Many research studies have delved into relationships between exercise and various forms of cancer. While individual study results have been mixed, the big meta-analyses have generally found a connection between exercise and low cancer incidence or high cancer survival.
This is particularly true for breast cancer, perhaps the most studied cancer. However, no one had looked at breast-cancer survival through the lens of vigorous vs. moderate exercise.
Enter Paul Williams, Ph.D., the prolific researcher who maintains the databases for the National Runners Health Study and the National Walkers Health Study. Williams has just published his latest report in the International Journal of Cancer.
It compares breast cancer survival rates between runners and walkers. Runners are considered vigorous exercisers because they produce greater than 6 METs/hour, while walkers are in the moderate zone, usually at 3-5 METs/hour. METs are a measure of energy expenditure favored by Williams and other researchers because they allow comparisons among many activities. METs/hour is greater for running than walking because most runners, even slow runners, maintain a pace of 12:00 minutes per mile, or faster. Most walkers use a pace of 17:00 to 20:00 minutes per mile, or slower.
Result: The runners enjoyed “significantly greater reductions in breast cancer mortality.” Specifically, breast cancer mortality decreased a statistically significant 40.9% per MET/hours a day among the runners, and a non-significant 4.6% among walkers per MET/hours a day. In other words, for the same energy expenditure, whether you measure total calories burned or MET/hours, runners get much more breast cancer survival benefit than walkers.
The more the runners trained, the greater their reduction in breast cancer mortality. Those who ran in the range of 15.6 miles/week or more had a 95.4% lower mortality than those who ran 4.4 miles/week or less. Williams notes that the hard-training runners exceeded the optimal weekly exercise recommendations (75 vigorous minutes/week) of many national authorities.
The results are a little surprising, as many of Williams’s recent papers have found equivalent benefits for runners and walkers exercising equivalent amounts. For example, he has found this to be true for incidence of high blood pressure, high cholesterol, diabetes, and coronary heart disease, among other conditions.
Williams says there are now two exceptions to the equivalency findings: Running beats walking for breast cancer survival and for weight control.
Williams’ studies always produce reams of statistics. In the new study, he notes the following concerning risk factors for breast cancer mortality:
“When adjusted for age, race and exercise, the risk for breast cancer mortality was significantly associated with menopausal status, family history, years of contraceptive use, lactation, and bra cup size, but not with education, smoking, BMI, body circumference, age of menarche, nulliparousness, number of live births, baseline use of oral contraceptive, or baseline estrogen/progesterone hormone use, years since breast cancer diagnosis, or intakes of meat, fruit, and alcohol.”
The new breast cancer study followed 272 runners and 714 walkers for an average of 9.1 years. Their breast cancer diagnosis occurred 8 years before they enrolled in the study. Forty-six women died from breast cancer during the study period.
“In conclusion,” writes Williams, “we have shown that breast cancer mortality in post-diagnosis runners may be lower than that in post-diagnosis walkers, and that exceeding the public health recommendation for physical activity was better than merely achieving it.”