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29-03-2010 | Oncology | Article

Hormonal changes may mediate physical activity benefits on postmenopausal breast cancer risk


Free abstract

MedWire News: Researchers have found hormonal changes consistent with a reduced risk for breast cancer in previously sedentary postmenopausal women who participated in a year-long aerobic exercise program.

Specifically, the exercise program resulted in reduced estradiol and free estradiol and increased sex hormone-binding globulin (SHBG) serum concentrations.

“Consistent observational epidemiologic evidence suggests that physical activity is associated with reduced postmenopausal breast cancer risk,” note Christine Friedenreich (Alberta Health Services, Calgary, Canada) and colleagues.

In the present study, Friedenreich and team examined how an aerobic exercise intervention influenced circulating levels of estradiol, estrone, SHBG, androstenedione, and testosterone – factors that may be involved in the association between physical activity and breast cancer risk.

The researchers carried out a two-center, randomized controlled trial of exercise in 320 postmenopausal, sedentary women aged 50 to 74 years. The women were randomly assigned to a 1-year aerobic exercise intervention of 225 minutes/week (n=160) or to a control group who maintained their usual level of activity (n=160). Hormone levels were measured at baseline and at 6 and 12 months.

Friedenreich et al report that women in the exercise group exercised an average of 3.6 days/week for a total of 178 minutes/week.

At 12 months, women in the exercise group had a significant 7% reduction in estradiol, 9% reduction in free estradiol, and a 4% increase in SHBG compared with the control group.

Greater adherence to the exercise program was also associated with greater decreases in estradiol concentration and increases in SHBG concentration.

No significant differences in estrone, androstenedione, or testosterone levels were observed between exercisers and controls at 12 months.

“This trial provides new evidence that previously sedentary, mostly overweight, postmenopausal women can achieve and sustain high levels of aerobic exercise that result in statistically significant changes in estradiol and SHBG concentrations that are consistent with a reduced risk of postmenopausal breast cancer,” Friedenreich and co-authors conclude in the Journal of Clinical Oncology.

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Laura Dean

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