Increased Physical Activity Associated with Reduced Risk for Breast Cancer in Postmenopausal Women

Last Updated: Oct. 1, 2003

Longer duration provides most benefit; activity need not be strenuous

Anne McTiernan, M.D., Ph.D., of the Fred Hutchinson Cancer Research Center, Seattle, and colleagues examined the association between recreational physical activity in adulthood and breast cancer incidence in a large, ethnically and racially diverse cohort of older women from the Women's Health Initiative (WHI) Observational Study.

Using detailed assessments of physical activity, the researchers assessed the associations between physical activity (past strenuous activity at ages 18, 35, and 50 years, and current total physical activity score, hours per week of strenuous activity, and combined hours per week of moderate and strenuous activity) and incidence of breast cancer. The study included 74,171 women aged 50 to 79 years who were recruited by 40 U.S. clinical centers from 1993 to 1998.

The researchers documented 1,780 newly diagnosed cases of breast cancer over an average follow-up of 4.7 years. “Compared with less active women, women who engaged in regular strenuous physical activity at age 35 years had a 14 percent decreased risk of breast cancer. Similar but attenuated findings were observed for strenuous physical activity at ages 18 years and 50 years. An increasing total current physical activity score was associated with a reduced risk for breast cancer. Women who engaged in the equivalent of 1.25 to 2.5 hours per week of brisk walking had an 18 percent decreased risk of breast cancer compared with inactive women. Slightly greater reduction in risk was observed for women who engaged in the equivalent of 10 hours or more per week of brisk walking."

The effect of exercise was most pronounced in women in the lowest body weight group.

Moderate Exercise as Effective as Vigorous Exercise in Initial Weight Loss when Combined with Decreased Calorie Intake
Exercising longer or with greater intensity will not significantly increase the amount of weight lost for women who are dieting and exercising, according to an article in the September 10, 2003 issue of The Journal of the American Medical Association (JAMA).

According to background information in the article, an estimated 60% to 65% of adults in the United States are overweight. Exercise is an important component of interventions targeting overweight and obese adults, and is important for improving short-term weight loss when combined with changes in dietary intake; and is one of the best predictors of long-term weight loss.

However, the optimal amount of exercise necessary to enhance long-term weight loss has not been established. But it has been believed that a higher dose and intensity of exercise may improve long-term weight loss.

John M. Jakicic, Ph.D., of the University of Pittsburgh, Physical Activity and Weight Management Research Center, Pittsburgh, and colleagues examined the effect of exercise of varying duration (moderate vs. high, about 150 minutes/week to 200 minutes/week) and intensity (moderate vs. vigorous) on weight loss and cardiorespiratory fitness following 12 months of treatment in overweight adult women.

“Weight loss was significant within all groups, but there was no significant effect of either exercise duration or exercise intensity on changes in body weight between groups,” the authors write.

“The results of this study have implications for prescription of exercise for sedentary, overweight adults engaging in weight loss efforts. Our results suggest that moderate to high levels of exercise used in combination with a decrease in calorie intake resulted in 8 percent to 10 percent reductions in body weight following a 12-month intervention. Moreover, participants randomized to vigorous exercise intensity did not have greater weight loss than those randomized to a similar dose of exercise performed at a moderate intensity," the researchers write.

“However, when data were analyzed based on the amount of exercise performed, greater levels of exercise were associated with a greater magnitude of weight loss following 12 months of treatment. Thus, interventions should initially target the adoption and maintenance of at least 150 minutes per week of moderate intensity exercise, and when appropriate, eventually progress to exercise levels consistent with the Institute of Medicine’s recommendation.”

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