Everybody knows that aerobic exercise builds endurance and strengthens the heart, and that strength training builds muscles. But did you know that exercise can help ward off cancer?
Exercise programs won’t tell you explicitly how to reduce your risk of cancer, but “physical activity is central to reducing your risk” says physician Michael Thun, vice president emeritus for epidemiology and surveillance at the American Cancer Society.
“There are two ways that regular exercise can potentially do that,” he explains. It can indirectly lower your risk by keeping off excess weight, or it can work directly on cancer risk.”
How to reduce your risk of cancer with regular activity
“With respect to colon cancer, the direct effect is very well documented. Studies show that even light to moderate regular activity is associated with lower risk compared with inactivity.”
Researchers at the Washington University School of Medicine in St. Louis reviewed 52 studies of exercise and colon cancer. The most active people were about 21 percent less likely to be diagnosed than their least active counterparts.
Researchers aren’t sure how to reduce your risk of cancer with activity that may protect the colon, even though the results are documented. “Bowel motility is one possible mechanism,” says Thun. “Just moving things through the bowel is better than having them sit there.” But, he cautions, “it’s much easier to propose mechanisms than to prove them.”
How to reduce your risk of cancer through more vigorous exercise
In contrast, it may take more than brisk walking or other moderate activity to lower the risk of breast cancer. “With colon cancer, just not being sedentary is a good thing,” says Thun. “With breast cancer, there’s fairly consistent evidence that the reduced risk occurs only with greater, moderate-to-vigorous activity.”
And it may never be too late to start.
Researchers tracked some 119,000 women in their 50s and 60s for seven years in the NIH-AARP Diet and Health Study. Those who reported more than an hour a day of moderate-to-vigorous activity—even if they hadn’t exercised earlier in their lives—were 16 percent less likely to be diagnosed with breast cancer than those who rarely did moderate-to-vigorous exercise.
“It looks like women who are more aerobically fit are less likely to die of breast cancer,” says Steven Blair, an exercise epidemiologist at the University of South Carolina.
Again, researchers aren’t sure why. One possibility: “Physical activity reduces the exposure of tissues to insulin-like growth factor,” notes Thun. If IGF promotes cancer, having less available in the bloodstream may help.
Exercise may also indirectly prevent cancer by keeping the pounds off. While “the direct effects of exercise are most clearly on large bowel and breast cancer,” says Thun, the impact of weight gain is broader.
“Weight gain is associated with quite a few cancers, notably postmenopausal breast cancer, colorectal cancer, endometrial cancer, pancreatic cancer, and adenocarcinoma of the lower esophagus,” he notes.
“And the list isn’t complete yet because there is accumulating evidence that obesity is a risk factor for several of the blood-forming cancers like leukemia and lymphoma.”
That’s why the American Cancer Society recommends that adults get at least 150 minutes of moderate intensity or 75 minutes of vigorous intensity activity each week (or a combination of these), preferably spread throughout the week.
Even without a direct answer to the question of how to reduce your risk of cancer, exercise is clearly a key.
“Just how much exercise is enough and how large is the benefit are still gray areas,” says Thun. “But the overwhelming reality is that most Americans are too sedentary, and the issue is not what the perfect amount is, but how we can all increase the amount we’re getting.”
Sources: Br. J. Cancer 100: 611, 2009. BMC Cancer 9: 349, 2009. CA 56: 249, 2006.