Exercise and Cancer Prevention - Cancer

Exercise and Cancer Prevention

Several studies among men and women have indicated that those who are physically fit or physically active have lower death rates from cancer. In the October 1993 issue of American Health , Michele Wolf reports a study of more than 10,000 men and 3,000 women examined at the Institute for Aerobics Research in Dallas. She found that those deemed most fit on a treadmill test had much lower cancer death rates in the ensuing eight years. There was a four-fold difference in cancer deaths among the men and a sixteen-fold difference among the women. The strongest evidence for exercise's protective effect involves colon cancer, a leading cause of cancer deaths among Americans.

Wolf goes on to report that exercise for women, particularly during teenage and young adult years, seems to be associated with lower rates of breast cancer and various hormone-related cancers of the reproductive tract. Dr. Rose Frisch of the Harvard School of Public Health found that among nearly 45,400 female college alumnae, those who had been college athletes or who trained regularly had about half the risk of later developing breast cancer than nonathletes. Nonathletes also had higher rates of cancers of the uterus, ovary, cervix, and vagina.

The main benefit of exercise in reducing cancer risk in women is believed to be a lower lifetime exposure to estrogen, which can stimulate growth of cells in the breasts and reproductive organs. Physical activity can change the hormone ratio and reduce body fat, which itself increases the amount of cancer-stimulating estrogens in the blood. Since one-third of a woman's estrogen before menopause is produced by body fat, leaner, fitter women tend to manufacture less.

Wolf adds that exercise may also help fight other forms of cancer because of its ability to boost the performance of two types of immune system cells–natural killer (NK) cells and macrophages. Although NK cells and macrophages seem to inhibit tumor growth, exercise cannot eliminate it once it begins to spread. It may, however, prevent malignant cells from spreading. Exercise physiologists have not yet determined exactly how much exercise is needed to lower the risk of cancer.

Exercise helps decrease body fat and increase lean body mass, a process that may foster a more favorable hormone balance in early breast cancer–and perhaps other hormonally sensitive cancers as well. Several studies have also suggested that exercise helps overcome cancer cachexia, the condition by which people suffer debilitating weight loss and strength, even when they eat an adequate amount of food. Exercise may improve the body's conversion of glucose to useful energy and make it more sensitive to insulin.

According to Simone, the main benefit of exercise for cancer patients is that, in most cases, it produces a higher number of white blood cells, specifically granulocytes, that are needed to fight off infections and tumors. He states that people who exercise tend to have higher B and T killer cell counts. During exercise a person's temperature rises slightly, a condition accompanied by the production of pyrogen, an important protein produced by white blood cells that enhances lymphocyte functions. Elevated temperatures can also kill viruses–and have also been shown to kill cancer cells.

Role of Exercise in Colon, Breast, and Lung Cancer.     A Stanford study conducted by Dr. Ralph Paffenbarger found that moderately active men are 50% less likely to develop colon cancer than less active men. Exercises must be aerobic, strengthen the immune system, decrease harmful effects of stress-related hormones, and burn 1,000 calories a week. Exercises must also be monitored along with diet, as several studies show that exercise combined with a high-fat diet may accelerate tumor growth. Another study at Harvard University found that women active in swimming, running, gymnastics, and volleyball had significantly less risk of developing cancer of the breast, uterus, ovaries, cervix, and vagina. The study also discusses exercises that have proven helpful for patients undergoing surgery, chemotherapy, radiation, or biological therapy.

Exercise during Chemotherapy.     Chemotherapy suppresses the immune system and can cause loss of energy and appetite, nausea, vomiting, or mouth sores. Cancer specialists usually advise intravenous chemotherapy patients to avoid exercise for 24 hours following therapy because heart irregularities are more frequent during this time. According to Nixon, several studies have shown that aerobic exercise 24 hours after treatment increases appetite, increases the body's ability to utilize food nutrients, and decreases nausea.

Stationary Bicycle.     In Living with Exercise , Dr. Steven Blair suggests that people at risk for cancer must burn at least 1,000 calories per week to prevent tumors. He notes that chemotherapy patients in several clinical trials were able to increase their basal metabolic rate (BMR) 4–6% while using stationary bikes, as well as increasing their energy levels and appetite. Dr. Mary Winningham of the University of Utah College of Nursing found that aerobic stationary bicycling helps cancer patients regain stamina, appetite, and muscle strength.