- By Gayle Golden
Research has long shown that physical activity is an important part of living a long and healthy life by lowering the risk of certain diseases, including more common cancers. Now, a new study has gotten a lot more specific, linking moderate exercise with a lowered risk for getting 13 types of cancer, many of which occur later in life.
The reduced risk doesn’t come from Herculean workouts or lifelong training regimens. All that’s required is 150 minutes per week of, say, brisk, purposeful walking.
It also appears that the benefit applies to literally every body, from the thin to the overweight — a result suggesting that exercise might be an independent and powerful factor for cancer prevention.
“There’s certainly a lot of evidence to suggest that physical activity is among the most important things you can do to protect your health,” said Steven Moore, an investigator in the division of cancer epidemiology and genetics with the National Cancer Institute and the lead author of the study, published online in May by JAMA Internal Medicine.
Big Pools of Data
The study is part of a growing practice among epidemiologists of using huge data sets drawn from cooperative research ventures to reveal relationships that smaller studies usually can’t detect.
In this case, plenty of previous studies had shown that moderate-intensity physical activity reduced the risk of certain common cancers, such as breast, colon and endometrial. But the results were far less clear for other cancers that occur less frequently among smaller samples.
As the evidence continues to accumulate, there’s more and more incentive for people to become active.
— Steven Moore, National Cancer Institute investigator
“So we pooled as much data as we could get our hands on,” Moore said. Using the National Cancer Institute’s Cohort Consortium, the study tracked a sizable 1.44 million people from among 12 cohort studies in the United States and Europe, tracking the data for more than a decade. In that time, roughly 187,000 new cancers had occurred in the cohorts.
By applying sophisticated statistical analyses, the researchers compared those cancer diagnoses with how much exercise the participants reported doing during their leisure time. As expected, the results confirmed previous findings that the more common breast, colon and endometrial cancers occurred less often among those who did moderate-intensity exercise. But more intriguingly, the study also showed that same amount of exercise also significantly reduced the risk of developing cancers of the esophagus, liver, stomach, kidney, bone marrow, blood, head and neck, bladder and, for former or current smokers, lungs.
In all, those cancers account for 75 percent of all cancers in the United States and 61 percent worldwide. Most appear later in life.
Participants were a median age of 60 when the studies began and were followed for years, some to age 98.
“Most of these people are getting diagnosed with cancer in their late 60s or early 70s, which is actually the typical period of highest incidence for cancer,” Moore said.
More Is Not Always More
The more vigorous exercisers fared the best. Those who exercised most intensely were 20 percent less likely to get those 13 cancers than the most sedentary participants, the study reported.
Yet even moderate exercise made a difference. Overall, the cancer risk was lowered by doing just the minimum, 150 minutes per week of moderate aerobic exercise recommended by the U.S. Department of Health and Human Services.
And more is not always more when it comes to exercise benefits, Moore said. In another large cohort study published last year, he and others discovered that people who exercised the minimum amount per week reduced the risk of death by 31 percent over those who did no physical activity. The benefit rose to 39 percent for those who ramped it up to three or five times that minimum, which translates into walking seven hours, biking leisurely five hours or running a little more than two hours each week. Yet pushing it even harder gave no additional gain, the study found.
Nor does the latest cancer study suggest it takes a lifetime of exercise to get the benefit. When the researchers checked halfway through the cohort studies at five years, the reduced risk of cancer was as strong for exercisers at that point as it was after a decade.
“It doesn’t appear that you have to have been doing the physical activity your whole life to get that benefit,” Moore said, although adding that more long-range studies are needed to nail down that suggestion.
In a more sobering finding, the study showed that exercise actually increased risk for malignant melanoma as well as non-advanced prostate cancer. That’s likely because exercisers spend more time outdoors in skin-damaging sunlight and also tend to get more frequent checkups, often prompting an early diagnosis of prostate cancer.
Every Body Wins?
The possible reasons for the lowered cancer risk aren’t clear. The researchers suspect that exercise affects three metabolic pathways influencing cancer development: sex steroids, such as estrogens and androgens; insulins and related growth factors and proteins involved with inflammation.
Intriguingly, though, the reduced cancer risk held true in this study even for those with a high body mass index, which is itself a risk factor for certain cancers. When the researchers looked only at the overweight or obese participants, they discovered risk was lower for 10 of the 13 cancers.
Anne McTiernan, a physician and cancer researcher with the Fred Hutchison Cancer Research Center in Seattle, called that result “somewhat reassuring,” but said it requires more direct study before being deemed true. The problem, she said, is that the studies relied on self-reported physical activity.
“We know that especially in this country, people who are overweight and obese tend to overreport how much physical activity they do, and they tend to underreport how much they eat. So those types of variables can be difficult to tease apart,” said McTiernan.
She says it is true, however, that direct studies — such as those using blood tests to measure the effects of exercise and diet on sedentary people — confirm that moderate exercise lowers estrogen levels in post-menopausal women and insulin levels for men and women. (Both estrogen and insulin have been linked to higher risk for some cancers.)
“We just see an even bigger effect if we get them to lose weight,” she said.
Both research tacks are useful, of course, and Moore says the next challenge for the large-cohort studies will be to figure out how varying intensities of exercise relate to specific cancer risks. Ultimately, he said, the goal of all this research is to get people moving.
“As the evidence continues to accumulate,” he said, “there’s more and more incentive for people to become active.”
Looking to get moving but not sure how? One of the biggest challenges is overcoming fear, said McTiernan, who studies the effects of exercise on sedentary people.
“If people have no experience with exercise ever, they may be afraid to start,” she said. “Someone who has very bad arthritis might fear they’re going to get worse with exercise, although studies show they actually do better.”
Here are a few tips for success:
- Identify what you love to do. People over age 50 are a varied group, who may be caring for grandchildren, raising teens, leading busy work lives or facing health problems of their own or of a loved one. Exercise needs to work within those demands and with your preferences, whether it’s running, biking, swimming or just walking. “We always say the best exercise is the one you’re going to do successfully and do consistently,” McTiernan said.
- Sneak it into your everyday life. Exercising doesn’t always mean suiting up and hitting the gym. At work, take the stairs instead of the elevator. If shopping, park farther away from the store so you can briskly walk to the door of your destination. If you have teenagers or grandchildren who play sports, don’t just sit and observe; walk around the field.
- Commit to a schedule. It’s best to set a specific time you’ll devote to the exercise versus figuring you’ll get to it at some point. Evaluate the best time for your energy level. If you don’t schedule it, McTiernan said, “you end up stopping at the end of the day and you’ve not done anything.”
- Start slowly, because it doesn’t take much. The minimum recommendations of 150 minutes per week means just about 30 minutes per day of moderate-intensity exercise if you do it five days a week. If it seems like too much, start with 10 minutes to keep it from overwhelming you. And don’t think you have to be an athlete. Start with a brisk walk and build from there.
- Get advice from your physician. In general, exercise relieves pain from physical maladies, such as arthritis. But if pain keeps you back, talk to your health care provider to get enough relief to exercise or for any other conditions you need to monitor. And look for alternatives to pounding the pavement, such as stationary bikes. “That way, you can still move those joints without putting a lot of weight on them,” said McTiernan.