May 29, 2023

Rob Newton’s father liked to take long walks before he was diagnosed with prostate cancer in 1993. But he gave them up after his doctors told him to take it easy. His son thought this was a terrible idea.
“I watched him experience overwhelming fatigue and a decline in muscle mass and fitness,” Newton recalls. “I tried to get him to exercise, but his doctors told him to rest.”
Newton, now a professor of exercise medicine at Edith Cowan University in Australia, is convinced that regular exercise after cancer surgery and during radiation therapy would have prolonged his father’s life. He died — of a stroke — three years later.
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“The doctors’ advice killed him due to the rapid onset of vascular disease caused by his sedentary lifestyle,” Newton says. Motivated by his father’s experience, Newton now studies the relationship between exercise and prostate cancer.
“Much of what was happening to my dad was the deconditioning and failure of his body systems due to his lack of movement,” Newton says. “His body was trying to fight the disease and the toxicities of his treatment, but we were not giving it the environment to succeed. I know that if I could have got him exercising each day he would have lived longer and not struggled as much.”
Today, many in the medical world agree. Ideas about exercise and how it affects cancer, and patients being treated for and recovering from the disease, have undergone remarkable changes in the years since Newton’s father succumbed.
A growing amount of epidemiological literature indicates that exercise lowers cancer risk, controls disease progression, and enhances physical functioning and psychosocial outcome. Evidence not only supports the positive effects of exercise before, during and after cancer therapy but also suggests that regular exercise over time actually reduces the risk of even developing many cancers.
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Recent research in breast cancer patients also indicates that regular physical activity can improve cognitive function, as well.
“Today, exercise is so well accepted for its wide range of physical and mental health benefits that it is sometimes hard to fully appreciate the earlier days, when so many aspects were still unknown and we were working through the research methods,” says Graham Colditz, who has been studying the cancer-exercise connection for nearly three decades and led a groundbreaking 1999 study that showed women who engaged in seven or more hours of moderate or vigorous exercise weekly had nearly a 20 percent lower risk of developing breast cancer than those who reported exercising less than one hour a week.
“People have been making the link between physical activity and good health for centuries, but good evidence on its impact on specific diseases and longer life are relatively recent,” says Colditz, deputy director of the Institute for Public Health at Washington University in St. Louis.
By the 1980s, the links between regular physical activity and cardiovascular health “and the ability of physical activity to help add years to one’s life were being better understood,” Colditz adds. “For cancer, the research took a bit longer to emerge.”
Early studies initially focused on the connection between high physical activity jobs — letter carriers, for example — and colon cancer and “showed strong links between activity and a lower risk,” Colditz says.
Since then, “the field of exercise oncology has exploded,” says Elizabeth Salerno, an assistant professor of surgery at Washington University’s School of Medicine and a co-author of the cognition study. “We have found consistent and compelling evidence that physical activity plays an important role in cancer prevention and control.” These include bladder, breast, colon, endometrial, esophageal, renal and gastric cancers, according to a growing body of research.
Research is also starting to show it’s possible to quantify how much exercise may make a difference after a cancer diagnosis. “Studies show that 150 minutes of weekly exercise dramatically improves survival,” says Bente Klarlund Pedersen, clinical professor at the University of Copenhagen and head of its Centre of Inflammation and Metabolism. “It is becoming more and more evident that exercise can have more direct effects on cancer and its treatment.”
Experts, who have long touted the benefits of exercise on physical and mental health, are now starting to figure out why it works with cancer. Research shows that moderate to vigorous exercise prompts changes at a molecular level that can affect cancer development and growth, lessen the debilitating side effects of treatment and extend survival.
“This means for aerobic exercise, it has to pass the talk test — that is, you are breathing heavily and can only talk in short phrases,” Newton says. “If you can hold a conversation then the intensity is too low. For resistance training, it has to be a weight you can only lift six to 12 times. Any more and the weight is too light.”
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Research is also focusing on the effects of exercise on other aspects of the body that may play a role in allowing or preventing cancer, including immune function, hormones and other molecules produced during exercise that may suppress cancer cell growth, blood flow through tumors, inflammation inside the body and the balance of muscle and fat tissue, Newton says.
His team is interested in the effect of myokines, molecules produced by muscle cells in response to muscular contraction. Exercise increases myokines, which remain elevated even at rest. “When cancer cells are exposed to these myokines, their rate of growth and propensity for metastasis is greatly reduced,” Newton says of his findings.
Moreover, his research, and studies conducted by others, suggest a strong relationship between high fat mass and poorer survival in those with cancer, along with a positive connection between muscle mass and cancer survival, he says. “The take-home message is that people with cancer should maintain or preferably increase their muscle mass as a priority,” and prevent fat gain, he says.
Recent research led by Michelle Janelsins-Benton, who heads the Cancer Control & Psychoneuroimmunology Laboratory at the University of Rochester, found that exercise also can reduce the chances of cancer-related cognitive decline (CRCD), a finding scientists hope to study further. They want to examine how exercise influences CRCD, possibly through the production of certain chemicals necessary for brain health, for example, the brain-derived neurotrophic factor, a protein that increases with exercise.
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The researchers measured physical activity and cognitive function in breast cancer patients before, during and six months after therapy. Physical activity declined during chemotherapy, but recovered to pretreatment levels at six months, according to the study. Patients who engaged in more moderate to vigorous physical activity before and during treatment maintained better cognitive function than those who did not.
“Exercise oncology programs are growing across the country to promote survival and physical improvement for patients during treatment, but knowledge about the role of exercise in preventing cognitive decline is still emerging,” co-author Salerno says. “Hopefully, more trials will tell us whether exercise during chemotherapy can also change the course of this debilitating phenomenon.”
Animal studies — which don’t necessarily translate into humans — suggest that exercise also can provoke an immune system response that shrinks tumors. When Pernille Hojman was a senior researcher at the Center for Physical Activity Research, Rigshospitalet in Copenhagen, she conducted pivotal studies in mice linking exercise-induced immune system natural killer (NK) cells to tumor reduction.
“Mice with access to a running wheel demonstrated a reduction in tumor volume and incidence of at least 60 percent across several different tumor models,” says Pedersen, a co-author of the study. “[She] suspected that NK cells were involved in mediating the anti-cancer effect. She carefully studied the tumors from trained and untrained mice and found that tumors from the running mice had … five times more NK cells.”
While some newly diagnosed cancer patients might resist the advice to work out, experts are convinced that being fit for the onset of therapy will enhance resilience and help patients cope with the side effects of treatment. “It’s understandable if somebody just wants to pull the covers over their head and hide,” says Daniel Santa Mina, associate professor of exercise and cancer at the University of Toronto. “I always tell them that exercise is more important now than ever.”
The federal government’s guidelines recommend at least 150 minutes of aerobic activity every week, along with at least two sessions of muscle-strengthening resistance training for healthy adults as well as those with chronic conditions or disabilities, advising the latter to work out under the supervision of a health-care provider. This could vary, however, for some cancer patients undergoing treatment, experts say. For example, resistance training may be more valuable for those with muscle loss than aerobics, while aerobics might help patients also at heart disease risk.
Regardless, they agree it’s better to do something than nothing.
“Even if you just walk to the mailbox and back, or just take a single flight of stairs, any movement, however brief or light, is likely to have some benefits,” Salerno says. “It’s important to start somewhere.”


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