Impacts of Exercise on Immune Function

Common known benefits of exercise are increased fitness, metabolic improvements, changes to composition, benefits to mood, and increased socialization. A less known impact of exercise is that it has significant effects on immune function. 

Both cross-sectional and longitudinal studies in humans have illustrated the profound impact of exercise on the immune system with evidence of enhanced immune surveillance (defense/protection) and repair functions.   

Benefits of Exercise on Immune Function:

1. Stimulates cellular immunity.   Moderate-intensity exercise can boost cellular immunity by increasing the circulation of immune cells in the body.  This enhanced immune cell movement helps identify and combat pathogens more effectively.  
2. Reduces upper respiratory tract infections (URTI).  Epidemiological studies consistently show that physically active individuals experience fewer URTIs compared to sedentary people.  
3. Lowers chronic low-grade inflammation. Regular exercise reduces fat mass and associated tissue inflammation.  Exercise also increases muscle production of IL-6 and T regulatory cells which increase anti-inflammatory immune signaling.
4. Improves various immune markers in several disease states.  Data shows exercise has a positive impact on chronic diseases such as cancer, HIV, cardiovascular disease, diabetes, rheumatoid arthritis, dementia, and obesity. 
5. Intensity and frequency matters.  Moderate intensity exercise training appears to be protective against illness and associated symptoms.  Regular activity over time produces greater immune benefits.  
6. Long-lasting effects.  Physical activity not only gets immune cells moving during exercise, but also promotes their presence for up to three hours after exercise.
7. Improved immune responses to vaccination.  Regular exercise leads to a stronger antibody response, enhancing protection against infections.

Does prolonged high-intensity/high-volume exercise compromise immune function?   

Within the field of exercise immunology, there is data showing that repeated high-intensity/high-volume bouts of exercise have transient impacts on the immune system.  These include the following:

1. Suppressed mucosal and cellular immunity
2. Increased symptoms of upper respiratory tract infections 
3. Increased allergic hypersensitivity 
4. Latent viral reactivation (such as Epstein-Barr Virus or herpes simplex virus)
5. Impaired immune responses to vaccine and novel antigens (I.e.: new bugs) 
6. Potential impacts to microbiome diversity and intestinal membrane permeability 

There is an ongoing debate in the exercise immunology literature trying to better understand the effects of high-intensity/high-volume exercise on immune function.  The current data suggests that infection susceptibility in response to high-intensity/high-volume exercise is multifactorial in nature. 

Factors such as genetics, sleep, psychological stress, circadian misalignment, nutritional status, diversity of the gut microbiome, intestinal permeability and underlying conditions that promote inflammatory processes are thought to contribute to the varied immune response and infection risk observed in studies evaluating the impacts of strenuous exercise.  

An Opportunity for Personalized Medicine 

The field of exercise immunology continues to explore the effects of exercise on immune function and is now powered by advances in technology to evaluate complex variables simultaneously. 

While the science is still underway, this is a fantastic opportunity for personalized medicine to help individuals better understand how factors such as stress, nutrition, sleep quality, and circadian rhythm interact with exercise demand to help maximize the effects of exercise on immune function.  We can put these principles into practice. Consider this:   

