Immunology is the study of the physiological mechanisms that allow the body to recognize materials as foreign and to neutralize or eliminate them. When working properly it protects us from disease and infection. Antigens are what we refer to when a foreign substance that elicits an immune response; COVID 19 is an example of a virus/antigen.
As a covering for most of the body, the skin offers the first and best line of protection. This is why hand washing is the most important thing a person can do to decrease exposure to an antigen.
But what happens when we get exposed? When an antigen enters our body through our respiratory system for example, there are innate immune responses such as phagocytic cells, cells that release inflammatory mediators and natural killer cells. Phagocytes act to eat and then kill the foreign microorganism. Neutrophils are numerous in white blood cells and can directly kill invading organisms but will also damage the host tissue. Natural killer cells recognize virally infected cells and directly attack and kill these cells. They sometimes also kill the body’s normal cells.
Now that we have a little bit better understanding of the immune system, let’s talk about how exercise plays a role in both making it stronger and weaker.
Exercise Physiologist, David Nieman, has spent the last 40 years studying the link between exercise and immunology.
Below is a J graph visually explaining the connection between risk of developing an infection and exercise. The resource for this graph can be found here.
Depending on the intensity and duration exercise can either enhance or suppress the immune system. Research shows that regular, moderate exercise will boost your immune system and your risk for developing an infection goes down, compared to a sedentary individual and an average risk. However, as you start to increase the amount and intensity of exercise, the risk for developing an infection also increases to surpass the risk of those that exercise moderately or do not exercise at all.
So, what is happening here to your immune system when you exercise for longer durations and greater intensities?
Many mechanisms appear to be involved in the acute immune response to exercise, including exercise-induced changes in stress hormone and cytokine concentrations, body temperature changes, increases in blood flow, and dehydration (Brenner et al., 1995; Cupps and Fauci, 1982; Pedersen and Ullum, 1994).
Immune function also declines with age, however, those individuals that regularly exercise as they age have immune systems of those 20-30 years younger than them.
How much is too much too much and how hard is too hard? Unfortunately, the answer isn’t as clear as we would like it to be.
Neil Walsh, an exercise immunologist at Liverpool John Moores University in Britain, compared the effects of two hours of low-intensity running with 30 minutes of high-intensity running. The longer bout disrupted immune response more than the shorter one, suggesting that duration is a bigger risk factor than intensity.
That may be because prolonged exercise depletes the fuel stores that your immune cells rely on – an effect that seems to kick in after about an hour and get even worse after 90 minutes, according to David Neiman.
David Neiman suggests a 60/60/60 rule: no more than 60 miles/week, no longer than 60 minutes at a time and keep the intensity at or below 60% of your max HR. Adding surges in are absolutely fine and your immune system seems to tolerate intermittent exercises well, so doing a run walk program does not have the same detrimental effect on your immune system as continuous running seems to.
Other suggestions are if you do need to run longer or faster, then allow yourself plenty of sleep (8-9 hours), stress management and immune boosting nutrition. It takes 6-24 hours for the immune system to recover from the acute effects of severe exercise, so another possible solution can be to spread your long run out over a 24-hour period to allow some immunity recovery between runs.
Neiman believes the key nutrient bonding exercise and good health is carbohydrates: before, during and after running. Indeed, he notes a whole new science of immuno-metabolism that puts glucose and glycogen in the center of healthy immunity just as they are key to strong endurance running.
“So, we feel that anything that can keep the blood glucose response at a near flat-line level, should attenuate the stress hormone response and then, in our hands, we have shown that then the immune system is less suppressed” David Nieman.
Now I am not saying you should run to Dunkin and grab yourself a donut. Remember to keep eating real, whole foods to always support a healthy immune system and Nieman has long been interested in polyphenols, flavonoids and other food substances that support immunity. These are mostly found in blue, purple, red and orange fruit, and to a lesser extent in colorful vegetables. In a soon-to-be published paper, he looked at the effect of eating 1 cup of blueberries daily to knock down the pro-inflammatory markers after endurance training.
Intense exercise during an infection episode should be avoided. Remember the neck check: if symptoms are above the neck in the ABSENCE of a fever, exercise should be performed cautiously and slowly. If, after 10 minutes, the symptoms are alleviated the workout can be finished with the usual amount of frequency and duration, intensity.
If you have any other questions or comments, please leave them below or email me for further discussion. Thank you for reading!