Even moderate physical activity -- for example brisk walking for at least 2 miles three times a week -- over the course of a lifetime can reduce a young woman's risk of developing breast cancer by 33%, and the risk of breast cancer after menopause by 26%, according to results of a study of women living in the San Francisco Bay area.

The study confirms earlier reports that exercise can reduce the risk for breast cancer. This study also points out two important factors: it is total physical activity over the course of a lifetime that confers a benefit, and this activity is not limited to vigorous exercise. Even moderate activity has real benefits.

Dr. Esther M. John, an epidemiologist at the Northern California Cancer Center in Union City, California based the findings on interviews with 1,249 women aged 35 to 79 who were newly diagnosed with breast cancer between 1995 and 1998, and 1,547 similar women who were cancer-free.

Of the women with breast cancer. 402 were diagnosed before menopause and 847 were diagnosed after menopause. The risk of breast cancer increases with age.

The women agreed to detailed interviews that assessed total physical activity "beginning in the teen years and then continuing through every decade thereafter. We asked about all types of activity including traditional exercise like biking, running, walking and weight lifting and so on, as well as nontraditional exercise such as housework and yard work," she said. The women were asked, for example, if they walked to school as teens or if they rode bikes for pleasure or to run errands. Women were also asked to rate their jobs for exercise content.

The researchers then divided the women into three groups based on their activity level.

Those premenopausal women in the most active group had a 26% lower risk of breast cancer compared with the least active women. Postmenopausal women in the most active group had a 19% lower risk than the least active women.

Breast cancer risk was cut by 33% in premenopausal women who were moderately active and 26% in postmenopausal women who were moderately active compared with the least active women.

The benefits were greater for women with a lower body mass index (BMI), which probably indicated greater overall fitness. Women with a BMI of 25 or less who were in the most active group were 47% less likely to develop premenopausal breast cancer and 31% less likely to develop breast cancer after menopause than the most sedentary women. Anyone with a BMI 25 or more is considered overweight, while a BMI of 30 or more is considered to be obese.

Department of Defense Breast Cancer Research Program September 28, 2002 Orlando, FA

Dr. Mercola's Comments:

There's no shortage of literature documenting how exercise lowers the risk of cancer, and how a history of exercise can improve your chances of recovery once you've been diagnosed with cancer.

One of the major ways exercise benefits the body is by reducing insulin levels. It's quite clear that elevated insulin levels are associated with an increased risk of cancer.

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