Breast Cancer? Get Walking!

Summarized by Robert W. Griffith, MD
September 2, 2005

Introduction

For some time it's been known that physical activity decreases the likelihood of developing breast cancer, but how about exercise after cancer has been diagnosed? Will it help prevent a recurrence? Physical activity has been linked to a lower level of circulating estrogen, so maybe it would help in the post-treatment phase. A study reported in the Journal of the American Medical Association has tried to clarify this important question, and we summarize the findings here.

What was done

The people involved in this study were almost 3,000 registered nurses in the Nurses' health Study who had been diagnosed with stage I, II, or III breast cancer between 1984 and 1988. They were followed up until they died or June 2002, whichever came first.

The nurses completed questionnaires about the amount of exercise they took; what sort of exercise, the intensity, and the average number of hours per week. The first physical activity questionnaire collected at least two years after the breast cancer diagnosis was used, to avoid assessments that might be influenced by active treatment of the cancer.

To be able to evaluate the effect of exercise, all physical activity reported was transformed into MET-hours per week (MET stands for Metabolically Equivalent Task). One MET is the energy expenditure for sitting quietly. Walking at an average pace has a MET score of 3; jogging, 7; and running, 12.

The nurses were classified as to their MET-hours per week into 5 groups: less than 3, 3-9, 9-15, 15-24, or 24 and above. The likelihood of death from cancer was assessed for each of these groups; then the Relative Risk was calculated for each group, setting the less than 3 MET-hours per week as "1".

What was found

There were 280 deaths from breast cancer, and 370 recurrences, among the 3,000 women. The relative risks of death from breast cancer for the different exercise groups are given in the table.

MET-Hours Per Week	Relative Risk (death)
Less than 3	1
3 to 9	0.80
9 to 15	0.50
15 to 24	0.56
24 and above	0.60

It was found that the greatest benefit was seen in women who performed the equivalent of walking 3 to 5 hours a week at an average speed. Increasing the frequency or intensity of exercise did not seem to increase this benefit.

The relative risks of a recurrence of cancer were also linked to the amount of physical activity, to a similar degree to those for death.

The relative risk associated with physical activity was lower (i.e. a better result) in women with stage III cancer (as opposed to stages I and II). And being overweight at the time of diagnosis and gaining weight after diagnosis was linked to poorer survival.

Women with hormone-responsive tumors also had a greater survival benefit form moderate physical activity.

What this means

Physical activity is not just for the overweight or cardiovascular patient. Breast cancer victims can also benefit from taking regular moderate exercise. Walking at a normal pace for 3 to 5 hours a week offers the best results, according to this study in 3,000 women. And it obviously will improve morale and the quality of life, as beneficial add-ons.

Source

• Physical activity and survival after breast cancer diagnosis. MD. Molmes, WY. Chen, D. Feskanich,  et al., JAMA, 2005, vol. 293, pp. 2479--2486

Related Links
Another Battle Won in the War Against Cancer?
A Few New Nuggets on a Very Scary Topic: Breast Cancer

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