cases, the women used elliptical trainers, ran, walked, or rode bikes for their exercise.
The women were asked not to change their diet and eat as they always did.
The study took place between 2010 and 2013.
All the women had a BMI between 22 and 40, had not taken hormone replacement therapy, did not smoke, and had never been diagnosed with cancer or other major disease. During the study, 16 women dropped out (five from the high-volume exercise group and nine from the moderate-volume exercise group), so 384 women were included in the final analysis.
The researchers wanted to see if more exercise would lead to less total body fat. They also wanted to compare subcutaneous- (under the skin) and intra-abdominal fat levels, as well as the weight, and waist and hip measurements of the women before the study started and after it ended.
Overall, women in the high-volume exercise group:
- lost more total body fat, subcutaneous- and intra-abdominal fat
- lowered their BMI more
- reduced their waist and hip measurements more
compared to women in the moderate-volume exercise group.
The researchers found that the effects of more exercise were stronger in women who were obese when the study started:
- women with BMIs lower than 30 lost about 4 pounds, no matter which exercise group they were in
- women with BMIs of 30 or higher lost about 8.5 pounds in the high-volume exercise group
- women with BMIs of 30 or higher lost about 4 pounds in the moderate-volume exercise group
Still, how much breast cancer risk reduction does this fat loss translate into?
In an editorial accompanying the article, Kerri Winters-Stone, Ph.D., of the Knight Cancer Institute at the Oregon Health and Science University, wrote, “In the context of breast cancer, the degree of fat loss experienced by women exercising nearly 100 minutes more per week only equated to an estimated 2% further reduction in risk of breast cancer -- probably not enough to motivate women to add more than an hour and a half more exercise to their weekly schedule."
Still, while this study looked only at the ability of exercise to reduce fat, there may be more risk-reducing benefits to exercise than just fat loss. Exercise also can:
- reduce levels of proteins that cause inflammation
- increase levels of hormones linked to metabolism
- reduce DNA damage
all of which could reduce cancer risk. Exercise also helps you build muscle; certain proteins made by muscles also help reduce inflammation.
While this study alone may not be enough to convince women to exercise 300 minutes a week, future studies could look at the other risk-reducing benefits of exercise and add more evidence.
If you’re busy with work, household chores, and family matters, finding time to exercise almost every day can be hard. Exercising also can be extremely difficult if you’re recovering from breast cancer treatment. Still, it’s worth your while to make time to move.
It can help to break up your exercise into 20- or 30-minute sessions that add up to about 5 hours per week. Walking is a great way to start. Maybe you walk 30 minutes before going to work and 20 minutes on your lunch break. You can add a few more minutes by parking farther away from your building or taking mass transit. Or you can make plans to walk with a friend after work -- you’re more likely to stick with exercise if someone else is counting on you. Plus, you can socialize at the same time.
Along with a healthy diet and lifestyle choices, regular exercise is one of the best things women can do to keep the risk of a first-time breast cancer or recurrence as low as it can be. This study adds to other research suggesting that regular exercise reduces breast cancer risk. Regular exercise also helps keep your physical and mental health in top shape. No matter how old you are, it’s never too late or too soon to get moving.
Visit the Breastcancer.org Exercise section for tips on exercising safely and how to stick to an exercise routine.