Key Points
- Exercise improves health and immunity
- Overtraining can reduce immunity though and make us more prone to infections
- It is also important to take in enough total energy (‘fuel’) to preserve and improve immune function along with exercise
It is widely accepted that exercise improves health and is, by extension, a valuable contributor to proper immune functioning and resistance to infection. However, excessive exercise is a stressor that can dampen immune functions and as a result, over-training can lead to increased rates of infection with colds and flu-like viruses, a situation commonly seen in athletes.
Over-exercise or over-stress from any cause is pro-inflammatory and over half of all sports injuries are also secondary to overuse.1 Markers of antioxidant status such as glutathione concentration and inflammatory markers such as interleukin 10 are affected by long periods of intense training.2 So, exercise helps to mitigate stress and fatigue and helps us to modulate inflammatory/immune and antioxidant pathways, BUT too much (over-reaching) can be just as detrimental as too little.
Overreaching and over-training syndrome in athletes is depicted as a continuum, this is also likely to be the case for generalised ‘stress’. So, excessive exercise (or any other stressor) can be thought of as stress, leading to fatigue, leading to a greater incidence of infection (and burnout).
Excessive exercise (or any other stressor) can be thought of as stress, leading to fatigue, leading to a greater incidence of infection
Moderate amounts of exercise improve immune system functions and reduce the risk of infection. On the other hand, athletes engaged in regular prolonged and intensive training can experience acute (and possibly chronic) exercise-induced changes in immune function resulting in higher than normal incidence of minor infections, especially of the upper respiratory tract (e.g. the common cold and influenza).3
Progressive exercise, within the bounds of someone’s ability to recover increases white blood cell counts.4 However, acute strenuous exercise can decrease innate immune response in both competitive athletes and healthy ‘non-athletes’.5
Also, moderate-intensity exercise is suggested to improve the function of the intestinal mucosal barrier (a key barrier to infection), while higher intensity exercise could cause intestinal barrier disruption.6 Low-intensity exercise forms like Tai Chi might also improve antioxidant activity and improve immune responses.7
Does carbohydrate supplementation protect against exercise-induced reductions in immunity?
It has long been suggested that carbohydrate supplementation improves immune responses to exercise. However, in a 2016 randomised controlled trial, while carbohydrate supplementation during a 2-hour exercise test (at 60% VO2max) reduced cortisol (one of the key ‘stress’ hormones and an inhibitor of immune function), it did not affect immune responses to a test antigen (an ‘antigen’ is a structure on the cell wall of an infectious agent that the immune system recognises and responds to.)8 In another study, carbohydrate supplementation significantly reduced the immune/inflammatory marker TNF-a post-exercise at simulated altitude conditions, an effect not seen for placebo or glutamine (with no significant effect seen in other markers of inflammation/immunity – IgA, IL-10, IL-6).9
It is most likely that energy sufficiency is more important than macronutrient intake for immunity. However, eating sufficient protein is likely to be important.
Can caffeine increase immune function with exercise?
In a 2016 randomised controlled trial, ingestion of 6 mg/kg of caffeine one hour before 20 min of high-intensity interval exercise, resulted in increased natural killer cell counts before and after exercise (after N.S.) without any significant effect on adaptive immune cells (CD4⁺ and CD8⁺ T cells).10 Bear in mind this is a large dose… 6 mg per kilo of bodyweight for me would be the equivalent of around 5 cups of coffee!
Take home message
Exercise is part of the foundation of health and has enormous benefits to overall resilience and particularly our resistance to infection. However, like anything else, the dose defines the poison! Excessive amounts of exercise are likely to reduce immunity and encourage a greater likelihood of infections, especially respiratory infections and possibly gut-related infectious disturbances too.
