Exercise and Immune Function

What Dosage is Most Beneficial?

It’s easy to get into an exercise slump these days while dealing with the current COVID pandemic. Our beloved gyms are closed, there are no group exercise classes, no organized running races, no PE to stress about getting ready for, etc. Not surprisingly, some people (or many people) have gotten off their normal schedule and have dropped off the exercise train altogether. While this is completely understandable, considering we are all just trying to survive and stay healthy, it is not healthy for our overall health and more importantly, the immune system. Exercise is literally the “magic pill” for many common health conditions: lowers blood pressure and cholesterol, protects against heart disease and stroke, improves mental health, and the list goes on and on. The span of exercise benefits broaden everyday as the breadth of research expands, so much so that gym memberships should be subsidized by health care companies, but this is a whole different topic. Recent studies have also shown that exercise is beneficial to the immune system. Add that to the list of benefits of this seemingly all healing treatment! There is some recent research that shows that even a single bout of exercise can improve immune function, most likely by opening up blood vessels and allowing blood cells to do their job efficiently [1].

Great! Now get out there and go run a marathon! This relationship proves to be more complex than just, “do more exercise.”  Not so fast… the type of exercise is also important to this whole beneficial equation. According to the popular J-curve theory, displayed below, moderate exercise provides a decrease in upper respiratory tract infections (40-50% decrease), then as exercise intensity ramps up, the protective effect diminishes and actually has been shown to dramatically increase one’s risk of upper respiratory infections and therefore decrease immune function [2]. Unfortunately like anything else in life, too much exercise can be dangerous to your health as well. Especially in a world where the strength of our immune system is pivotal to our overall health.

But how does one define “high workload” or “heavy exertion” exercise? This is a tough question because it is dependent on each individual (fitness level, stress level, underlying health issues, type of usual exercise, etc.). Also, is exercise workload defined as duration, intensity or frequency? Neil Walsh, an exercise immunologist at Liverpool John Moores University in Britain performed a study in which he compared the effects of 2 hours of low-intensity running with 30 minutes of high-intensity running. He found that the longer bout of exercise disrupted immune function more than the shorter bout, suggesting that duration was a bigger detriment than intensity. Walsh also did a separate study that studied external factors such as stress and disrupted sleep on immune function which showed that anxiety and psychological stress had just as much effect on suppressing immune function as length and intensity of exercise [3]. Therefore, unsurprisingly, heavy exercise alone doesn’t suppress immune function but has been proven to be additive to depressed immune systems. In addition, when studying the frequency of exercise, it seems to show a linear effect (more days of exercise, less respiratory illnesses). A study comparing upper respiratory infections vs. average days of physical activity per week showed a 46% decrease in infections in the 5 day a week exercisers as compared to the mostly sedentary group [2]. The effects of more than 5 day a week was not looked at in this study, but I’d assume, based off the above J-curve theory and just personal experience, there would be a point of diminishing returns. Never underestimate the power of true rest days, if you are and everyday type exerciser already and have kept that up.

As a good rule of thumb, exercise physiologist Alex Hutchinson recommends sticking to “60 minutes or less at an average heart rate of 60 percent of your maximum. Inserting some more intense surges is fine; its sustained intensity that seems to tax the body most” [3]. This is the average rule of thumb here. We encourage you to take inventory of your exercise habits (especially as compared to YOUR normal) and adjust from there. But Hutchinson’s words ring true for the majority of us. Embrace the power of the miracle pill of exercise, in the proper dosage

Bottom line, get out there and exercise, a moderate amount will do. Your immune system depends on it. In the words of Earl of Derby, “Those who don’t find time for exercise, will sooner or later need to make time for illness.”

FF Jackie Fehr, Dispatch, B shift

Questions, comments, concerns? Please contact FF Jackie Fehr via email. I’d love to discuss any of the information above and help you find a healthy and sustainable exercise routine that fits your lifestyle.


  1. “How to Boost Your Immune System.” Harvard Health Publishing – Harvard Medical School. https://www.health.harvard.edu/staying-healthy/how-to-boost-your-immune-system
  2. “The compelling link between physical activity and the body’s defense system.” David Nemin and Laurel Wentz. Journal of Sport and Health Science, Vol 8, Issue 3, pgs 201-217. https://www.sciencedirect.com/science/article/pii/S2095254618301005
  3. “What’s the Best Way to Exercise to Maintain a Strong Immune System.” Alex Hutchinson. The Glove and Mail. https://www.theglobeandmail.com/life/health-and-fitness/article-whats-the-best-way-to-exercise-to-maintain-a-strong-immune-system/

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