NEW YORK (Reuters Health) - Middle aged women who get a few hours of activity each week, including walking or more vigorous exercise, are less likely to be diagnosed with breast cancer than more sedentary women, according to a new study from France.
“The women who recently, in the previous four years, performed physical activity had a decreased risk of breast cancer compared with women who were not so active,” said coauthor Françoise Clavel-Chapelon. But that decrease disappeared after the physical activity stopped, she added.
“We looked at recreational physical activity and even if it’s of modest intensity, let’s say, it had rapid impact on breast cancer risk,” Clavel-Chapelon, at the Institut Gustave-Roussy in Villejuif, told Reuters Health by phone.
Of the 59,308 postmenopausal women followed between 1993 and 2005 in the study, most were teachers and 2,155 were diagnosed with invasive breast cancer.
According to questionnaires they filled out once every two years during that period, the women who were most active were less likely to be diagnosed with breast cancer.
Those who reported walking for at least four hours a week or doing more vigorous exercise, like cycling, for at least two hours a week were least likely to be diagnosed with breast cancer, according to the results in Cancer Epidemiology, Biomarkers & Prevention.
That apparent benefit was limited to exercise within the previous four years, the researchers found, and exercise five to nine years in the past had no effect on risk.
High levels of recent physical activity were associated with a 10 percent decrease in risk for breast cancer. Since the group as a whole had a 3.6 percent risk of breast cancer, with the full benefit of exercise that risk would fall to 3.3 percent.
This study is observational, so no group of women was actually given an exercise prescription and researchers can’t say for sure that being active is what lowered the risk of breast cancer. But there have been over a hundred other studies on physical activity and breast cancer risk with similar results, said Christine Friedenreich.
“It does seem like there’s a lot of consistency and strength in the evidence, and there are plausible biological mechanisms for what’s going on,” she said. Keeping active helps reduce body fat, too much of which is an important risk factor for breast cancer, she said.
Friedenreich, of the department of Cancer Epidemiology and Prevention Research of CancerControl Alberta in Calgary, was not involved in the new study.
The mechanism is likely not hormonal, Clavel-Chapelon said, because results did not differ by type of breast cancer, but it could have to do with inflammation or immune response, or of course weight control, she said.
“We actually conducted a study in 2001, a population-based case-control study measuring lifetime physical activity,” Friedenreich told Reuters Health by phone. Activity levels after menopause, whether or not the woman had been active earlier in her life, were most important in predicting breast cancer risk, she said.
When a woman went from sedentary to active after menopause, her breast cancer risk decreased by 40 percent. One who had exercised regularly for life decreased her risk by 42 percent compared to a non-exerciser, Friedenreich said.
“It’s never too late to start being physically active even if you have never been physically active before,” she said.
Spending more time per week on less intense activity seemed to offer the same benefit as shorter periods of more intense activity, Clavel-Chapelon noted, but Friedenreich still favors more vigorous activity.
“We don’t know the exact exercise prescription to give these women yet, but we’re trying to answer that question,” Friedenreich said. In any case, physical activity level is one of the most important modifiable risk factors for breast cancer, she said. Other important factors, like genetics and age at menopause, can’t be changed.
SOURCE: bit.ly/1oufbQr Cancer Epidemiology, Biomarkers & Prevention, online August 11, 2014.