Exercise and the Immune System - Part 1

With the postponing of large sporting events including the 2020 Tokyo Olympics due to COVID-19 many athletes and support staff are looking for innovative ways to maintain and improve the sporting skills and level of physical preparedness with lack of space and facilities and social distancing. The benefits of exercise training for those individuals competing in sport is well known and documented. In the general population exercise is shown to prevent many non-communicable diseases like diabetes and cancer (1), which encourages individuals to maintain their level of fitness through home programmes even during lockdown periods.

In times where the world is faced with infectious disease pandemics, especially those of the upper respiratory tract such as COVID-19 and SARS, it brings us to question what role exercise has in moderating the immune system with respect to communicable diseases. Does exercise improve or depress immune function? What can you do to maintain immune health while exercising? How can we mitigate the risk of depressed immune function for those who are at risk such as individuals in high social contact jobs, the elderly and diseased populations?

These questions bring us to a more recent field of study (beginning in the mid-1980s) called Exercise Immunology, that explores the effect that exercise, both acute and chronic, has on various aspects of immune function. There is evidence for a single bout of strenuous and prolonged exercise depressing the response of the immune system and putting an individual more at risk of acquiring an infectious disease (2)(3). On the other hand, moderate exercise in the long term has shown in some research to improve the response of the immune system (4)(5).

Though the evidence for the relationship between exercise and immune system function may seem contradictory, it can easily be explained by the figure below.

(Adapted From Nieman, C., Johanssen, & Lee, 1989) (6)

As shown in the figure, the relationship between exercise and infection risk can be described with a ‘J’ curve’ (7). Individuals participating in regular, moderate amounts of exercise have improved immune function compared to sedentary individuals and therefore reduced risk of getting URTIs like colds, sore throats, and the flu. On the other hand, individuals participating in high-volume and intensive exercise have higher risk of URTIs due to depressed immune function.

This means that individuals who are inactive or sedentary have a less robust immune system than those who participate in moderate amount of exercise and are therefore more vulnerable to infections (8)(9). Taking part in regular exercise training also has implications for reducing the risk of lifestyle diseases such as diabetes, heart disease and metabolic syndrome, overall well-being, and lifespan. Thus, for the general population, taking part in regular exercise is beneficial from both an overall health perspective and to improve immune function.

So how is this relevant for those participating in sport? Athletes, especially those with a high amount of training load seem to be more at risk of having their immune systems compromised as a result of large amounts of training. Athletes at risk include those who are doing large volume of training such as endurance and ultra-endurance athletes, athletes undergoing a concentrated loading or an overreaching phase, as well as athletes who are over-trained.

Other important factors such as lack of sleep, under-recovering, nutritional deficiencies, under-fuelling and life/psychological stresses (such as loss of a loved one and exam season) also contribute to reducing the function of the immune system and putting a person more at risk of infection (10)(11)(12)(13). There is also evidence that the period immediately after an intense and long bout of exercise (90 minutes or more) leaves a person temporarily more susceptible to infection (14)(15).

While there are many aspects related to exercise and lifestyle that could compromise your immune health, there are also many measures and management strategies that a person could take to ensure that they mitigate the risk of a compromised immune system and continue to take part in exercise training. This will be addressed in part 2 of the article. The benefits of regular exercise far outweigh the risks for the general population (15), including in maintaining their immune function. To know more about what else you can do to maintain immune health stay tuned for part 2.

References:

1. Anderson, E., & Durstine, J. L. (2019). Physical activity, exercise, and chronic diseases: A brief review. Sports Medicine and Health Science, 1(1), 3-10.

2. Nieman, C., D., Johanssen, L. M., & Lee, J. W. (1989). Infectious episodes in runners before and after a roadrace. The Journal of sports medicine and physical fitness, 29(3), 289-296.

3. Walsh, N. P., & Oliver, S. J. (2016). Exercise, immune function and respiratory infection: An update on the influence of training and environmental stress. Immunology and cell biology, 94(2), 132-139.

4. Chubak, J., et al (2006). Moderate-intensity exercise reduces the incidence of colds among postmenopausal women. The American journal of medicine, 119(11), 937-942.

5. Akimoto, T. et al (2003). Effects of 12 months of exercise training on salivary secretory IgA levels in elderly subjects. British journal of sports medicine, 37(1), 76-79.

6. Nieman, C., D., Johanssen, L. M., & Lee, J. W. (1989). Infectious episodes in runners before and after a roadrace. The Journal of sports medicine and physical fitness, 29(3), 289-296.

7. Nieman, D. C. (1995). Upper respiratory tract infections and exercise. Thorax, 50(12), 1229-1231.

8. Campbell, J. P., & Turner, J. E. (2018). Debunking the myth of exercise-induced immune suppression: redefining the impact of exercise on immunological health across the lifespan. Frontiers in immunology, 9, 648.

9. Nieman, D. C. (2012). Clinical implications of exercise immunology. Journal of Sport and Health Science, 1(1), 12-17.

10. Cohen, S., Tyrrell, D. A., & Smith, A. P. (1993). Negative life events, perceived stress, negative affect, and susceptibility to the common cold. Journal of personality and social psychology, 64(1), 131.

11. Bishop, N. C., Blannin, A. K., Walsh, N. P., Robson, P. J., & Gleeson, M. (1999). Nutritional aspects of immunosuppression in athletes. Sports Medicine, 28(3), 151-176.

12. Edwards, J. P., Walsh, N. P., Diment, P. C., & Roberts, R. (2018). Anxiety and perceived psychological stress play an important role in the immune response after exercise. Exerc Immunol Rev, 24, 26-34.

13. Gleeson, M., & Walsh, N. P. (2012). The BASES expert statement on exercise, immunity, and infection. Journal of sports sciences, 30(3), 321-324.

14. Peake, J. M., Neubauer, O., Walsh, N. P., & Simpson, R. J. (2017). Recovery of the immune system after exercise. Journal of Applied Physiology, 122(5), 1077-1087.

15. Nieman, D. C., & Wentz, L. M. (2019). The compelling link between physical activity and the body's defense system. Journal of sport and health science, 8(3), 201-217.