Research has shown that physical activity can lower a person's risk of developing cancer and increase the rate of survival. A new study led by Dr. Neli Ulrich in the Public Health Sciences Division reveals one reason may be because exercise reduces inflammation, a suspected culprit behind many chronic diseases.
Ulrich and colleagues found that menopausal, overweight women who engaged in a regular, moderate-intensity exercise program significantly lowered their levels of C-reactive protein (CRP) and serum amyloid A (SAA). Both are signals for inflammation that have been associated with increased cancer risk and decreased survival and also have been linked to increased risk of heart disease.
Ulrich presented the results of the study at the 95th Annual Meeting of the American Association of Cancer Research last month in Orlando, Fla.
"What motivated us to do the study was to see what exactly it is about exercise that makes it reduce cancer risk or improve survival," she said. "We know that regular exercise can reduce the amount of fat in the body. Fat cells can do a lot of things — for example they produce estrogen and they can also secrete substances that signal the presence of an inflammation. So we decided to measure blood markers of inflammation, such CRP, to help us understand how exercise may affect cancer risk and survival."
Rising risk factors
Inflammation markers like CRP typically rise dramatically during the course of an infection or as part of an inflammatory disease. Levels of CRP above 3 milligrams per liter are a risk factor for cardiovascular disease.
Recent studies show CRP can also be a risk factor for colon cancer, Ulrich said.
"Studies have suggested that low-grade inflammation can enhance cancer development — although the exact reasons why are unknown," Ulrich said. "For example, use of non-steroidal, anti-inflammatory drugs appears to lower risk of several types of cancer."
Knowing that CRP and SAA often are elevated among the overweight, the team investigated the effects of a yearlong exercise program on the levels of these biomarkers.
The study population consisted of 114 postmenopausal, overweight (body mass index greater than 24) and sedentary women, ages 50 to 75. About half of these were randomly assigned to a group that performed moderate physical activity 45 minutes per day, five days a week, for one year, while the other half participated in weekly stretching exercises. Researchers measured the concentrations of CRP and SAA in their blood at the beginning and the end of the test period.
A biologic mechanism
"Among obese women — those with a body mass index of 30 or higher-concentrations of CRP declined steadily over the course of the year by about 20 percent, and we saw a similar reduction for SAA," Ulrich said. "This effect of exercise on inflammatory markers may help to explain in part the associations observed between increased physical activity and reduced risk for cancer and other chronic disease. Our study suggests that a reduction in CRP and SAA is one of the possible biologic mechanisms by which exercise may reduce cancer risk."
Ulrich said that based on these findings, she and colleagues plan to conduct additional studies to evaluate whether levels of inflammation markers also influence cancer survival.
She added, "What is particularly interesting about the study is that obese women saw this benefit, even though they lost relatively little body weight. Another good reason to exercise!"
Current and former center co-investigators on the study include Drs. Anne McTiernan, Yutaka Yasui, Bess Sorensen, Melinda Irwin, Shelley Tworoger, Deborah Bowen and John Potter. Drs. Mark Wener and Brent Wood of the University of Washington were collaborators.