Last year, the Journal of American Medical Association (JAMA) Internal Medicine published a study investigating the relationship between leisure-time physical activity and the incidence of 26 different types of common cancers.
This study included 1.44 million people and observed that high leisure-time physical activity was associated with a reduced risk of 13 different types of cancer.
Interestingly, the association between physical activity and reduced cancer risk was, for the most part, independent of body weight. This means that the positive effect of exercise is not related to the number on a scale and reveals the presence of more involved mechanisms. Proposed mechanisms to explain how exercise could protect against cancer are extensive, and more research is certainly needed. Regardless of the mechanism, it is clear that elevated levels of physical activity is a valuable evidence-based strategy to reduce cancer risk.
While exercise is important for reducing the risk of cancer, what about those patients afflicted with cancer already? Is it possible that cancer survivors could benefit from exercise interventions?
Consider the psychological challenge cancer presents.
Population-based research has found that cancer survivors have a doubling of risk for psychological complications compared to people without cancer.
Importantly, exercise is able to counter this psychological challenge due to its pronounced positive effect on mental health. As a snapshot, exercise has been shown to reduce depression, suppress anxiety, reduce symptoms of ADHD, improve cognition in patients with Alzheimer’s and Parkinson’s disease, improve age-related cognitive decline, decrease symptoms of obsessive-compulsive disorder, reduce feelings of stress, and lower the burden of post traumatic stress disorder.
In fact, the Canadian Network for Mood and Anxiety Treatments (CANMAT) updated their 2016 Clinical Guidelines for the Management of Adults with Major Depressive Disorder to recommend exercise as “first-line monotherapy for mild to moderate major depressive disorder and as second-line adjunctive treatment for moderate to severe major depressive disorder.”
Moving into scientific studies, investigations of exercise interventions on cancer survivors have highlighted impressive positive effects of exercise.
In one such example, a study published earlier this month in the journal of Breast Cancer Research and Treatment investigated the effects of 16 weeks of exercise training on quality of life markers in 240 women undergoing chemotherapy treatment for breast cancer.
When compared to the control group, the exercise intervention group had lower cancer-related fatigue, improved emotional functioning, improved cognitive functioning, less of a decline in physical functioning, and lower pain scores. When examining total symptom burden (a combination score derived from 32 different symptoms), exercise training significantly reduced the burden of disease in women with breast cancer undergoing chemotherapy.
Chemotherapy can be difficult to adhere to and patients are less likely to complete their treatment regime if the side effects are excessively drastic. However, because exercise can mitigate the side effects of chemotherapy and improve quality of life, a patient may be more likely to complete their chemotherapy if exercise is included. Consequently, exercise interventions may improve disease prognosis via improving treatment adherence, in addition to the metabolic effects we don’t yet fully understand.
The fact that exercise has an almost universal positive effect across a myriad of diseases with varied etiologies is perplexing to say the least. But perhaps the “how” doesn’t matter. What matters is that it works, and a large percentage Western civilization would benefit from incorporating additional physical activity into their daily lives.
By Brennan Smith, PhD