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RELATION BETWEEN PHYSICAL ACTIVITY AND CANCER RISK

Physical activity is defined as any movement that uses skeletal muscles and requires more energy than resting. Physical activity can include walking, running, dancing, biking, swimming, performing household chores, exercising, and engaging in sports activities.

A measure called the metabolic equivalent of task, or MET, is used to characterize the intensity of physical activity. One MET is the rate of energy expended by a person sitting at rest. Light-intensity activities expend less than 3 METs, moderate-intensity activities expend 3 to 6 METs, and vigorous activities expend 6 or more METs.

Sedentary behavior is any waking behavior characterized by an energy expenditure of 1.5 or fewer METs while sitting, reclining, or lying down. Examples of sedentary behaviors include most office work, driving a vehicle, and sitting while watching television.

A person can be physically active and yet spend a substantial amount of time being sedentary.

There is strong evidence that higher levels of physical activity are linked to lower risk of several types of cancer.

    • Colon cancer: In a 2016 meta-analysis of 126 studies, individuals who engaged in the highest level of physical activity had a 19% lower risk of colon cancer than those who were the least physically active.
    • Esophageal cancer: A 2014 meta-analysis of nine cohort and 15 case–control studies found that the individuals who were most physically active had a 21% lower risk of esophageal adenocarcinoma than those who were least physically active.
    • Stomach (gastric) cancer:A 2016 meta-analysis of 10 cohort studies and 12 case–control studies reported that individuals who were the most physically active had a 19% lower risk of stomach cancer than those who were least active.

For several other cancers, there is more limited evidence of an association. These include cancers of the pancreas,liver, and rectum.

Exercise has many biological effects on the body, some of which have been proposed to explain associations with specific cancers. These include:

    • Lowering the levels of sex hormones, such as estrogen, and growth factorsthat have been associated with cancer development and progression [breast, colon]
    • Preventing high blood levels of insulin, which has been linked to cancer development and progression [breast, colon]
    • Reducing inflammation
    • Improving immune systemfunction
    • Altering the metabolismof bile acids, decreasing exposure of the gastrointestinal tract to these suspected carcinogens [colon]
    • Reducing the time it takes for food to travel through the digestive system, which decreases gastrointestinal tract exposure to possible carcinogens [colon]
    • Helping to prevent obesity, which is a risk factor for many cancers

 

Relationship between being sedentary and the risk of cancer?

Although there are fewer studies of sedentary behavior and cancer risk than of physical activity and cancer risk, sedentary behavior—sitting, reclining, or lying down for extended periods of time (other than sleeping)—is a risk factor for developing many chronic conditions and premature death. It may also be associated with increased risk for certain cancers.

 

How much physical activity is recommended?

The U.S. Department of Health and Human Services Physical Activity Guidelines for Americans (2018) recommends that, for substantial health benefits and to reduce the risk of chronic diseases, including cancer, adults engage in

    • 150 to 300 minutes of moderate-intensity aerobicactivity, 75 to 100 minutes of vigorous aerobic activity, or an equivalent combination of each intensity each week. This physical activity can be done in episodes of any length.
    • muscle-strengthening activities at least 2 days a week
    • balance training, in addition to aerobic and muscle-strengthening activity

 

Is physical activity beneficial for cancer survivors?

Yes. A report of the 2018 American College of Sports Medicine International Multidisciplinary Roundtable on Physical Activity and Cancer Prevention and Control concluded that exercise training and testing are generally safe for cancer survivors and that every survivor should maintain some level of physical activity.

    • strong evidence that moderate-intensity aerobictraining and/or resistance exercise during and after cancer treatment can reduce anxiety, depressive symptoms, and fatigue and improve health-related quality of life and physical function
    • some evidence that exercise is beneficial for bone health and sleep quality
    • insufficient evidence that physical activity can help prevent cardiotoxicityor chemotherapy-induced peripheral neuropathy or improve cognitive function, falls, nausea, pain, sexual function, or treatment tolerance

In addition, studies have shown a possibility that physical activity may have beneficial effects on survival for patients with breast, colorectal, and prostate cancers.