Clinical Trail Shows 300 Minutes A Week Of Exercise Will Cut Postmenopausal Breast Cancer Risk

Doubling the amount of weekly moderate to vigorous aerobic exercise, to 300 minutes instead of 150 minutes a week, had a better effect on body fat in a trial of 400 inactive postmenopausal women.

Reducing total fat and other adiposity measures, especially for obese women, was more effective with the greater exercise during a 1-year clinical trial published in JAMA Oncology.

The finding is noteworthy, say the authors, because body fat has been associated with increased risk of postmenopausal breast cancer, so these women may derive unique benefit from exercise.

Physical activity is an inexpensive, noninvasive strategy for disease prevention.

Worldwide, public health agencies recommend that for overall health we be physically active for at least 150 minutes a week at moderate intensity, or 60-75 minutes a week at vigorous intensity.

The authors led by Christine Friedenreich, PhD, of Alberta Health Services in Edmonton, Alberta, Canada, conclude: “In previously inactive postmenopausal women, a 1-year prescription of moderate to vigorous exercise for 300 minutes/week was superior to 150 minutes/week for reducing total fat and other adiposity measures, especially in obese women.” They add:

“These results suggest additional benefit of higher-volume aerobic exercise for adiposity outcomes and possibly a lower risk of postmenopausal breast cancer.”

For the study, the women with body mass indexes (BMI) between 22 and 40 were asked not to change their usual diet.

Any aerobic activity that raised heart rate to 65-75% of heart rate reserve was permitted during the trial.

Participants met one-to-one with a study exercise trainer in the first two sessions, receiving orientation to the training facility and a variety of aerobic equipment, including:

• Treadmills
• Stationary bicycles
• Elliptical trainers.

Trainers also provided a comprehensive exercise educational guide that included home-based exercise examples and technique instructions for specific activities.

Effects on a number of measures

Average reductions in total body fat were 1 kg (1% of body fat) larger in the 300-minute exercise group compared with the 150-minute group.

Decreases were also larger for the following measures in the 300-minute group:

• Subcutaneous abdominal fat
• Total abdominal fat
• BMI
• Waist circumference
• Waist-to-hip ratio.

The results show that there were stronger effects for women who were obese – had a BMI of 30 or more – against the measures for change in weight, BMI, waist and hip circumference, and subcutaneous abdominal fat.

The authors conclude: “A probable association between physical activity and postmenopausal breast cancer risk is supported by more than 100 epidemiological studies, with strong biologic rationale supporting fat loss as an important (though not the only) mediator of this association.

“Our findings of a dose-response effect of exercise on total fat mass and several other adiposity measures including abdominal fat, especially in obese women, provide a basis for encouraging postmenopausal women to exercise at least 300 minutes/week, longer than the minimum recommended for cancer prevention.”