Fight Cancer With Good Old-Fashioned Exercise
Exercise is well-known as a way to protect against America’s top killer: heart disease. Now, physical activity is increasingly being studied as a possible weapon against the second most common cause of death: cancer.
Most experts agree that regular exercise can reduce the risk of colon cancer, and there is a growing consensus that it may also lower breast-cancer risk. For cancer patients, a burgeoning number of exercise programs are available, primarily to help relieve unpleasant side effects of the disease and its treatments. And there is some suggestion that physical activity may slow the course of the disease.
Two new studies, presented at last month’s annual meeting of the American College of Sports Medicine in Indianapolis, add to the mounting evidence that regular exercise may exert an “anti-cancer” effect. Both reports are from the Cooper Institute for Aerobics Research in Dallas, and both suggest that men with high fitness levels are less likely to die of cancer.
“We found that men who were classified as unfit (based on treadmill tests) were 80% more likely to die of cancer than fit men were,” says Carolyn Barlow, a biostatistician who examined the relationship of cardiovascular fitness, body mass index, or BMI, and cancer mortality in 22,703 men, ages 20 to 85, in a 10-year study.
Separately, a major study released last week underscored the importance of environment and lifestyle in preventing cancer. The study, published in the New England Journal of Medicine, suggested that, overall, genetic factors may account for 21% to 42% of cancer risk, with life factors accounting for the rest.
In Barlow’s study, men who were unfit and obese were at greatest risk, with a 2.6 times greater chance of dying of cancer than fit, normal-weight men. Excess body fat is known to increase risk for certain cancers--including colon, rectum, prostate, endometrium, kidney and breast (among post-menopausal women). The study, however, also revealed that low fitness--not fatness--was more predictive of cancer death: If a man was fit, being overweight did not raise his cancer risk.
“It is possible to be overweight and fit,” says Barlow, who notes that genetics play a strong role in a person’s body size and shape. “Our data suggest that low cardiovascular fitness may be viewed as a more important predictor of all-cancer mortality than increased BMI in men.”
The second study focused on the role a man’s fitness level plays in his risk of dying of lung cancer. The 25,883 male participants, ages 30 to 89, were members of the institute’s Aerobics Center Longitudinal Study--a group that didn’t smoke much, notes principal author Larry Gibbons. Just 18% were smokers and 37% were former smokers.
“But even with adjustments for age, smoking habit, alcohol intake and other potential risk factors, we found that the fitter a man was, the lower his risk of dying of lung cancer,” says Gibbons, who is medical director of the Cooper Clinic, the medical center affiliated with the institute. “Our research shows that if you’re a smoker, your risk of dying of lung cancer is cut in half if you are in the high-fit category.” If you’re a past smoker, he says, your risk is a third. If you’ve never smoked, your risk in the high-fit category is one-fourth.
This study is one of three to examine the link between physical activity and lung cancer, Gibbons notes. “Our findings suggest that fitness may protect the lungs against the ravages of cigarette smoke,” he says. They also suggest that “a sedentary lifestyle may be one of the factors contributing to the development of lung cancer.”
While the mechanisms by which exercise appears to protect against cancer aren’t known, current theories point to physical activity’s effect on the immune system, the nervous system and the endocrine system. “Stress plays a role in many diseases, including cancer, and physical activity helps relieve stress,” Gibbons says. “There is also some evidence that moderate physical activity prevents the formation of free radicals that can damage DNA and be a precursor to cancer.”
Theories differ for the various types of cancer, notes Rachel Ballard-Barbash, a physician specializing in nutrition, preventive medicine and epidemiology at the National Cancer Institute in Bethesda, Md. For example, she says, one reason regular exercise is believed to reduce the risk of colon cancer by 50% is activity’s role in speeding food through the bowel, which shortens the time carcinogens in fecal matter spend in contact with cells that line the colon.
“For breast cancer, theories point to exercise’s effect on hormonal metabolism and production,” Ballard-Barbash notes. “Among elite women athletes, there is evidence that regular physical activity leads to longer periods between ovulation and lowers levels of endogenous, or naturally occurring, estrogen, which may lower cancer risk.” There’s also some evidence that physical activity delays the age of a menarche, she says, a factor associated with reduced breast-cancer risk.
Scientists do not yet know a specific exercise prescription to reduce cancer risk. “For breast cancer it may be important to encourage physical activity in young girls,” she says. For cancer related to body fat, the exercise recommendation would likely be similar to one for weight loss and maintenance.
The American Cancer Society urges people to follow the U.S. surgeon general’s advice to accumulate 30 minutes of moderate physical activity most days of the week.
For more information: the American Cancer Society, (800) ACS-2345 or https://www.cancer.org; the National Cancer Institute, (800) 4-CANCER or https://www.nci.nih.gov.
