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Lifelong Physical Activity Lowers Breast Cancer Risk

Lifelong Physical Activity Lowers Breast Cancer Risk

ORLANDO—Women in all ethnic groups who have spent their lives exercising,
performing heavy household chores, or tackling a physically strenuous job had
a lower risk of breast cancer than their more sedentary counterparts,
according to a poster presented at the Era of Hope Department of Defense
Breast Cancer Research Program meeting. "We were pleased with the results,"
said principal investigator Esther M. John, PhD, director of epidemiology
research, Northern California Cancer Center, Union City. "It’s a message we
can give women to help prevent breast cancer, and there are other health
benefits to physical activity."

The researchers personally interviewed 1,326 women, aged 35 to 79,
diagnosed with invasive breast cancer between 1995 and 1998, and 1,657
controls found through random-digit dialing. The cohorts were equally
divided, with approximately one third each Hispanic, non-Hispanic white, and
African American. All came from the San Francisco Bay area.

The women were asked about moderate and vigorous physical activity,
including participation in sports, if they walked or bicycled to school or
work, exercise, household and outdoor chores, and occupational activities.
Responses from all the categories were combined to arrive at an average
measure of physical activity.

Among the women who had the highest level of physical activity,
premenopausal women had a 26% lower risk of breast cancer and postmenopausal
women a 19% lower risk, Dr. John reported. Women who were not overweight
(body weight index of 25 or less) had a slightly greater risk reduction than
overweight women. Risk reduction was not limited to vigorous exercise but was
also present for moderate activity. Risk reduction results in the three
ethnic groups were similar for similar amounts of activity.

Hispanic women had the highest level of lifetime physical activity,
followed by African Americans and non-Hispanic whites, Dr. John said.

She noted that Hispanic women have a lower incidence of breast cancer: In
the San Francisco Bay area during the years of the study, the rates per
100,000 for women aged 35 to 49 were 90 for Hispanics, 105 for African
Americans, and 135 for non-Hispanic whites.

Dr. John estimated that differences in physical activity could explain a
small percentage (13%) of the difference in breast cancer incidence between
Hispanic and non-Hispanic white women younger than age 50. But physical
activity was not a factor in the incidence disparity between African-American
women and non-Hispanic white women.

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