Does Exercise Prevent Cancer?
The more physically active I am, the happier and healthier I feel. This is why I choose to exercise every day that I can. I just love to get outside, plug myself into a Podcast and get my lungs and muscles working. It makes me feel like I’m physically and mentally beating cancer. Of course, going through active treatment sometimes makes exercise difficult, but the days when I’m forced to succumb to the side effects are thankfully still very rare. On weeks like this when I’m two weeks past my latest chemo and the weather is so fantastic, I go a bit overboard (my Fitbit is telling me that I’m averaging 17,000 steps a day) but it feels awesome.
But is there any evidence that it does me any good?
Primary Cancer Prevention
Firstly let's look at the evidence that exercise protects the body from developing primary cancer. For ethical and practical reasons, studies that attempt to understand links between lifestyle factors and disease are generally observational and are therefore considered less statistically valid than randomised controlled experiments. The main drawback of observational research is that it is difficult (if not impossible) to establish cause and effect. For example, despite the huge number of studies showing that smokers are more likely to get lung cancer, the tobacco industry successfully rejected the causal effect for decades. They argued instead that it was a gene that caused people to both smoke and get lung cancer until such a point that the volume of evidence was overwhelming.
Despite the drawbacks of observational research, the sheer volume of studies that now link physical activity with the prevention of some forms of cancer is now so great that guidelines published by the NHS, The National Cancer Institute, Macmillan and global government backed organisations now recommend partaking in a moderate level of exercise to reduce the risk of developing cancer.
The evidence is most compelling for cancer of the colon, breast and endometrial cancer (cancer of the lining of the womb or uterus) where studies have shown a 25%, 24% and 23% risk reduction respectively. Scientists currently understand very little about the complex biological mechanisms that contribute to any protective effect but research on animal subjects has indicated the involvement of multiple pathways including those related to sex and metabolic hormones, inflammation and and the immune system.
It is likely that the level of protective effect will be dependent upon the characteristics of the cancer and the pathways it exploits, such that some people will benefit significantly from exercising whereas others will see little direct impact on their risk of developing cancer.
Protecting from a Recurrence
[a] brisk 30-minute walk a day ‘STOPS killer breast cancer returning'
So, is there any reason why people who have already had cancer should include regular exercise as part of their rehabilitation and treatment program? According to a recent headline in the Sun newspaper, the answer is a resounding YES. The headline, published earlier this year declared that “[a] brisk 30-minute walk a day ‘STOPS killer breast cancer returning’”. Really?
If you look beneath the headline, the data comes from a meta-analysis of 22 studies, six of which show an average 24% reduction in recurrence and a 34% reduction in breast-cancer related morbidity for those people that engaged in physical activity after primary diagnosis. Other studies that have looked at a combination of healthy eating and exercise have have shown that women who decreased physical activity after a breast cancer diagnosis were four times more likely to die than those who increased or maintained the same level of activity and women who engaged in moderate physical activity and ate the recommended 5-a-day portions of fruit and vegetables had a 50% reduction in mortality. Whilst these studies are certainly promising, their results are even more controversial than those in the primary setting as they are fewer in number and even more susceptible to difficulties establishing cause and effect. How can you establish that a lack of exercise caused cancer to return or progress? Indeed, it could well be the other way round - i.e. the physical stress the growing cancer has on the body could have prevented the person from being able to engage in physical exercise. Despite the headline from the sun, the jury is still out on whether exercise can help prevent a recurrence or offer any protection to those dealing with metastatic cancer.
Strength and Resilience
So why do I exercise?
Well, apart from it feeling fantastic, I'm convinced that it helps me physically. According to the Health, Eating, Activity, and Lifestyle (HEAL) study, breast cancer patients who undergo chemotherapy and radiotherapy decrease their physical activity by 50% after treatment. This doesn’t surprise me - it can be really difficult to have the physical strength and motivation to exercise when you’re suffering the side effects of cancer treatment, but in my opinion it is essential to incorporate exercise into your daily ritual to build the strength and resilience you will need to face the rigours of treatment.
Certain chemotherapy agents such as anthracyclines and other cancer treatments can be cardiotoxic. For example, my treatment regime includes the monoclonal antibody Herceptin. Though it has been a real game-changer for people with HER2-positive breast cancer (increasing median survival for metastatic patients by 24%), it can affect the heart’s ability to pump blood and on rare occasions it can cause heart failure. My heart function is therefore tested regularly using a MUGA scan. If the results were too far out of the normal range my oncologist would have to stop prescribing Herceptin and I would lose out on it’s proven survival advantage. Strengthening the heart through regular exercise can play a key role combatting the effect that Herceptin may be having on my heart allowing me to keep taking the drug which ultimately improves my prognosis.
Exercise can also play a key role in minimising other treatment side effects such as changes in body composition (i.e. decreased muscle mass and increased fat distribution), fatigue and anxiety. These symptoms can have a major impact on quality of life, increase the chance of developing secondary cancers and affect the mind and body’s resilience for withstanding further life-saving treatments.
It is widely accepted that physical exercise can have a protective effect in developing some forms of cancer but little is known about how this protective effect is manifested. There is also some evidence to suggest that physical exercise can prevent a recurrence or even prolong the life of those living with metastatic cancer, however the volume of data is limited.
More research needs to be done in a controlled setting to establish a causal effect. In the meantime, I strongly believe that people living with metastatic cancer should be encouraged to engage in physical activity to protect themselves from the known physical stress that treatment puts on their bodies. Exercise is one of the most important ways in which we can help our bodies withstand the widest array of treatment available which ultimately improves our prognosis.