Can exercise "boost" your immune system and help protect your body against infections?
What about supplements that claim to boost your immune system? Do they work? EndurElite Chief Endurance Officer Matt Mosman, MS, CISSN, CSCS has your answer in this 60-second brain bomb!
Exercise And Resistance To Infection
The concept that exercise can have both a positive and a negative effect on the risk of infection is almost two decades old. This idea was introduced by Dr. David Nieman when he described the risk of a URTI as a J-shaped curve that changed as a function of the intensity and amount of exercise being performed.
People engaging in regular bouts of moderate exercise are at a lower risk of a URTI compared to sedentary individuals and people who engage in intense and/or long-duration exercise sessions.
For example, marathon runners represent those at the high end of the exercise intensity and duration scale. Indeed, running a marathon increases the risk of a URTI in the days following the run (24).
In the next two segments, we discuss the reasons why moderate- and high-intensity exercise have different effects on the risk of infection.
Moderate Aerobic Exercise Protects Against Infection
Although controversy exists, several studies support the concept that people who engage in regular bouts of moderate aerobic exercise catch fewer colds (i.e., URTIs) than both sedentary individuals and people who engage in high-intensity/long-duration exercise (22, 23).
For example, both epidemiological and randomized studies consistently report that regular exercise results in an 18% to 67% reduction in the risk of URTI (9).
Interestingly, this exercise-induced protection against infection can be achieved with many types of aerobic activity (e.g., walking, jogging, cycling, swimming, sports play, and aerobic dance).
In general, it appears that 20 to 40 minutes of moderate-intensity exercise (i.e., 40% to 60% of V˙O2 max) per day is adequate to promote a beneficial effect on the immune system.
Importantly, this exercise-induced reduction in the risk of URTI occurs in both young adult and middle age men and women (22). Further, regular aerobic exercise appears to benefit the immune system in older individuals as well (28).
The explanation as to why moderate-intensity exercise protects against URTI remains a topic of debate. Nonetheless, there are several possible reasons to explain this.
- First, each bout of moderate aerobic exercise causes an increase in blood levels of natural killer cells, neutrophils, and antibodies (9).
- Therefore, an acute bout of exercise provides a positive boost to both the innate immune system (natural killer cells and neutrophils) and the acquired immune system (antibodies).
- Note that this exercise-induced boost in immune function is transient and that the immune system returns to pre-exercise levels within three hours.
- Nonetheless, it seems that each bout of exercise improves immune function against pathogens over a short period, which results in a reduced risk of infection (22).
- Other factors might also contribute to the positive impact of routine exercise on the reduced risk of infection. For example, people who engage in regular exercise may also benefit from an improved psychological well-being (i.e., less emotional stress), good nutritional status, and a healthy lifestyle (e.g., adequate sleep).
- Each of these factors has been linked to a reduced risk of infection and, therefore, may also contribute to the connection between regular exercise and lowered risk for URTI.
Although it appears that aerobic exercise provides protection against colds, it remains unknown if resistance exercise training provides the same level of protection against infection.
This is because few studies have systematically investigated the impact of resistance exercise on immune function.
Nonetheless, based on the available evidence, it appears that an acute bout of resistance exercise results in a transient increase in natural killer cells (15).
However, this immune boost is temporary because blood levels of primary immune cells return to normal within a short period following a resistance training session (5).
To summarize, it appears that regular bouts of resistance exercise might protect against infection, but additional research is required to firmly establish that resistance exercise alone is effective in providing protection against URTIs.
High-Intensity/Long-Duration Aerobic Exercise Increases the Risk of Infection
The idea that athletes engaged in intense training are more susceptible to infections originated from anecdotal reports from coaches and athletes.
For instance, the marathon runner Alberto Salazar reported that he caught 12 colds in 12 months while training for the 1984 Olympic marathon (17). Because Salazar was engaged in intense exercise training, many people reasoned that the high level of exercise training was responsible for his increased number of colds.
However, anecdotal reports do not prove cause and effect, and scientific studies were required to determine if intense exercise training leads to an increased risk of infection.
Although controversy exists (31), several studies support the concept that athletes engaged in intense endurance training suffer a higher incidence of URTI compared to sedentary individuals or people engaged in moderate exercise (Fig. 6.3) (9, 21, 24).
For example, compared to the general population, evidence indicates that sore throats and flu-like symptoms are more common in athletes involved in intense training (11, 24).
Indeed, the risk of developing a URTI is two- to sixfold higher in athletes following a marathon compared to the general public (24). This increased risk of illness is a concern for athletes because even minor infections can impair exercise performance and the ability to sustain intense exercise training (27).