It is therefore important to:
- Begin any exercise routine at a level that is comfortable for you
- Increase volume and intensity slowly
- Back off the intensity and/or volume if you are feeling run-down, are getting repeated cold or flu-like viruses and if your sleep is suffering
- Consider starting with: Move for at least 20 min
per day
- Do some resistance training – start with low-volume strength training. I.e. 2-3 exercises for 1-2 sets of 3-6 reps, 2-6 x per week at a load that you can handle easily (but increase this by small increments as often as possible!)
It’s important to remember that we can habituate ourselves to increased levels of exercise and if we start at a level at which we are comfortable and not over-reacting with excessive stress responses and then incrementally increase volume and/or intensity of our training, we can increase our work threshold.
It is best to start with an almost ridiculously easy volume and intensity and then incrementally increase that to build your overall work-tolerance rather than ‘smashing’ yourself at each session. Important considerations for fatigue are that ‘grind’ lifts with a slower velocity may be preferable to explosive or ‘metabolic-style’ workouts during times of recovery from fatigue or sickness, due to the reduced volume required for neuromuscular adaptations, reduced eccentric loadings and better overall neuromuscular adaptations post-exercise.11 Longer rest periods (more than 2 min rest between sets) also preferred for those in the recovery phase from fatigue and these facilitate an improved free-testosterone to cortisol ratio.12
References
1. Wilder RP, Sethi S. Overuse injuries: tendinopathies, stress fractures, compartment syndrome, and shin splints. Clinics in Sports Medicine. 2004;23(1):55-81.
2. Varamenti EI, Kyparos A, Veskoukis AS, Bakou M, Kalaboka S, Jamurtas AZ, et al. Oxidative stress, inflammation and angiogenesis markers in elite female water polo athletes throughout a season. Food and Chemical Toxicology. 2013;61:3-8.
3. Jones AW, Davison G. Chapter 15 – Exercise, Immunity, and Illness. In: Zoladz JA, editor. Muscle and Exercise Physiology: Academic Press; 2019. p. 317-44.
4. Ghobadi MR, Dehaghani ST, Nazari M. The effect of altitude and progressive exercise activity on the profile of testosterone changes and Some of immunity markers in active student basketball team. Physical education of students. 2020;24(1):47-54.
5. Kurowski MM, Jurczyk J, Pawelczyk M, Szulc A, Krysztofiak H, Kowalski ML. Treadmill exercise decreases expression of innate immunity molecules in peripheral blood leukocytes in competitive athletes, asthmatics and healthy subjects. European Respiratory Journal. 2016;48(suppl 60):PA571.
6. WU D, CHEN P-j, LUO B-b. Effect of Exercise on Intestinal Barrier Function and Mucosal Immunity Homeostasis. China Sport Science. 2018(6):8.
7. Niu A. Effect of “Tai Chi” exercise on antioxidant enzymes activities and immunity function in middle-aged participants. African Journal of Traditional, Complementary and Alternative Medicines. 2016;13(5):87-90.
8. Davison G, Kehaya C, Diment BC, Walsh NP. Carbohydrate supplementation does not blunt the prolonged exercise-induced reduction of in vivo immunity. Eur J Nutr. 2016;55(4):1583-93.
9. Caris AV, Da Silva ET, Dos Santos SA, Tufik S, Dos Santos RVT. Effects of Carbohydrate and Glutamine Supplementation on Oral Mucosa Immunity after Strenuous Exercise at High Altitude: A Double-Blind Randomized Trial. Nutrients. 2017;9(7):692.
10. Thida K. Does Caffeine Consumption before High-Intensity Intermittent Exercise Enhance Immunity? : Auckland University of Technology; 2016.
11. Lopes CR, Crisp AH, Rodrigues AL, Teixeira AG, da Mota GR, Verlengia R. Fast contraction velocity in resistance exercise induces greater total volume load lifted and muscle strength loss in resistance-trained men. Revista Andaluza de Medicina del Deporte. 2012;5(4):123-6.
12. Rahimi R, Rohani H, Ebrahimi M. Effects of very short rest periods on testosterone to cortisol ratio during heavy resistance exercise in men. Apunts Medicina de l’Esport. 2011;46(171):145-9.
