Is Exercise a Pro to your Immune System, or a Con?

We all know that exercising is beneficial for our health. Getting in workouts and staying active has a host of short term and long-term positives. Beyond our muscles and ligaments, we know exercise helps with heart health, gut health, blood sugar regulation, even brain health. My physiology professor once said, “if we could put ‘exercise’ into a pill, it would be the best seller in the world.” But, have you thought about what exercise will do to your immune system? How does it affect your immunity? Does it benefit and boost your immune system, or does it weaken it? Many of these questions get asked, especially during this time of Covid-19.

Scouring through the research, I found that the literature on this topic is conflicting and more complex than a simple yes or no answer. There have been mixed messages from the medical community on the efficacy of exercise and its impact on the immune system for decades. It all started from publications from the 80s and 90s that amalgamated data into a theory called the “open-window” hypothesis, which states that the immune system is compromised in the hours after vigorous exercise, leading to an increased risk of opportunistic infections in the days thereafter.

However, the latest research shows otherwise, that living a physically active lifestyle reduces the potential for disease. This implies that immune competency is enhanced by regular exercise bouts. More specifically, studies have shown the effects of physical activity on the immune system strongly depends on the type and intensity of exercise.

How does exercise affect the immune system?

Exercise impacts our body on multiple levels and launches multiple endogenous protective and repair systems by altering gene expression and releasing a range of factors that prepare the body for the next challenge. Without getting too technical, recent studies have shown that there is an increase in various immune factors and activation during and after strenuous exercise⁠1.  Furthermore, during the recovery periods (24 hours after exercise), all these immune factors had elevated concentrations of different kinds of immune cells and activity.

However, there is a limitation of 4 hours of strenuous exercise, where subjects like marathon runners, did not benefit with this type of response from their immune system. Instead, we see a decrease across the board of immune factors after a session of more than 4 hours.  Scientists believe that the decrease in immune factors isn’t actually a lowering of the immune system, but an adjustment or reset of the immune system, coined ‘immune surveillance.’ Despite lower overall quantities of immune factors, there is a redistribution of immune factors to specific sites affected by exercise (i.e. lungs, gut). The areas that have an increased risk of encountering pathogens therefore have a heightened immune surveillance to protect the body during longer exercise sessions.

One study explored the effects of different exercise intensities, from moderate and high intensity exercise to exercising to exhaustion. They found that although saliva flow decreased, the immune factors in saliva, such as immune protein IgA, actually increased in response to both of the exercise intensities. So even though the salivary response had decreased, the concentration of IgA was higher.

Can we influence how exercise affects the immune system?

The simple answer is YES! One example of this is the inflammatory effects of our Omega-6:Omega-3 (n-6/n-3) ratio. An ideal ratio of 6:1 can abolish post-exercise immunosuppression. If this ratio is shifted in favour of omega-6, it can result in an increased production of pro inflammatory markers thus resulting in immune suppression. Similarly, other studies showed that during stressful conditions, ­omega-3 fatty acids may counteract latent immunosuppression.  These results also revealed that not just exercise plays a role in immunomodulation, but diet and nutrition also play an interactive role for boosting your immune system. Measuring your omega-6:omega-3 ratio is a simple and effective way of assessing how exercise will affect your immunity. Optimizing this to a 6:1 ratio will help ensure your exercise is working for you, not against you.

In short, exercise contributes to immune surveillance and the boosting of your immune system.  People who regularly exercise can increase their immune surveillance and immune activation.  We now know that the behaviour of almost all immune cell populations in the bloodstream is altered in some way during and after exercise⁠2.  That there is clear evidence that habitual physical activity is also anti-inflammatory and protective against developing chronic inflammatory disease.⁠3  Furthermore, evidence also shows that a physically active lifestyle diminishes the risk of contracting a range of communicable diseases including viral and bacterial infections.2 In fact, it appears to be a highly specialized and systemic response where exercise redeploys immune cells to peripheral tissues (e.g., mucosal surfaces) to conduct immune surveillance. Here, these immune cells are thought to identify and eradicate other cells infected with pathogens, or those that have become damaged or malignant, termed the acute stress/exercise immune enhancement hypothesis.2


  1. Pedersen, B. K. & L. Hoffman-Goetz. Exercise and the Immune System: Regulation, Integration, and Adaptation. 01 JUL 2000https://org/10.1152/physrev.2000.80.3.1055
  2. J.P. & J. E Turner. Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan. Front. Immunol., 16 April 2018 |
  3. M. D. et. al. Exercise and Gut Immune Function: Evidence of Alterations in Colon Immune Cell Homeostasis and Microbiome Characteristics with Exercise Training. Immunol Cell Biol. 2016 Feb;94(2):158-63. doi: 10.1038/icb.2015.108. Pub 2015 Dec 2.

Additional References:

  • Kakamas, M. W. et. al. The open window of susceptibility to infection after acute exercise in healthy young male elite athletes. Exec Immunol Rev. 2010;16:119-37.
  • Karstoft, K. & Pedersen, B. K. Exercise and Type II Diabetes: Focus on Metabolism and Inflammation. 01 December 2015.
  • Krüger, K. et. al. The Immunomodulatory Effects of Physical Activity. Curr Pharm Des. 2016;22(24):3730-48. doi: 10.2174/1381612822666160322145107.
  • Lang, Jason E. The Impact of Exercise on Asthma. Allergy and Clinical Immunology: April 2019 – Volume 19 – Issue 2 – p 118-125. doi: 10.1097/ACI.0000000000000510
  • Mathur, N & B. K. Pedersen. Exercise as a Mean to Control Low-Grade Systemic Inflammation.  doi:
  • Onanong, M. et. al. Physical Exercise Inhibits Inflammation and Microglial Activation. Cells 2019, 8(7), 691;
  • Petersen, A.M.W. & B. K. Pedersen. The Anti-inflammatory Effect of Exercise. J Appl Physiol (1985). 2005 Apr;98(4):1154-62. doi: 10.1152/japplphysiol.00164.2004.
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Ken Chu, Naturopathic Doctor

Ken J. Chu is a practicing naturopathic doctor and a board member of the Integrated Association of Naturopaths in Hong Kong. After obtaining his Bachelors Degree in Biological Sciences, Ken then graduated from the Canadian College of Naturopathic Medicine (CCNM) in Toronto. Ken practices a holistic healing approach, using a combined approach of clinical nutrition, homeopathy, and herbal medicines to address the root causes of his patients’ problems.

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