Our immune system is the 'intelligent deployment of defence agents in the body’. Therefore it makes sense for us to keep this protective system not only up to date but also physically and mentally resilient.
To explain this, it helps to understand hormesis. Hormesis is defined as a favourable response to an exposure that causes stress on our bodies. When our cells experience hormesis (e.g. from exercise) our natural response is to regenerate cells, helping us keep our systems fit and younger.
Moderate and regular physical activity has been shown to do just this. It promotes an influx of immune molecules (NK cells and T cells) into our bloodstream and when aided by the adrenalin we produce during activity the cells are redeployed from our blood stream to areas of the body in need. That is, for example, mucosal surfaces of the lungs and bone marrow. It is in the bone marrow where new immune cells (e.g. lymphocytes) are made along with other new blood cells. So overtime regular, moderate exercise promotes the deployment of immune cells, strengthening our immune system.
This makes perfect sense when we find studies showing physical activity shortly before a human vaccine is administered significantly increases the body's response to the vaccine, therefore improving the outcome.
Our muscle is an important regulator of immune function...
The movement of muscles causes the release of proteins called myokines. The sole release of the myokine interleukin-6 (IL-6) in the muscle is pivotal for muscle regeneration and further stimulates the anti-inflammatory myokine IL-10, modulating our immune system. Overall, with knowledge of the interaction between muscle and immune cells, we can see the importance of retaining our muscle strength in order to sustain immune resilience.
But what about the ‘Immunity Exercise Paradox’....?
It is said that some exercise is good, more is sometimes not good and too much is bad! In the past, exercise has been termed an immunosuppressant, however more recent studies conclude that this depends on the individual and their environment.
We all have our own allostatic load (aka ‘wear and tear’) so it may depend on levels of stress, sleep, rest and relaxation. Furthermore, we may like to consider the health of our most important defence element, our gastrointestinal border. This is the largest and first area that communicates with our external environment and contains 80% of our immune system! We also must not forget about our gastrointestinal microbes (e.g. bacteria, fungi) which if balanced, provide greater support to our immune system.
Final Remarks
Research concludes that, for the most benefit, exercise should be regular, long-term and moderate.
It is recommended that like with most things in life, diversity in types of movement (walking, dancing, competing, playing) is key and should be made fun to make it habitual.
Importantly, before rushing off to embark on the Marathon des Sables you may wish to take note of your state of ‘wear and tear’. Transitional exercise, by starting small and slowly getting larger, ensuring adequate recovery, is suggested to be best along with ensuring that you are getting the right levels of nourishment from your diet and lifestyle. If in doubt, seeking advice from a health and/or fitness professional is recommended.
“If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.”
Hippocrates c. 460—377 B.C.
References:
1. Cambell and Turner 2018, Front Immunol 2018, 9: 648
2. IMMUNITY: The Science of Staying Well, by Jenna Macciochi (Book)
3. Nelke et al 2019, EBioMedicine. 2019 Nov; 49: 381–388
4. Pascoe A et al, 2014, Brain Behaviour & Immunity 2014 39:33-41
5. Simpson et al 2020, Exerc Immunol Rev. 2020;26:8-22
6. Walsh N Oliver S 2016, Immunology & Cell Biology, 2016, vol: 94 (2) pp: 132-139
7. Walsh 2019, Sports Medicine 2019 vol 49, p153–168