You’ve long known that physical activity benefits your overall health. However, precisely what impact regular exercise has on the immune system remains unclear despite vigorous research.
One fact appears indisputable from the existing research — moderate exercise reduces your risk of everything from upper respiratory infections to cancer. However, what qualifies as “moderate” exercise? What type of workout is best, and how often should you sweat it up?
The waters become even murkier when you ask how intense exercise affects the immune system. Is too much of a good thing harmful to your health? How do factors such as your gender, age and previous fitness level affect the results?
Understanding what science knows to date helps you make more informed decisions for managing your health. Exploring the effect regular exercise has on the immune system may inspire the perfect routine to see you through the next cold and flu season.
Regular, moderate exercise appears to benefit immune function. Multiple studies have examined the effects of working out on various components and found that sweating it up changes everything from how your genes express themselves to how your body manages inflammation.
You may mistakenly believe inflammation is a bad thing, and too much of it is. However, inflammation also plays a crucial role in your body’s immune response. For example, blood and various immune cells race to duty when you twist your ankle, producing red heat that also cushions the affected area to protect it from further injury while delivering healing oxygen and nutrients.
Inflammation is problematic when it becomes systemic and fails to function as intended. For example, systemic inflammation increases the symptoms of various chronic diseases, such as rheumatoid arthritis. Many people who died from COVID-19 perished from cytokine storms. These occur when inflammation damages multiple organs as the immune system overreacts to a perceived threat.
Regular, moderate exercise may mitigate your body’s inflammatory response. Initially, exercise increases short-term inflammation, but in moderate exercisers, levels quickly decrease. The impact of intense, long-term exercise on the immune system is murkier.
Part of exercise’s impact on your immune system may lie in how it impacts your genes. Epigenetics is how genes express themselves over time — which ones “switch on” and “off” and when.
A recent study from Stanford found that exercise altered the expression of 22 genes in all six tissue types studied. These changes included shifts in the expression of several genes implicated in Type 2 diabetes, heart disease, obesity and kidney disease. This research lends hope if you have a history of such conditions in your family — you may not be as much of a victim of your DNA as you fear.
Considerable controversy exists as to how much exercise and what type you need to improve your immune response sufficiently to ward off acute illnesses, such as upper respiratory infections like COVID-19. Debate continues as studies produce inconsistent results.
For example, one recent narrative review of multiple studies showed that exercise changes the function of various immune system components like natural killer cells, neutrophils, pro-inflammatory cytokines and T and B lymphocytes. It also affected levels of different inflammatory markers, including several interleukin factors, TNF-alpha and nuclear factor kappa.
While the review demonstrated that strenuous and moderate-intensity exercise had different impacts on the immune system, what qualifies as moderate remains unclear. Furthermore, several competing factors weren’t included in every study, such as the age and overall fitness level of participants, their gender, nutrient intake, average stress level and socioeconomic condition.
Multiple factors interplay to determine precisely how exercise affects immunity. For example, those who consume a diet high in omega-3s may have lower levels of inflammation thanks to their food intake as much as their activity. Failure to account for such factors produces inconsistent study results.
Both moderate and strenuous exercise increases the number of several key immune cells, such as natural killer cells. Moderate exercise appears to release both pro- and anti-inflammatory cytokines, mitigating inflammation levels. Strenuous exercise, conversely, reduces glutamine availability, a crucial amino acid found in your muscles, and increases dry mucosa, increasing the risk of upper respiratory infection.
One study reveals why levels of certain immune cells increase with regular, moderate exercise. Researchers from York University found that moderate exercise altered how cells in your bone marrow breathe, creating and training the precursors of macrophages. These immune cells seek and destroy foreign invaders. Such changes appeared up to a week after exercising, not only in its immediate aftermath.
The immune-boosting effects of regular, moderate exercise may extend to cancer prevention. One study by researchers at the MD Anderson Cancer Center at the University of Texas found that regular aerobic exercise may reduce colon cancer risk in men with Lynch Syndrome (LS). LS is a hereditary condition that results in a 60% to 80% chance of colorectal cancer development in men and 40% to 60% in women.
Another recent trial run by Jens Hillengas, MD, PhD, of the Roswell Park Comprehensive Cancer Center, showed that exercise may strengthen the immune system of those with multiple myeloma. This blood cancer occurs when plasma cells grow out of control. Those engaging in six months of physical activity consisting of strength training or walking showed that the exercise group had a greater number of non-exhausted T-cells capable of fighting cancer.
While moderate exercise appears to benefit immune function, the beneficial effects become less clear when intensity increases. Intense physical activity increases the level of oxidative stress in the body, which one recent study suggests may increase your susceptibility to infection, especially immediately following intense bouts.
Other immune system changes may also make you more susceptible to infection after intense exercise. One recent study found a reduced number of inflammatory molecules following extreme exertion, implying that your body may have fewer reserves left to battle germs.
Working out hard means heavy breathing, and researchers also found changes in your oral microbiome that may affect your infection risk. They hypothesize that intense activity may reduce respiratory tract inflammation to aid breathing, leaving your body more susceptible to invading germs.
Age and previous fitness levels may influence exercise’s impact on your overall immune health. A study performed on 32 physically active men showed that older adults had a more favorable increase in lymphocyte count immediately after strenuous exercise. At the same time, overall fitness ability did not affect immunological markers.
Likewise, exercise intensity may impact women differently than men. A recent review in the European Medical Journal shows that while moderate exercise improves immune function regardless of sex, high-intensity exercise impairs the immune response more severely in females than in males.
The overarching consensus is that regular, moderate exercise has a beneficial impact on the immune system. The question becomes, what is “moderate?”
Exercise physiologists have several measures to define exercise intensity. In many cases, the most accurate answer comes from combining METS with your V02 max.
METS stands for metabolic equivalents and is based on a METS score at one while at rest. Other activities receive varying scores — for example, a brisk walk is 5.0 METS, while walking the dog is 3.5. However, various factors affect METS, including:
For example, the same walk may require more exertion from a 60-year-old obese individual than one who is 20 and of average weight. For the most precise measure, many professionals rely on the V02 max to address factors like your cardiovascular fitness level.
Your VO2 max measures how well your body uses oxygen. The only accurate way to measure it is through a laboratory test, although certain standardized measures like the Bruce treadmill test can give you a decent idea.
How does it come together? In general, health professionals define moderate-intensity exercise as that ranging between 3 and 6 METS. However, some such activities might qualify as vigorous for certain individuals. To stay within moderate range, you can use one of the following three self-tests to determine your exercise intensity:
According to the World Health Organization, you should get between 150 and 300 minutes of moderate activity per week. However, a recent study suggests that those who aim for 300 or above see even greater health benefits in terms of overall longevity.
The bottom line? Move more often to benefit your health — just don’t necessarily go hard.
The good news is that breaking your exercise up into smaller segments has equivalent benefits to a single long session. Shorter sessions may even be superior for mitigating oxidative stress loads and making it more manageable to fit movement into your lifestyle. Many people find the following activities moderate in intensity and easy to do in the time they have available:
Science has long known that physical activity benefits you. The impact of regular exercise on the immune system has remained unclear, although recent studies indicate several ways it can boost your health. It increases the number of vital killer cells and modulates inflammation to keep it working as intended.
However, intense exercise may affect the immune system negatively, at least in the short term. Moderation appears best for reaping the benefits of physical activity to decrease your chances of everything from COVID-19 to cancer.
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