By Suzanne Dixon, MPH, MS, RD
Healthnotes Newswire (March 19, 2009)—Regular exercise is important for good health, staving off everything from osteoporosis to heart disease. When it comes to breast cancer, however, health experts haven’t yet agreed on whether exercise truly reduces risk. Studies on this topic are mixed, but new research helps explain why. By considering all types of breast cancer as one single disease and by lumping together physical activity at all points during a woman’s life, researchers have missed important connections between these two factors.
What, when, how
Health experts know that not all breast cancers are the same. For example, some breast cancers will grow more quickly in response to the presence of naturally-occurring hormones in the body, such as estrogen and progesterone, and are referred to as estrogen receptor positive (ER+) and/or progesterone receptor positive (PR+) breast cancers. Breast cancers that do not respond to these hormones are referred to as estrogen receptor negative (ER-) and/or progesterone receptor negative (PR-) cancers. These differences are important because they help researchers understand why a woman might develop breast cancer and they help doctors best treat each unique breast cancer when it does occur.
German researchers studied 3,414 postmenopausal women with breast cancer (cases) and 6,569 women without breast cancer (controls) to determine how physical activity at different times in a woman’s life affects her risk of different breast cancer types. The women were asked about recreational and nonrecreational (job and household activities) physical activity between ages 30 and 49 and after age 50.
The researchers found that women who reported the highest levels of recreational physical activity (exercise) after age 50 reduced their risk of developing post-menopausal, ER+/PR+ breast cancer, which is the most common type, by 29% compared with women performing the least physical activity after 50. Any type of physical activity, recreational or not, between ages 30 and 49 did not seem to have an effect on postmenopausal breast cancer risk. For breast cancer types other than ER+/PR+, regular physical activity did not lower risk either.
About 75% of all breast cancers are ER+ and two-thirds of those are also PR+. This means that regular physical activity after age 50, even if a woman has never exercised much in the past, can reduce her risk of developing the most common type of breast cancer by nearly one-third.
How much is enough?
In this study, the highest physical activity group performed the equivalent of about 2.5 hours of moderate-pace walking daily. This may seem like a lot of exercise, but fortunately, how the women undertook the activity didn’t seem to matter. The 2.5 hours of walking is simply for comparison purposes. The researchers simply summed up all recreational activity, which supports the notion that you don’t need to get all of your daily physical activity at once. Small, regular bouts of physical activity, such as walking, gardening, or playing with your kids or grandkids all count. As well, the researchers noted a trend of decreasing incidence of breast cancer with increasing amount of exercise, which tells us that any exercise is better than none. For best benefit, however, aim for as much exercise as you can fit in each day.
What are the most important take home messages from this research?
1. It’s never too late to improve your health with regular exercise.
2. Be active in all possible ways for good health.
(Cancer Epidemiol Biomarkers Prev 2008;17:3402–10)
Suzanne Dixon, MPH, MS, RD, an author, speaker, and internationally recognized expert in chronic disease prevention, epidemiology, and nutrition, has taught medical, nursing, public health, and alternative medicine coursework. She has delivered over 150 invited lectures to health professionals and consumers and is the creator of a nutrition website acclaimed by the New York Times and Time magazine. Suzanne received her training in epidemiology and nutrition at the University of Michigan, School of Public Health at Ann Arbor.
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