Exercising vigorously for 60 rather than 30 minutes five times a week helps women aged 50 and older lose more body fat and have trimmer waistlines, but not enough to have much of an effect on their risk of breast cancer, according to a study published recently in the journal JAMA Oncology.
Still, this study’s findings can be viewed as encouraging for older women who have been following the current minimum physical activity recommendations of health officials (30 minutes of brisk walking or other moderate-intensity aerobic activity five times a week), but have wondered if it would be worthwhile to exercise more.
That answer may be yes. For women gain other health benefits when they shed excess body fat, including a lower risk of heart disease and type 2 diabetes.
And even if you don’t lose weight, regular aerobic exercise is likely to improve your health and well-being as you age — by strengthening your heart, keeping your arteries clear, boosting your mood, increasing your physical stamina, and helping you stay active and independent.
For the study, a team of researchers led by Christine Friedenreich, a cancer researcher at the University of Calgary in Canada, randomly assigned 400 women aged 50 to 74 to either 30 minutes or 60 minutes of exercise five times a week for 12 months.
All the women had been relatively inactive before the study began. Their body mass index (BMI) ranged from 22 (“normal”) to 40 (“morbidly obese”). They were all nonsmokers and had never taken menopausal hormone therapy. Nor had any of them been diagnosed with any kind of cancer or other serious illness.
The women were sent to a community fitness center three times a week, where they worked out under the supervision of a trainer. They exercised on their own the other two days a week.
The women were instructed to exercise vigorously — at 65 percent to 75 percent of their maximum heart rate — during at least half of their workouts each week. Most of the time, the women chose to meet this goal by walking, running, biking or using an elliptical machine.
The women were not instructed to alter their diets in any way.
After the 12 months were up, the women in the 300-minute-a-week-group had, on average, lost about 1 percent more of their total body fat than those in the 150-minute-a-week group. The 300-minute-a-week group also lost more subcutaneous abdominal fat and total abdominal fat, and they ended up with slightly smaller waistlines, on average, than the women in the other group.
All of these differences were significant but small, particularly given that the women had been exercising for a full year.
The waistline difference is especially interesting, however. Some research has suggested that having a too-big waistline (more than 35 inches for women) is a stronger risk factor than BMI for chronic disease and early death.
Little effect on breast cancer risk
Friendenreich and her colleagues undertook this study to see if they could determine how much exercise to prescribe to older women to help them lower their risk of breast cancer. After menopause, women’s risk of developing this cancer rises significantly, perhaps because of weight gain, some research suggests.
But, as Kerri Winters Stone, a research professor at Oregon Health and Science University, notes in an editorial that accompanies the study, the difference in weight loss between the groups in the study was not great enough to base any strong recommendations on it.
“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,” she writes.
This was especially true of women who entered the study with a BMI under 30. They tended to lose about the same percentage of body fat whether they exercised 150 or 300 minutes a week.
Bigger differences were seen among the women with BMIs of 30 or more. Those who exercised for 300 minutes a week lost, on average, twice as much body fat as those who exercised for only 150 minutes. The difference equates to an estimated 5.5 percent reduction in the relative risk of breast cancer.
But that’s still a very small reduction in risk.
You can download and read the study in full at the JAMA Oncology website.