Looking for a way to sidestep cancer? Try adding a few brisk walks and stair climbs to those side steps.
A new study involving nearly 1.5 million participants has found that exercise — or as the researchers call it, a higher level of “leisure-time physical activity” — is associated with lower risk in a substantial number of cancers, bolstering previous evidence of exercise’s role in cancer risk reduction. The findings, published today in JAMA Internal Medicine, further indicate exercise can reduce the risk of cancer despite body size or smoking history. In other words, even if you’re overweight and a smoker, you can still cut down your cancer risk if you get up and move.
“Size matters in epidemiologic studies because it gives you greater power to detect associations and to examine effects in subgroups,” said Dr. Anne McTiernan, a cancer prevention researcher at Fred Hutchinson Cancer Research Center. This study, she said, “was huuuuuge.”
Led by researchers at the National Cancer Institute, the epidemiological study cobbled together a dozen large U.S. and European prospective cohorts (groups of study participants who’d been followed for a number of years) in order to create a mega-pool of 1.44 million men and women. They then analyzed the participants’ information — their age, gender, body mass index, smoking status, self-reported data on exercise and, if applicable, cancer diagnoses — to determine the effect exercise had on various cancers. All told, 186,932 primary cancers were diagnosed during the follow up period (median follow-up was 11 years).
The evidence was significant. Exercise, already known to reduce the risk of heart disease and colon, breast and endometrial cancers, substantially lowered cancer risk in 13 of the 26 cancers examined, many by more than 20 percent.
And the benefit was much higher than that in some cases.
The risk of esophageal adenocarcinoma dropped by a whopping 42 percent in people who were active, and exercise cut the risk of liver and lung cancer by 27 and 26 percent, respectively. Working out also led to a 23 percent reduced risk for kidney cancer and a 22 percent reduced risk for gastric cardia (a type of stomach cancer).
Other cancer risks dropped as follows: endometrial by 21 percent; myeloid leukemia by 20 percent; myeloma by 17 percent; colon by 16 percent; head and neck by 15 percent; rectal by 13 percent; bladder by 13 percent and breast by 10 percent.
Conversely, exercise increased the risk of malignant melanoma by 27 percent, although researchers believed this was due to increased sun exposure since this association was most often found in areas with high ultraviolet radiation from the sun.
Exercise was also associated with a 5 percent bump in early stage prostate cancer but researchers chalked this up to the fact that physically active men are more likely to see a doctor and get screened than inactive men. The 5 percent rise, they concluded, was most likely “screening bias,” since there was no observed bump in advanced prostate cancers among active men.
Despite mountains of evidence showing the benefits of exercise, half the population of the U.S. does not meet the recommended physical activity levels (worldwide, the physical inactivity level is 31 percent).
According to the U.S. Surgeon General’s guidelines, for “substantial health benefits,” adults should do at least 150 minutes a week of moderate-intensity aerobic physical activity, with the exercise spread throughout the week rather than performed in one massive workout session. The guidelines also recommend strength-training that’s “moderate or high intensity and involves all major muscle groups” two days a week.
“The aerobics can be brisk walking,” McTiernan said. “[There’s] no need to become an athlete.”
But keep in mind: the more you exercise, the greater the health benefits. According to the U.S. guidelines, if you want more extensive health benefits, shoot for five hours a week of moderate-intensity exercise (or 150 minutes of vigorous-intensity aerobic activity).
McTiernan, who has conducted numerous studies on exercise as it relates to cancer prevention and survivorship, called the NCI study well-designed and well-conducted, and said the data used was from “very, well-respected cohort studies,” including the American Cancer Society’s Cancer Prevention Study; the Swedish Cancer Society and NCI’s Women’s Lifestyle and Health Study; and the Women’s Health Study and Physicians’ Health Study at Brigham and Women’s Hospital and Harvard Medical School.
There were some drawbacks, however. Although participants were fairly evenly split gender-wise, most of the participants were white, providing little information on the cancer-busting benefits of exercise in minorities. Information on the type of exercise was also limited, McTiernan said, with most of the activity recorded being aerobic (think running, walking, jogging or biking).
“It gives no information on associations with strength training,” she said. “Based on these findings, we can’t say what exercise and how much.”
She also noted the participants’ physical activity was all self-reported, which could be problematic since researchers have discovered that “people over-report their level of activity.”
Despite the drawbacks, McTiernan was enthusiastic about the findings and their public health implications.
“I'd say it's one more reason to stay active,” she said. “It's not a guarantee but it's probably going to reduce risk for several cancers.”
And considering the bump in malignant melanoma, she added this advice: “Those who choose to exercise outdoors, which I highly recommend, need to use sun protection to avoid the adverse effect of sun on melanoma and other skin cancers.”
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Diane Mapes is a staff writer at Fred Hutchinson Cancer Research Center. She has written extensively about health issues for NBC News, TODAY, CNN, MSN, Seattle Magazine and other publications. A breast cancer survivor, she also writes the breast cancer blog doublewhammied.com. Reach her at firstname.lastname@example.org.