Further, prolonged viral infections are often associated with the development of persistent fatigue, which poses another threat to the athlete (7).
There are several reasons why high-intensity and long-duration exercise promotes an increased risk of infection (9). First, prolonged (>90 minutes) and intense exercise has a temporary depressive effect on the immune system. For example, after a marathon, the following major changes occur in immune function:
- Decreased blood levels of B-cells, T-cells, and natural killer cells
- Decrease in natural killer cell activity and T-cell function
- Decrease in nasal neutrophil phagocytosis
- Decrease in nasal and salivary IgA levels
- Increase in pro- and anti-inflammatory cytokines
Collectively, these changes result in a depression of the immune system’s ability to defend against invading pathogens.
It has been argued that this immune suppression following a marathon provides an “open window,” during which viruses and bacteria can gain a foothold and increase the risk of infection (see Fig. 6.4).
The biological reason to explain why intense exercise promotes immune depression is probably related to the immunosuppressive effects of stress hormones such as cortisol (8).
High cortisol levels have been reported to depress immune system function in several ways (8).
For example, high levels of cortisol can inhibit the function of specific cytokines, suppress natural killer cell function, and depress both the production and function of T-cells (20).
Although strenuous exercise can depress immune function, other factors may also contribute to the increased risk of infection in athletes engaged in intense training.
- For example, athletes engaged in intense training may also be exposed to other potential stressors, including a lack of sleep, mental stress, increased exposure to pathogens due to large crowds, air travel, and inadequate diet to support immune health.
- Each of these factors has been reported to have a negative impact on immune function and, therefore, could contribute to the increased incidence of URTIs in athletes (9).
- Figure 6.5 summarizes the factors that may explain why athletes engaged in intense training are at a greater risk of infection.
Finally, do weeks of intense exercise training result in a chronic state of immune depression? The answer to this question is no because following an acute bout of exercise, circulating leukocyte number and function return to pre-exercise levels within 3 to 24 hours (8).
Further, comparisons of leukocyte numbers and other markers of immune function between athletes and nonathletes do not differ markedly (8). Therefore, in the resting state, immune function is not different between athletes and nonathletes.
- Exercise can have both a positive and negative effect on the risk of infection. The relationship between the intensity/amount of exercise and the risk of developing a URTI is described as a J-shaped curve (Fig. 6.3). This J-shaped curve illustrates that moderate-intensity aerobic exercise decreases the risk of infection, whereas high-intensity/prolonged exercise increases the risk of infection.
- Regular aerobic exercise can reduce the risk of infection in several ways. In particular, an acute bout of moderate exercise increases blood levels of antibodies, natural killer cells, and neutrophils that provide a positive boost to the immune system.
- The fact that moderate aerobic exercise provides a transient boost to the immune system is another example of how regular exercise can enhance a control system in the body to preserve homeostasis. Indeed, by protecting the body against infection, the immune system plays an important role in maintaining homeostasis.
- High-intensity/long-duration exercise has been shown to have a temporary depressive effect on the immune system. This acute immune suppression following an intense exercise session provides an “open window” during which viruses and bacteria can grow, resulting in an infection.
- Ahmad A, Banerjee S, Wang Z, Kong D, Majumdar AP, and Sarkar FH. Aging and inflammation: etiological culprits of cancer. Current Aging Science 2: 174–186, 2009. [PubMed: 19997527]
- Balistreri CR, Caruso C, and Candore G. The role of adipose tissue and adipokines in obesity-related inflammatory diseases. Mediators of Inflammation. doi:10.1155/2010/802078.
- Chouker A, Demetz F, Martignoni A, Smith L, Setzer F, Bauer A, et al Strenuous physical exercise inhibits granulocyte activation induced by high altitude. Journal of Applied Physiology 98: 640–647, 2005. [PubMed: 15333608]
- Coico R and Sunshine G. Immunology: A Short Course. Hoboken, NJ: Wiley-Blackwell, 2015.
- Flynn MG, Fahlman M, Braun WA, Lambert CP, Bouillon LE, Brolinson PG, et al Effects of resistance training on selected indexes of immune function in elderly women. Journal of Applied Physiology 86: 1905–1913, 1999. [PubMed: 10368355]
- Fox S. Human Physiology. Boston, MA: McGraw-Hill, 2015.
- Friman G and Ilback NG. Acute infection: metabolic responses, effects on performance, interaction with exercise, and myocarditis. International Journal of Sports Medicine 19 (Suppl 3): S172–182, 1998. [PubMed: 9722283]
- Gleeson M. Immune Function in Sport and Exercise. Philadelphia, PA: Elsevier, 2006.
