Running and breast cancer survival
Jacob Schor ND, FABNO
March 7, 2014
A recent paper by Paul Williams that appeared in a January issue of the International Journal of Cancer will force me to change what I’ve been telling patients. For the past half dozen years, I have strongly encouraged breast cancer patients to walk daily based on data from Irwin et al’s 2007 paper that suggested a possible 45% reduction in death rate.  When patients have asked whether more exercise would be better, all I could do was shrug, we didn’t know and more of something that’s good for you is not necessarily better. Williams’ paper clears this up. It’s better for breast cancer patients to run than to walk for exercise.
Williams PT. Significantly greater reduction in breast cancer mortality from post-diagnosis running than walking. Int J Cancer. 2014 Jan 27. doi: 10.1002/ijc.28740.
Williams used Cox proportional hazard analyses to prospectively compare breast cancer mortality to baseline exercise energy expenditures and to test whether post-diagnosis running and walking differ significantly in their association with breast cancer mortality.
He analyzed data from 272 runners and 714 walkers from the National Runners' and Walkers' Health Studies who were previously diagnosed with breast cancer. Forty-six women (13 runners and 33 walkers) died from breast cancer during 9.1-years of the study. The survey data allowed the calculation of Metabolic Equivalent (METs) per hour per day and these were compared with risk of dying.
When data from runners and walkers were looked at together, the risk of dying from breast cancer decreased an average of 24% per metabolic equivalent (MET) hours per day of exercise, where one MET hour equals a little less than a mile of brisk walking or about two-thirds of a mile of running.
When the runners and walkers were analyzed separately, there was significantly lower mortality in the runners. The runners’ risk for breast cancer mortality decreased over 40% per MET hour per day. Runners that averaged over 2.25 miles running per day were at 95% lower risk for breast cancer mortality than those that did not meet current exercise recommendations. In contrast, the walkers’ risk for breast cancer mortality decreased only a non-significant 5% per MET hour per day, much less than Irwin had reported in 2007.
Physical activity may improve survival in women diagnosed with breast cancer, yet the evidence is not consistent. While a number of other studies have already shown physical activity significantly reduces breast cancer mortality [2-7], several other studies have not demonstrated a significant reduction [8-12]. Still, when data is combined via meta-analyses, there is stronger evidence for improved survival with greater physical activity. For example data from 13,302 breast cancer survivors of the After Breast Cancer Pooling Project suggest that meeting the current physical activity recommendations is associated with a 25% reduction in breast cancer mortality .
Meta-analyses that combine study results provide stronger evidence for improved survival. For example, Haskell et al reported that meeting the current physical activity recommendations has been associated with a 25% reduction in breast cancer mortality in 13,302 breast cancer survivors of the After Breast Cancer Pooling Project  .
(These recommendations for physical activity suggest that, “…all healthy adults aged 18 to 65 yr need moderate-intensity aerobic (endurance) physical activity for a minimum of 30 min on five days each week or vigorous-intensity aerobic physical activity for a minimum of 20 min on three days each week”  .)
Two other meta-analyses reached similar conclusions. Patterson et al found 29% (including lifetime and at diagnosis physical activity)  and Ibrahim et al found 34% reductions  in breast cancer mortality with post-diagnosis physical activity when various study results were combined.
There are aspects of this study that will be criticized, in particular the self-reporting by the participants, lack of information on cancer stage at diagnosis, type of breast cancer it was and what treatment the women underwent.
There is low risk of harm from encouraging more physical activity and encouraging greater exercise intensity in women who have been diagnosed with breast cancer. The possibility that such a simple intervention as running might prove useful as Williams’ study suggests is certainly intriguing. We now have reason, at least for the moment, to encourage certain patients, at least those who have been diagnosed with breast cancer, to take up running.
Reference: Williams PT. Significantly greater reduction in breast cancer mortality from post-diagnosis running than walking. Int J Cancer. 2014 Jan 27. doi: 10.1002/ijc.28740. [Epub ahead of print]
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