The Physical Benefits of Exercise in Cancer Prevention

Cancer, the nation-wide’s next leading killer, is not only one illness. Exercise has clear benefit against some major malignancies and possible advantage against others, but it offers no defense against many cancers. About 1,373,000 Americans will be diagnosed with cancer every year, and some 570,000 will die from the disease. Physically active individuals have a lower overall risk of cancer than their sedentary peers. In part, this may be explained by the fact that active people tend to have healthy lifestyles; eating well, avoiding tobacco and excess alcohol, and getting regular preventive checkups all help fight cancer. But there are also biological explanations for the benefits of exercise.

Most important, exercise reduces body fat, and obesity is a major contributor to many malignancies. Exercise also appears to reduce the body's production of various growth factors, proteins that may promote the multiplication of malignant cells. Physical activity also lowers levels of insulin, another potential growth promoter. Other hormonal effects help explain how exercise reduces the risk of breast cancer and how it may protect against certain reproductive tract malignancies. Other possibilities include potential antioxidant and immune-enhancing properties of exercise, but these remain speculative.

The evidence is best for colon cancer. More than fifty studies from around the world show that physically active people are less likely to develop colon cancer than inactive individuals. The protection is substantial, amounting to a 30 to 40 percent reduction in risk. And as in the case of heart disease, moderate exercise will confer excellent benefits.

Breast cancer is the other big target of physical activity. More than sixty studies suggest that women who exercise regularly can expect a 20 to 30 percent reduction in the chance of getting breast cancer. Considering that about 213,000 Americans will be diagnosed with breast cancer this year, that's a big benefit—and it applies about equally to pre- and postmenopausal women. And a 2005 Harvard study of 2,987 women with breast cancer linked moderate exercise, such as walking for twenty-five to forty-five minutes a day, to a substantial improvement in survival.

Exercise may help prevent breast cancer by reducing estrogen levels and/or decreasing tissue responsiveness to the female hormone. Moderate exercise will confer most of the benefit, but intensive exercise appears to add some additional protection. Like the breast, the female reproductive organs are estrogen-responsive, and several studies suggest that women who exercise may have a reduced risk of cancer of the uterus, but not the ovaries.

The prostate is also a hormone-responsive organ, but in this case, the driving force is testosterone, the major male sex hormone. Prostate cancer displays much more clinical variability than most other malignancies, and investigations of exercise and prostate cancer have produced widely varied results. Some suggest protection from modest exercise (such as walking), others indicate benefit only from very intense exercise, while still others cannot detect any link. More study is needed.

Incomplete evidence is also the watchword for lung cancer and pancreatic cancer, with several studies hinting that exercise can help. Lung cancer is common, pancreatic cancer uncommon—but since both are deadly, even a little protection would be welcome indeed. And although exercise may not prevent or treat other malignancies, cancer specialists have learned that appropriate levels of physical activity can help rehabilitate cancer patients, improving energy, self-confidence, and overall well-being.

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