- Gleeson M. Immune function in sport and exercise. Journal of Applied Physiology 103: 693–699, 2007. [PubMed: 17303714]
- Graham N. The epidemiology of acute respiratory tract infections in children and adults: a global perspective. Epidemiological Reviews 12: 149–178, 1990.
- Heath GW, Ford ES, Craven TE, Macera CA, Jackson KL, and Pate RR. Exercise and the incidence of upper respiratory tract infections. Medicine & Science in Sports & Exercise 23: 152–157, 1991.
- Heath GW, Macera CA, and Nieman DC. Exercise and upper respiratory tract infections. Is there a relationship? Sports Medicine 14: 353–365, 1992. [PubMed: 1470789]
- Jansky L, Pospisilova D, Honzova S, Ulicny B, Sramek P, Zeman V, et al Immune system of cold-exposed and cold-adapted humans. European Journal of Applied Physiology and Occupational Physiology 72: 445–450, 1996. [PubMed: 8925815]
- Klokker M, Kjaer M, Secher NH, Hanel B, Worm L, Kappel M, et al Natural killer cell response to exercise in humans: effect of hypoxia and epidural anesthesia. Journal of Applied Physiology 78: 709–716, 1995. [PubMed: 7759444]
- Miles MP, Kraemer WJ, Grove DS, Leach SK, Dohi K, Bush JA, et al Effects of resistance training on resting immune parameters in women. European Journal of Applied Physiology 87: 506–508, 2002. [PubMed: 12355189]
- Monto A. Epidemiology of viral infections. American Journal of Medicine 112: 4S–12S, 2002. [PubMed: 11955454]
- Nieman DC. Can too much exercise increase the risk of sickness? Sports Science Exchange 11 (Suppl): 69, 1998.
- Nieman DC. Current perspective on exercise immunology. Current Sports Medicine Reports 2: 239–242, 2003. [PubMed: 12959703]
- Nieman DC. Exercise, upper respiratory tract infection, and the immune system. Medicine & Science in Sports & Exercise 26: 128–139, 1994.
- Nieman DC. Immune response to heavy exertion. Journal of Applied Physiology 82: 1385–1394, 1997. [PubMed: 9134882]
- Nieman DC. Marathon training and immune function. Sports Medicine 37: 412–415, 2007. [PubMed: 17465622]
- Nieman DC, Henson DA, Austin MD, and Sha W. Upper respiratory tract infection is reduced in physically fit and active adults. British Journal of Sports Medicine 45: 987–992, 2011. [PubMed: 21041243]
- Nieman DC, Henson DA, Gusewitch G, Warren BJ, Dotson RC, Butterworth DE, et al Physical activity and immune function in elderly women. Medicine & Science in Sports & Exercise 25: 823–831, 1993.
- Nieman DC, Johanssen LM, Lee JW, and Arabatzis K. Infectious episodes in runners before and after the Los Angeles Marathon. Journal of Sports Medicine and Physical Fitness 30: 316–328, 1990. [PubMed: 2266764]
- NIH. The common cold. www.niaidnihgov/topics/commoncold, 2010.
- Peake J, Peiffer JJ, Abbiss CR, Nosaka K, Okutsu M, Laursen PB, et al Body temperature and its effect on leukocyte mobilization, cytokines and markers of neutrophil activation during and after exercise. European Journal of Applied Physiology 102: 391–401, 2008. [PubMed: 17962974]
- Roberts JA. Viral illnesses and sports performance. Sports Medicine 3: 298–303, 1986. [PubMed: 3526508]
- Simpson RJ, Lowder T, Spielmann G, Bigley A, and LaVoy E. Exercise and the aging immune system. Ageing Research Reviews 11: 404–420, 2012. [PubMed: 22465452]
- Somppayrac, L. How the Immune System Works. Hoboken, NJ: Wiley-Blackwell, 2012.
- Tiollier E, Schmitt L, Burnat P, Fouillot JP, Robach P, Filaire E, et al Living high-training low altitude training: effects on mucosal immunity. European Journal of Applied Physiology 94: 298–304, 2005. [PubMed: 15765238]
- Walsh N and Oliver S. Exercise, immune function, and respiratory infection: an update on the influence of training and environmental stress. Immunology and Cell Biology. doi:10.1038: 1–8, 2015.
- Walsh N, et al Position statement. Part one. Immune system and exercise. Exercise Immunology Reviews 17: 6–63, 2011.
- Widmaier E, Raff H, and Strang K. Vander’s Human Physiology. Boston, MA: McGraw-Hill, 2015.