What's the level of evidence that exercise lowers breast cancer risk?
Much of cancer research on lifestyle is based on observational research, making it tough to replicate and prove cause and effect. But the exception is exercise: Here the evidence is strong for lowering breast cancer risk at every age in life, as well as endometrial cancer. Strong evidence is defined as good quality research leading to a recommendation, and will not likely change in the future.
The recommendation for exercise is one of the core recommendations to reduce cancer risk from the World Cancer Research Fund and the American Institute for Cancer Research. This advice is defined further that being active reduces the risk of postmenopausal breast cancer, while vigorous activity (defined as fast cycling and running) decreases both pre and postmenopausal breast cancer.
A mix of physical activity has consistently been recommended for overall health, and this year's Physical Activity Guidelines for Americans, abandoned the requirement for exercise bouts of at least 10 minutes, and simply says "Some physical activity is better than none." The federal government's 2nd Edition recognizes benefits for brain health, more cancer types, long term benefits for all ages from sleep to functioning, and chronic conditions such as diabetes; and also outlines the risk of not being active. The guidelines note that health benefits start right away, even from short episodes of activity.
What's new recently is the updated global scientific consensus that patients with cancer and survivors should be encouraged to remain active to improve common cancer-related health outcomes. Exercise not only reduces risk of breast cancer and recurrence, but improves survival for many types of cancers. Hundreds of studies encompassing millions of people diagnosed with cancer, points to a range of 10-20% risk reductions with higher rather than low activity levels. This reduction in risk was significant for breast cancer in women, whether premenopausal and postmenopausal.
How much activity was seen for risk reduction of breast cancer? The research measures metabolic equivalents—METs—for levels of activity. For breast cancer, a 25% lower cause of breast cancer mortality was found in approximately 10 MET hours per week. What do 10 MET hours look like? MET hours vary per person, but a general example is walking slowly 3.5 hours per week is equivalent to 10.5 MET hours. The more intense the exercise and expended energy used, the higher the MET per hour. But exercise at any level is beneficial.
The Physical Activity Guidelines for Americans recommends a mix of moderate and vigorous-intensity aerobic activity throughout the week. Specifically: 150 minutes of moderate exercise; or 75 minutes of vigorous; and additional strength exercises for 2 or more days a week. A combination of these activities provide "substantial health benefits."
But for cancer survivors, the specific levels of three times a week moderate intensity, aerobic and/or resistance training point to reduced risk, improved survival, and better quality of life. The Consensus Statement from International Multidisciplinary Roundtable goes further. They emphasize activity is safe for cancer survivors, and every survivor should avoid being sedentary. The evidence shows the combination of aerobic, and resistance training may improve the following symptoms many survivors face:
Anxiety and depression (specifically with aerobic training or when combined with resistance training)
Physical functioning and quality of life
No risk of exacerbating upper extremity lymphedema
Osteoporosis and bone health
New research also shows resistance training improves lymphedema, a common symptom of breast cancer surgery, regardless of weight loss. But it's still uncertain whether exercise has an impact on peripheral neuropathy, cognitive functioning, and falls.
Despite American College of Sports Medicine's updated exercise guidance for cancer prevention and treatment, many survivors are not active on a regular basis. Clinicians are urged to assess and refer patients to exercise or outpatient rehabilitation. Only a small percentage of clinicians refer patients with cancer to exercise programming for varied reasons. The Moving Through Cancer initiative now offers a specific exercise prescription after assessing for safety. The prescription offers details about aerobic and strength training.
Another great resource are the patient handouts "Sit Less. Move More." with the tagline, "Start where you are. Use what you have. Do what you can," and "Being Active When You Have Cancer." Tips are offered for home, work, and during commuting, emphasizing to choose what works for you, and is fun:
Walk to the mailbox
Rake some leaves
Start a neighborhood walking group
Walk during lunchtime, or after dinner with the family
To get started, talk to your doctor to assess any activity limitations because of medications, surgeries or treatment. Then find out if your hospital or local wellness center has a structured cancer exercise program. Many local cancer support programs, such as Cancer Support Community, and WeSpark, offer free programs for all activity levels.
The Exercise is Medicine handout urges patients to "reduce your tush time." With all the advantages of activity—from activating your immune system, and filtering blood, to enabling you to function better and stronger throughout the day—that's good advice.