Much research has shown a link between regular, moderately intense or vigorous exercise and a lower risk of breast cancer. While less intense exercise can benefit general health, this research suggests that lower-intensity exercise doesn't really lower breast cancer risk.
The study reviewed here found that only vigorous exercise was linked to a lower risk of breast cancer in post-menopausal women, and only when that exercise was done from mid-life onward.
This research was done in a collaboration between the National Institutes of Health (NIH) and AARP. Nearly 120,000 post-menopausal women, all AARP members between the ages of 50 and 71, completed a comprehensive health survey that included questions about levels of regular exercise activity over their lifetimes. During a period of over 6.5 years after completing the survey, the heath status of these women was followed. Over 4,200 women developed breast cancer during this follow-up period. The researchers compared the exercise histories of the women who did and did not develop breast cancer.
Key results:
The researchers caution that the reliability of these results may have been influenced by at least two important factors. First, only a small portion of the 3.5 million women who were invited to participate in the survey chose to participate. It is possible that factors that influenced the decision to participate may have resulted in a study group that doesn't truly represent all women. Second, the exercise levels were based on self-reporting from memory and not based on direct observation of actual exercise levels over time. Self-reporting can result in over-estimating and under-estimating actual exercise activity at points in the past.
While this article doesn't specify what types of exercise were considered vigorous in the survey, the following would be examples of vigorous exercise: running, fast jogging, scrubbing floors, and chopping wood. Examples of non-vigorous activities would be walking, washing clothes, and mowing the lawn.
Along with healthy diet and lifestyle choices, regular exercise is one of the best steps ALL WOMEN can take to help keep breast cancer risk as low as it can be. This and other studies suggest that the more intense the exercise, the more likely the reduction in breast cancer risk. Regular exercise also helps keep your general health the best that it can be. No matter how old you are, it's never too soon or too late to get moving.
Regular moderate-to-vigorous exercise may reduce breast cancer risk for postmenopausal women, researchers found.
Postmenopausal women who maintained more than seven hours per week of higher intensity activity over the 10-year period prior to entry into the study were 16% less likely to develop breast cancer (RR 0.84, 95% CI 0.76 to 0.93), according to Tricia M. Peters, MPhil, of the National Cancer Institute in Bethesda, Md., and colleagues.
But their prospective National Institutes of Health-AARP Diet and Health Study, reported online in BMC Cancer, did not reveal reductions in risk with light activity or with more intense exercise earlier in life.
The findings dovetail with the consistent reductions in postmenopausal breast cancer observed with greater levels of physical activity, but help pin down the protective effect.
The reason for differences by recency and level of activity, Peters' group said, could be the biological mechanisms proposed for the link: alteration of levels of endogenous sex hormones, modulation of insulin and insulin-like growth factors, enhanced immunity, and reduced chronic inflammation.
The NIH-AARP study included 118,899 postmenopausal women who completed detailed questionnaires sent to the 3.5 million AARP members who were 50 to 71 years old and lived in six states or the Atlanta or Detroit metropolitan areas.
The levels of physical activity at different times of their lives came from the answers to the questionnaires at the time participants entered the study.
During 6.6 years of follow-up, these women were diagnosed with a total of 4,287 incident breast cancers, mostly estrogen receptor-positive tumors (84%).
Physical activity at any intensity level from ages 15 to 18, from 19 to 29, and from 35 to 39 had no impact on postmenopausal breast cancer risk.
Walking, golfing, gardening, and other light-intensity activities were more common than higher intensity activity throughout the lifespan.
Still, light-intensity activity in the past didn't impact risk in the age-adjusted model even at the highest participation level for the recent decade (RR 1.04 with more than seven hours of exercise per week versus inactivity, 95% CI 0.89 to 1.21).
Women typically reported spending more time in moderate-to-vigorous activities such as swimming, tennis, and jogging before age 40 than they did in the 10 years before the survey. But only activity in that decade was linked to breast cancer risk.
At the highest level of participation in moderate-to-vigorous activity, with an average of more than seven hours per week over the prior decade, breast cancer risk was 16% lower than it was among inactive women, after adjustment for age and multivariate adjustment (both RR 0.84, 95% CI 0.76 to 0.93).
Further controlling for body mass index in middle age had little effect on the link between higher-intensity activity and breast cancer risk (RR 0.87, 95% CI 0.78 to 0.96), suggesting an independent effect, the researchers said.
This effect of regular, recent moderate-to-high intensity exercise was only significant for risk of estrogen receptor-positive tumors (RR 0.77, 95% CI 0.64 to 0.92), but the relationship with the much less commonly observed estrogen receptor-negative tumors was of a similar magnitude (RR 0.87, 95% CI 0.58 to 1.29).
The researchers said the findings were likely to apply to the general population, in part because of the similarity between the rates of women who reported at least 2.5 hours a week of moderate-to-vigorous activity: 49% in their cohort versus 47.5% in a national survey.
They cautioned, however, that participants might be more accurate in recalling activity that was recent or more intense than exercise that was lighter or in the distant past.
Also, they noted that a low participation rate among the large population who received surveys may affect generalizability of the findings.
The research was supported by the Intramural Research Program of the NIH, National Cancer Institute. The researchers provided no information on conflicts of interest.
Primary source: BMC Cancer Source reference: Peters TM, et al "Intensity and timing of physical activity in relation to postmenopausal breast cancer risk: the prospective NIH-AARP Diet and Health Study" BMC Cancer 2009; DOI: 10.1186/1471-2407-9-349.
Breastcancer.org 7 East Lancaster Avenue, 3rd Floor Ardmore, PA 19003
Learn more about our commitment to your privacy
© 2009 Breastcancer.org - All rights reserved.
Breastcancer.org is a non-profit organization dedicated to providing information and community to those touched by this disease. Learn more about our commitment to providing complete, accurate, and private breast cancer information.