1. Do a “N-of-1” trial.  Personalized medicine gives space for performing little experiments on yourself and using the power of observation to watch how your body responds to various environmental stimuli.  Time the experiment when you can keep other variables such as nutrition, sleep, and stress more stable.  Modify your exercise intensity, duration, frequency and see how your body responds.  See for yourself how your body reacts to variations of exercise.  For example, if you are starting with a greater systemic inflammatory burden and nutrient deficiencies, your immune system may not be as resilient.  Your exercise-immune optimization window may be lower.  Don’t worry, having this knowledge is valuable.  It gives you something to work towards.  As you improve other variables that impact immune function (nutritional state, microbiome diversity, sleep efficiency, circadian rhythm, etc.), your window of positive exercise impact can expand over time which is beneficial for your fitness and immune function!  
2. Wearables can help you see trends.  An Oura ring or other wearable is an additional tool to get more data points on yourself.  You can track measures of sleep duration and quality, resting heart rate, body temperature, or heart rate variability.  This steady stream of data can give you an idea of your baseline and then see deviations more clearly in relationship to behaviors such as exercise and recovery.  
3. Stay within the window of benefit.  Learn to look for connections between the balance of recovery and stress behaviors to find your “sweet spot.”  Note this zone is not fixed.  As discussed, there are a multitude of factors currently being debated/studied for how they interact with the immune system to either promote or detract from the immune benefits of exercise (i.e.: stress, nutrition, sleep, genetics, toxicant status, chronic infectious burden, microbiome diversity, intestinal membrane integrity).   As your overall level of health improves, your immune response to exercise increases in competency and resiliency.  
4. If you engage in regular high intensity/high volume exercise, use other dietary and lifestyle interventions more intentionally.  Synergize the best of what we know now.  Choose foods that enhance the immune response.  Prioritize sleep and recovery practices as it is well known that sleep has an immense immune benefit.  Modulate stress and create down-states to contrast your time in exercise.   Consider food specific or nutraceutical focused interventions that strengthen immune responses against viral reactivation or viral infection. 

News to Use: Exercise and Immune Connections

1. Regular bouts of short-lasting (i.e. 45 minutes) moderate intensity exercise is ‘immunoenhancing.’ 
2. Repeated bouts of long-lasting (>2hours) high intensity exercise can be ‘immunosuppressive’
3. Other factors such as genetics, nutritional status, sleep, circadian rhythm, stress, microbiome diversity are variables that potentially contribute to the body’s unique immune response to exercise at different frequencies, intensities, and durations.  
4. Personalization is key when multiple systems are involved.  Focus on optimizing the synergy of the whole body with curiosity and an open mindset to find the exercise window that best enhances immune function.
5. More of the same isn’t always better.  Improving cumulative immune function through nutrition and recovery practices can help shift your exercise sweet spot over time.  
6. Listen to your body!  If you notice you are getting sick more often or taking longer to recover, re-evaluate your relationship with exercise, nutrition, and sleep to find that window of optimization. 

References

Bonomini-Gnutzmann R, Plaza-Díaz J, Jorquera-Aguilera C, Rodríguez-Rodríguez A, Rodríguez-Rodríguez F. Effect of Intensity and Duration of Exercise on Gut Microbiota in Humans: A Systematic Review. Int J Environ Res Public Health. 2022 Aug 3;19(15):9518. doi: 10.3390/ijerph19159518. PMID: 35954878; PMCID: PMC9368618.

Colbey C, Cox AJ, Pyne DB, Zhang P, Cripps AW, West NP. Upper Respiratory Symptoms, Gut Health and Mucosal Immunity in Athletes. Sports Med. 2018 Mar;48(Suppl 1):65-77. doi: 10.1007/s40279-017-0846-4. PMID: 29363055; PMCID: PMC5790851.

Simpson RJ, Campbell JP, Gleeson M, Krüger K, Nieman DC, Pyne DB, Turner JE, Walsh NP. Can exercise affect immune function to increase susceptibility to infection? Exerc Immunol Rev. 2020;26:8-22. PMID: 32139352.

Walsh NP, Oliver SJ. Exercise, immune function and respiratory infection: An update on the influence of training and environmental stress. Immunol Cell Biol. 2016 Feb;94(2):132-9. doi: 10.1038/icb.2015.99. Epub 2015 Nov 13. PMID: 26563736.

Walsh NP. Recommendations to maintain immune health in athletes. Eur J Sport Sci. 2018 Jul;18(6):820-831. doi: 10.1080/17461391.2018.1449895. Epub 2018 Apr 11. PMID: 29637836.