Exercise and the Immune System
Exercise and the Immune System
Keep moving! Exercise helps maintain a healthy immune system.
Physical activity is a form of stress on the body and as such, your body releases stress hormones during exercise. During your workout, your immune system responds to these stress hormones by releasing immune factors (most notably T cells, B cells, and Natural Killer or NK cells) to help the body in this perceived ‘fight’.
Once you finish exercising and the physical stress is over, the immune system needs recovery time to replenish any immune cells to pre-exercise levels so that it is ready to defend against bacterial or viral invaders that may come your way - the real ‘fight’. The intensity of the exercise that you do really defines whether it is beneficial or not to your immune system in the presence of other immune threats.
Can exercise build immunity?
The short answer is yes! But the intensity level of your exercise matters. Specifically, high intensity exercise can temporarily suppress the immune system, which could lead to increased risk of infection. This effect lasts for about 3 to 72 hours after exercising, and some studies have linked this to a higher occurrence of upper respiratory infection symptoms post strenuous exercise. This means that our bodies may have an “open window of altered immunity” which makes it even more important to allow for adequate rest and recovery.
‘High Intensity’ exercise is defined as prolonged, continuous exercise (duration greater than 1.5hrs) at 55-75% aerobic capacity, performed prior to food intake.
What should you do instead? Moderate intensity is the way to support immunity.
In contrast to the suppressant effects of high intensity exercise, studies have shown that regular, moderate exercise reduces your overall risk of infection, especially compared to a sedentary lifestyle. In one study, individuals who participated in moderate intensity aerobic exercise at least 5 times per week rated themselves as more physically fit than those who exercised one day per week or less. Those who exercised at least 5 times a week were also less likely to suffer from upper respiratory infections. This is because moderate intensity exercise boosts key components of the immune system (including NK cells) and enhances the body’s systemic anti-inflammatory effects. There is also no “open window of altered immunity” effect associated with risk of infection, as there is with high intensity exercise.
How can you optimize your routine to best support your immune system?
Considering the importance of supporting immune function, now is the time to optimize your workout routine.
Alternate long, intense workouts with rest (sleep). In between workouts, active recovery helps to ease the load on your immune system, and can decrease stress as well!
Participate in regular low-to-moderate intensity workouts, such as cycling, jogging, body weight exercises, hiking, etc.
If you can, try to move your body every day!
Finding a new routine can be tricky, but I encourage you to keep your immune system functioning optimally by keeping up with healthy habits, hydrating, eating well, getting lots of sleep, and including moderate intensity exercise into your daily activities.
References:
Gleeson, M., N.C. Bishop, and N.P. Walsh (eds.) (2013). Exercise Immunology. Abingdon: Routledge.
Gleeson, M., N.C. Bishop, D.J. Stensel, M.R. Lindley, S.S. Mastana, and M.A. Nimmo (2011). The anti-inflammatory effects of exercise: mechanisms and implications for the prevention and treatment of disease. Nat. Rev. Immunol. 11:607-615.
Nieman, DC. Immune Response to heavy exertion. Journal of Applied Physiology, 1997;82: 1385-1394.
