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Physical activity and cancer: A unique liaison

Move more … sit less

Karen Miller
Physical activity and cancer: A unique liaison
PHOTO: THINKSTOCK/STOCKBYTE

The link between physical activity and cardiovascular disease is well known. People who are more active have a lower risk of heart disease, stroke and diabetes, to name a few disorders. These three conditions alone account for almost 858,000 deaths a year, and rank as the first, fifth and seventh leading causes of death in this country.

PHOTO: THINKSTOCK/PURESTOCK

PHOTO: THINKSTOCK/PURESTOCK

Less well known and understood, however, is that the same physical activity can lower the risk of cancer as well. Several previous studies have documented the association between physical activity and a lower risk for breast, uterine and colon cancers.

The big news, though, is that more recent research by the National Cancer Institute and the American Cancer Society found that high levels of leisure-time physical activity were associated with lower risk of 10 additional cancers. Even better news is that seven of all the cancers studied had a greater than 20 percent reduction in risk: kidney, liver, esophagus, lung, stomach, uterine and myeloid leukemia, a cancer of the blood and bone marrow.

What is striking about this research is that the findings were evident across the board regardless of body size or smoking history.

Guidelines for Physical Activity

The 2008 Physical Activity Guidelines for Americans were clear. To maintain or increase overall health, adults should engage in 150 minutes a week of moderate-intensity activities, such as walking or dancing. For a greater challenge, individuals can up the ante to 75 minutes a week of vigorous-intensity activities, such as running or jogging.

Unfortunately, not many people got the memo. In a recent review by the Centers for Disease Control and Prevention, only 23 percent of adults in this country followed the guidelines. Apparently, sitting is preferable.

A recent release from the U.S. Bureau of Labor Statistics found that people spend almost three hours a day watching television and a scant 18 minutes in sports, exercise and recreation. And that’s for leisure time. It does not include commuting or computer use at work. So endemic is the problem that the World Health Organization has now identified physical inactivity as the fourth leading cause of death worldwide.

Link to Cancer

But what’s the connection behind physical activity and cancer? Apparently, a great deal, according to the National Cancer Institute. It has several biological effects on the body, the most noted of which is obesity. Physical activity helps prevent obesity and its harmful effects. Overweight and obesity are associated with at least 13 different types of cancer, which constitute 40 percent of all cancers diagnosed.

It lowers the levels of certain hormones, particularly insulin and estrogen. These hormones are essential for normal body functions but have a down side as well. Estrogen is important for sexual and reproductive development in females but in excessive amounts is linked to breast cancer, particularly in post-menopausal women. Likewise, insulin, which helps guide sugar into the cells for energy, can encourage the development and growth progression of cancer cells.

Physical activity also reduces the amount of time it takes for food to travel through the digestive system, thereby limiting exposure to possible carcinogens. This in turn can decrease the risk of colon cancer. It is also thought to aid in reducing inflammation and strengthening the immune system.

But here’s a bonus benefit. Regular physical activity may help reduce the risk of the recurrence of cancer. Circulating tumor cells are cancer cells that break off from a primary tumor and travel through the blood stream. They can result in metastasis, or spread of the tumor. If any of these cells remain in the body following surgery or chemotherapy, it can significantly increase the risk that the cancer will return.

In a small pilot study of patients who had been treated for colon cancer, researchers at Dana-Farber Cancer Institute discovered that those who engaged in both low and high levels of exercise had lower numbers of circulating tumor cells in their blood in comparison to patients who were
less active.

Get going

Although it is clear that physical activity is integral to one’s overall good health, the fact of the matter is that very few adults follow the recommended guidelines. The biggest challenge is getting started.

So, here’s a relatively simple solution. Take a walk. It’s easy; it’s free. It requires only a good pair of sneakers. But how do you figure out your intensity? Researchers at the University of Massachusetts found a simple way. Just count your steps per minute. Generally, 100 steps per minute meet the guidelines for moderate-intensity guidelines. Up the cadence to 130 steps per minute, and you’ve entered the vigorous-intensity zone. An easy way is to count your steps for 15 seconds and multiply by four.

If for some reason you cannot walk outside or in a gym, marching or walking in place in the comfort of your home is fine. It’s not the distance travelled that counts. It’s the movement. Instead of sitting through mind-numbing commercials, get up and march.

The results might surprise you. As the American Cancer Society noted in a recent study, “Even a little walking may help you live longer.”

How much of what?

According to the PhysicalActivity Guidelines for Americans:

  • 150 minutes each week of moderate-intensity aerobic activity

             OR

  • 75 minutes each week of vigorous-intensity aerobic activity

             OR

  • An equivalent combination of both

            AND

  • Muscle strengthening activities two or more days a week

 

Examples of moderate-intensity activities

  • Walking (3 miles per hour or faster)
  • Bicycling (slower than 10 miles per hour)
  • General gardening
  • Dancing
  • Light house cleaning

 

Examples of vigorous-intensity activities

  • Jogging, running, race walking
  • Swimming laps
  • Jumping rope
  • Bicycling 10 miles per hour or faster
  • Most competitive sports

 

Can you sing?

There is often a fine line between moderate-intensity and vigorous-intensity activities. With a little bit more effort, you can move from one to another, and not even realize it. But how do you know which is which?

Try the talk test. In moderate activities you can comfortably chat, but you can’t sing any more than a few words without running out of breath. In vigorous activities, you can’t say any more than a few words without having to pause to breathe.

 

www.dana-farber.org/community

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