We all know someone who has been through the traumatic and sadly often fatal ordeal of a cancer diagnosis and subsequent treatment. The UK has made strides to inform the population to the common risk factors for cancer and the benefits of exercise. They roll off the top of your head as easily as your home address or your number. However, we also choose to ignore the advice that successive government health campaigns and even the education system itself has taught us over the years.
This article aims to elucidate the effects of exercise on cancer genesis and progression.
Exercise has profoundly positive effect on our immune system and the effect is almost instantaneous. The immune system is our body’s way of fighting off foreign cells such as viruses or bacteria, it plays a part in inflammation and importantly it also has a role in tumour suppression and prevention.
The evidence for the role of exercise on the immune response was first discovered in 1893. It first described how leukocytes (white cells) increased in the bloodstream during physical exertion. The link between exercise and activation of the immune system had now been observed.
The focus of recent studies in the field has been on a specific type of white blood cell (WBC) called a ‘natural Killer’ cell (NK cell) NK cells are produced in the bone marrow from CD34+ precursor cells and are part of the innate immune system and respond rapidly to threats in the body. NK cells are stored in the spleen and the vascular bed and during exercise, both of these organs have their blood flow increased significantly, and also increases their numbers in circulatory system.
NK cells have a ‘natural’ ability to seek and destroy premalignant and malignant cells without the need to first be exposed to the cell in order to develop a defence (adaptive immunity) However, they do play a major part in training the adaptive immune system.
Credit: Trends in Molecular Medicine.
Research has suggested that NK recruitment into the bloodstream can increase six fold in as little as 70 seconds of physical activity. Whereas, other studies have shown that NK increases in the bloodstream can be produced within minutes of exercise taking place. This is also in agreement with other studies that have investigated the role of exercise and white cells. However, following 30mins of endurance exercise, NK cell numbers did not increase. The general consensus in the literature is that the exercise intensity to elicit an increase in NK numbers must be sufficient for an increased heart rate and breathlessness to occur. Moderate to high intensity endurance and resistance type activities. However, exercise beyond 3 hours results in a decrease in circulating NK cells.
Research supports evidence for the benefits of exercise that we can all relate to. Overtraining can cause harm and lead to opportunistic infections that would have otherwise been dealt with by the immune system. A possible example of this is the middle distance runner Sebastian Coe and the American sprinter Carl Lewis. Two such examples of how over training may have been detrimental to success. Seb Coe failed to qualify for the 1988 Seoul Olympics due to a respiratory illness whilst Carl Lewis failed to qualify for the 1992 Olympic 100m due to an infection. While the evidence linking over training to their respective failure to qualify is not sufficient for a definitive answer. The circumstantial evidence would certainly point in that direction.
The two different subtypes of NK cells that are activated during and post exercise are known as CD56dim and CD16+ compared to all other NK cell subtypes. CD56dim and CD16+ cells are more cytotoxic (cell destroying) than other subtypes which are said to be more cytokine (molecular signalling) producing NK cells.
Cytokines are the messengers of the immune system. They are produced in certain WBC’s in order to ‘communicate’ or signal other cells of the immune system. Exercise releases myokines from the muscle fibres into the circulation. Myokines are proteins released by the muscle during contractions. The myokines are signalling molecules that activate the NK cells. Interleukin 6, 7 and 15 (IL 6, IL7 & IL15) have been seen to play a role in NK cell activation during exercise. Furthermore, epinephrine release pre and during exercise is also thought to recruit NK cells into the circulatory system.
Cytokine Map: This image shows you the different cytokines and their functions.
The role of exercise intensity, mode and duration of exercise and the various signalling pathways that activate the tumour fighting NK cells is now a bit more transparent. This could help fitness professionals to widen the scope of exercise.
The increasing body of research that has examined the effects of exercise and aging on cancer and the immune system. The general consensus is that exercise still has the same positive effect on reducing the risk of malignancies developing.
The ageing process is a complex topic involving many different variables that all contribute to the process. However, in essence, the ageing process can be thought of as an accumulation of cellular damage over time. This can be from free radical exposure and oxidative stress on cells leading to in effect cellular exhaustion. Therefore, leading to cellular dysfunction. However, the already established immediate responses of NK cells to exercise is supported by research that also suggests that elderly populations who undergo a 12 week aerobic and resistance training programme display increased antigen expression on monocytes (immune cell), decreased inflammation and inhibit a tumour promoting environment whilst promoting a tumour suppressive one.
