Cancer can be deadly. However, research is showing promising data on how physical activity helps the body and mind heal—and prevent—this disease. A paper published in the Journal of the American Medical Association (Moore et al. 2016) indicates that physical activity lowers the risk of 13 types of cancer.
There's more positive news about exercise and cancer. A report from the Memorial Sloan Kettering Cancer Center states, "Multiple studies show that regular physical activity is linked to increased life expectancy after a diagnosis of cancer, in many cases by decreasing the risk of cancer recurrence" (Grisham 2014). The American Cancer Society, World Cancer Research Fund, American Institute for Cancer Research, American College of Sports Medicine, and U.S. Department of Health and Human Services are just some of the organizations that advocate physical activity for cancer patients and survivors (Grisham 2014). Thus, it is not a question of whether exercise helps, but rather of how much works—based on dosage, quality, conditioning and cancer type.
There are three ways to look at battling cancer. For those who don't have it, lowering risk is the primary goal. For those who've had it, successfully recovering and of course reducing the chances of recurrence are of utmost importance. For those who currently have it, the priorities are getting rid of it and minimizing the harmful effects that both the disease and the treatment have on the body. Exercise has been shown to help with all three.
Cancer and Exercise Research: An Overview
Cancer is simply a collection of abnormal cells that are dividing without stopping; in other words, their growth is out of control. Most often (not always), the result is a tumor. Some tumors are benign and will stay localized, but cancerous tumors are malignant and may spread (metastasize) to other parts of the body.
The immune system houses the forces that keep cancer at bay. In fact, we have a potent inflammatory agent called tumor necrosis factor that can be friend or foe, depending on the situation (Wang & Lin 2008). When our immune system is strong, we battle cancer successfully. When immunity is not strong, or if the cancer is potent, we may lose the battle and develop noticeable symptoms of cancerous growth.
Taking an "active approach" to fighting cancer is indeed the best choice. In a 2005 Harvard study, breast cancer patients who exercised at moderate intensities 3–5 hours per week (high volume) lowered the odds of dying from cancer by about half, compared with sedentary patients (Holmes et al. 2005). Even a little exercise improved patients' odds, regardless of stage or diagnosis timing.
Studies have also shown that those who exercise early in life have a lower chance of breast cancer later in life. Chinese women who exercised an average of 70 minutes per week during their teens reduced their chances of dying from cancer by 16%, and those who kept exercising as adults had a 20% lower risk of premature death from all causes, compared with other women (Nechuta et al. 2015).
The amount of exercise to aim for, particularly during or just after dealing with a bout of cancer, is a delicate balance of getting enough to make a difference and not getting too much—an amount that could suppress immune function. The reason for this yin-yang relationship is linked to the endocrine system and the body's perception of exercise as stress.
Epinephrine—released during exercise—helps to circulate natural killer cells in tumors. The NK cells move into the bloodstream and infiltrate tumor cells, causing them to shrink. Researchers confirmed this theory using several different methods, including using mice with no NK cells, blocking epinephrine flow and injecting mice with epinephrine. All studies led to the same conclusion: Epinephrine caused NK cell infiltration (Neiman et al. 1995). Further studies found that it was Interleukin-6 (IL-6), a known inflammatory marker, that served as the immune cell signal. Only IL-6 sensitive NK cells showed this response, and IL-6 helped guide NK cells to the tumors.
Other hormonal effects of exercise include insulin reduction, an increase in insulin–like growth factor 1 (IGF–1) and a decrease in leptin levels (Dutta et al. 2012). When leptin levels are high, various cancers survive better, grow faster and spread more (Dutta et al. 2012). Additionally, leptin causes the release of inflammatory agents that can complicate cancer risk. Sex hormones, cortisol and prostaglandins are currently being researched for their roles in cancer progression and prevention. Exercise has also been shown to minimize the negative effects of conventional cancer therapy. A meta-analysis of 16 studies found that cancer patients who exercised had consistently better quality of life, compared with their nonexercising counterparts (McTiernan 2006). The benefits were both physical and mental and included less fatigue, more energy, fewer hospital stays and doctor visits, and higher self-esteem.
For more information, please see “Exercise & Cancer” in the online IDEA Library or in the November–December 2016 print edition of IDEA Fitness Journal. References are online only. If you cannot access the full article and would like to, please contact the IDEA Inspired Service Team at 800-999-4332, ext. 7.