Regular Exercise Helps Fight Cancer

American Institute for Cancer Research
Sunday, 1 February 2004

Protection Conferred Beyond Its Role in Weight Control

During National Cancer Prevention Month, experts want people to know just how important physical activity is in reducing the risk of cancer. Current research is discovering a variety of ways in which regular exercise can help prevent the onset of the disease.

"We've known for a long time that regular exercise helps prevent obesity, which is a significant risk factor for cancer. We are now discovering that exercise protects against cancer in ways that go beyond its ability to prevent excess weight," said Ritva Butrum, Ph.D., Senior Science Advisor for the American Institute for Cancer Research (AICR).

Research Finds Link

The link between physical activity and reduced cancer risk has been demonstrated repeatedly in large and convincing studies. During the past year alone, several major studies relating to this question have been reported in scientific journals.

In the American Journal of Epidemiology (2003; 158:214-224), a study of 2,000 men and women found that those who exercised vigorously (to the point of sweating and/or getting out of breath) have a 40 percent lower risk of rectal cancer than people who exercised less.

Those who exercised moderately also reduced their risk, but the men and women who exercised vigorously during the previous twenty years had the most protection from rectal cancer. The reduced risk was similar to that seen with colon cancer.

In a study of 74,000 postmenopausal women, reported in the Journal of the American Medical Association (2003; 290:1331-6), those who engaged in 1-1/4 to 2-1/2 hours of brisk walking per week, or its equivalent, had an 18 percent lower risk of breast cancer compared to inactive women. Researchers concluded that even less strenuous physical activity provides breast cancer protection.

In a third large study, this one a 34-year follow up of 10,000 Finnish teachers, reported in the International Journal of Cancer (2003; 107:268-270), physical education teachers had a 17 percent lower risk of breast cancer than did the less active language teachers. The lower risk was found in those under and over the age of 50, adding support to the belief that lifelong physical activity may reduce breast cancer risk.

Explaining the Link

Scientists offer several explanations for the effect of physical activity on cancer risk. In general, physical activity seems to improve the body's antioxidant defense systems and to strengthen other immune defenses as well.

Sluggish movement of food as well as extended exposure to bile acids in the digestive tract seem conducive to cancer. Exercise reduces risk of colon cancer by speeding the movement of food and decreasing the secretion of bile.

In recent years, however, scientists have focused particularly on how exercise produces cancer-protective changes in the body's hormonal environment. Many believe that people who are overweight or obese and inactive produce higher levels of hormones that spur cell division. Since cancer is a malfunction of cells during division, this kind of rapid cell division provides greater opportunity for initiation of the disease.

By reducing bodily fat stores, exercise helps to reduce the level of excess hormones circulating in the blood. In addition, scientists believe physical activity also regulates the output of hormones by endocrine cells.

Steps You Can Take

"Growing evidence suggests that physical activity is a primary means of preventing cancer," said Melanie Polk, R.D., AICR's Director of Nutrition Education. "This means that something as simple as moving a little more can help forestall one of the most frightening illnesses that confront us as we grow older."

How much exercise? AICR's expert panel report, Food, Nutrition and the Prevention of Cancer: a global perspective, recommends one hour per day of moderate activity and one hour a week of strenuous activity.

"As you try to fit more physical activity into your schedule, take that recommendation as an ultimate goal. But start by doing a little more each week. Inactivity raises your risk of cancer, but every little bit of added activity can be protective," said Polk.

For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org

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