There are studies that explore the immune response to exercise in people who have been diagnosed with cancer. The findings are in agreement with research looking into non cancer patients. The same NK cell response is seen in healthy populations and in control groups or people with malignancies. However, there is still a great deal to be done to find out if the immune response seen in both populations has any beneficial effect on clinical outcomes.
Exercise has a profound effect on blood flow around the body. Blood flow is shunted from some organs and redirected to the working muscles during exercise. The redirection of blood flow is to adequate supply the working muscles with oxygen and remove the waste products produced from cellular respiration.
Tumours exhibit hypoxia like conditions due to metabolic and blood vessel abnormalities that mean that oxygen delivery is impaired making the tumour rely on the glycolysis energy pathway for the tumour cells energy needs instead of the oxidative phosphorylation pathway. This is termed the ‘Warburg effect’
Exercise is also responsible for activating HIF1ɑ which also enables up regulation of pro-erythrocyte proteins and proteins that promote angiogenesis (increase in vasculature) Several studies have suggested an increase in intratumoral (within tumour) perfusion rate (blood flow) The increase in tumour blood flow sounds counter intuitive and far from being a benefit. However, if blood flow to the tumour is stabilised, would it mean that the tumour will have an increased nutrient supply? Therefore, promoting tumour growth? The counterargument to this is as follows; If the intratumoral vascular network is stabilised, this would increase oxygen supply bringing the tumour to normoxic (normal oxygen levels) conditions, altering tumour metabolism and up regulating AMPK and reducing tumour growth. Furthermore, increased intratumoral blood flow also increases Immune cell infiltration and allows easier access for exogenous chemotherapy drugs conferring a possible survival advantage for the patient.
Credit: Research Gate.Net
Caution must be ascribed when interpreting the effect of exercise on tumour metabolism. There are many other factors and genetic mutations affecting metabolism and tumorigenesis where exercise may or may not have an effect upon. There is still much more research to be done on human models.
Interestingly, there is an increasing body of research that examines the mode of exercise and its effects on cancer risk. Research has suggested that moderate to vigorous exercise lowered the risk of a range of cancers including; colon (23%), breast (12%), renal (12%), prostate (10%), pancreatic, gastroesophageal (18%) and ovarian (11%).
Studies using rodent models of cancer have used various types, duration, distances and intensities of exercise. The researchers postulated a dose dependent relationship between exercise and tumorigenesis. However, they did conclude that more research needs to be done to determine the exercise dose.
We can see why the UK government recommends that the adult population needs at least 30 mins of moderate to vigorous physical activity per day. The benefits of exercise are clear. Moderate to vigorous aerobic exercise and resistance training has been shown to have a positive effect on the prevention of cancer. Cancer patients could also benefit from exercise in combination with other treatments such as surgery, chemo and radiotherapy.
For those of us who are lucky enough not to have suffered cancer, a balanced, healthy diet with plenty of exercise will reduce your overall risk of developing cancer. Increased activation of the immune system. Increased exercise induced vascularisation, altered tumour metabolism and more.
Current fitness and exercise qualifications only make reference to the benefits of exercise and its cancer prevention properties. There is little to no explanation of why this is so. This can be detrimental to the overall task of educating a populace to enable them to prevent the onset of this dreadful disease.
As certain as one can be, current fitness professionals may not possess the knowledge to effectively train a cancer patient. (or a one in remission) Given that cancer will affect at least 50% of the population, the notion that fitness professionals do not have this skill set is alarming.
The way forward is for qualification awarding bodies to revamp their qualifications to include much more content on training different populations other than stereotypes of clients who ‘just wants to get bigger’ or ‘lose weight’. A reality of towns and cities across the UK is that people have all sorts of ailments and idiosyncrasies. The time for catering for a select few is now over as reality catches up with rigid qualification structures, content and teaching practices.
This is where SFE Academy is different, the courses we offer have been ‘reality checked’ meaning that we have put the course through quality checks to make sure that what we teach you is relevant to the people you are likely to encounter.
We work closely with industry partners to make sure that once qualified, you are ready for the fitness industry. .