EXERCISE AND IMMUNITY: 7 WAYS HOW EXERCISE CAN HELP YOU THIS FLU SEASON

Medically Reviewed by Dr. Rosmy Barrios - September 18, 2024

Would it surprise you to know that exercising regularly can do more for your immune system than any supplement or therapy available on the shelf?

The immune-enhancing benefits of exercise allude to just how vital it is for us to engage in physical activity on a regular basis. These benefits go way beyond keeping in shape, lending themselves to preventing disease onset, promoting longevity, and reducing our chances of catching COVID.

The following article highlights how our state of health reflects in our ability to move our bodies. Ways in which physical activity affects our immune system are discussed below, along with tips for making the most of exercise.

Exercise Supports All Aspects of Our Physiology

Keep in mind that the body is designed to move and that exercise is required for everyday functioning. It should not be viewed as a laborious health prescription but rather as an enjoyable recreational necessity that adds to your quality of life.

Most people know about the cardiovascular benefits of exercise. In reality, it supports every single tissue, organ, and system of the body with profound effects on metabolism. When we move our bodies, every cell also experiences movement – the movement of fluids, nutrients, energy particles, cellular products, waste, communication signals, and more. By strengthening the muscles, nerves, blood vessels, organs, and bones, as well as increasing available energy and nutrient supplies, most cellular processes are optimized.

The immune system is no exception, spanning all white blood cells, the thymus gland, and the innate defenses of all cell types. In this regard, it is difficult to say whether exercise directly improves immune function or indirectly benefits the immune system by supporting our overall health.

7 Ways Exercise Can Boost Immune Function

In the absence of malnourishment, consistent moderate-intensity exercise is associated with the below immune boosting benefits: 

1. Protects Against Respiratory Infections, Including COVID-19

Exercise is well-known to lower the risk for contracting respiratory infections, largely due to enhancing overall immune function. Recent studies are now showing how exercise may indirectly offer further protection against respiratory infections:

COVID. Since the beginning of the COVID outbreak, health experts have been urging the public to exercise as a generalized immune-enhancing protective measure. Reviews 1 year into the pandemic show that those who exercise frequently were less likely to contract the virus^{[1] [2]}. In vitro studies have shown that exercise can reduce blood pressure by transiently decreasing the expression of ACE2 receptors and enzymes that the virus uses for cellular infiltration.^[3] In those previously exposed, exercise improved immune cell recognition, action, and antibody production in response to the virus.^[4] Aside from these benefits, exercise is protective against the potential adverse effects of other prevention measures, including social isolation^[5].

Influenza. Regular exercise was shown to protect the elderly against contracting influenza by enhancing antibody responses to the influenza vaccine^[6]. Further research is required to clarify if exercise decreases one’s inherent susceptibility to contracting the flu. However, those who exercise report fewer respiratory symptoms over a year, which suggests that they contract the flu less often than those who are sedentary^[7]. Frequent physical activity is known to lower symptom severity, reduce damage post-infection, decrease time spent sick, and protect against flu-related mortality^[8].

Other Respiratory Infections. Results concerning the preventive effects of exercise for other respiratory infections are conflicting. In one trial, those who exercised frequently displayed a 16% reduction in general respiratory infectivity rates over an 8-week period than those who did not exercise.^[9] A more extensive review showed no association between regular exercise and infectivity rates. However, it did reveal that exercise reduced symptom severity and the number of days spent ill.^[10]

2. Reduces Illness Severity

Aside from enhancing immunity and reducing the risk for contracting various infections, consistent exercise is known to reduce the severity of infections and other diseases:

Lowers Overall Disease Risk. The all-rounded effects of regular exercise on the body protect against all forms of disease. Moderate exercising improves the function of the heart, respiratory system, immune system and overall metabolism. These combined effects are known to lower the risk of cardiovascular disease and metabolic conditions such as diabetes. Maintaining the muscles and bones through frequent exercise also helps to keep the body strong, which lowers the risk of contracting musculoskeletal disorders, chronic pain disorders, and chronic fatigue. Evidence also suggests that exercise may improve immune function in cancer patients receiving chemotherapy^[11].

More Tolerable Symptoms. A few studies highlight that those who participate in regular moderate exercise experience less intense symptoms due to disease or infections. Exercising serves to regulate the immune system and metabolism, thereby helping to reduce pain perception and inflammation (associated with symptoms severity). Concerning COVID-19, exercise may be able to reduce the risk of lung damage induced by SARS-COV2 through regulating the angiotensin II pathway and lowering blood pressure^[12].

Less Time Sick. Compared to those who lead a sedentary lifestyle, those who exercise frequently spend an average of 40-50% less time ill when suffering from a respiratory infection. This result greatly outcompetes any medications and supplements one could take to treat or protect against infectious symptoms.

Pro-Longevity. Those who lead a physically active lifestyle are known to have a ±30-35% lower risk for all-cause mortality than those with a sedentary lifestyle. This roughly translates to a lifespan of up to 5 extra years for those with a history of lifelong physical activity and improved quality of life during old age. Former athletes in sports involving aerobic endurance exercise were shown to live longer than other types of athletes.^[13]

3. Enhances Adaptive Immune Responses

Increases White Blood Cell Count and Distribution. Exercise is known to stimulate the production of healthy, robust white blood cells from both the thymus and bone marrow. After exercise, blood levels rise for several hours before diminishing. The reductions are attributed to the enhanced distribution of white blood cells^[14] and can serve to lower low-grade vascular inflammation perpetuated by faulty immune cells^[15]. Exercise enhances blood circulation, allowing for an even dispersion of white blood cells throughout all tissues of the body. This naturally improves surveillance and protection of all tissues.

Immune Cell ‘Memory’ and Surveillance. Some studies indicate that exercise enhances the ability of immune cells to detect foreign material, as well as their ability to mount defenses against known threats. In athletes, lifelong exercise at high intensity was associated with increased white blood cell diversity, which improves the range for threat detection amongst immune cells.^[16] Other studies show that compared to men who are sedentary, older men who exercise moderately display an increased number of memory T cells (those that remember a specific threat) that have a longer lifespan (longer telomere length).^[17]

Antibody Production and Vaccine Efficacy. As highlighted above, exercise has been shown to enhance antibody production in response to vaccination. Participants who exercise regularly and those who had exercised just before getting an immune shot were shown to have much higher levels of antibodies than those who exercise infrequently. 

4. Facilitates Metabolism, Innate Immune Function, Cell Turnover and Repair

Innate Immune Efficiency. The innate immune system is an inherent component of all cells in the body. It works with and within the adaptive immune system to protect the body from threats. Exercise stimulates and regulates innate immune responses, which improves cellular defenses, cell-to-cell communication, and promotes the body’s natural mechanisms for regeneration and repair^[18]. This is due to the way in which exercise regulates metabolism.

Metabolism Predicts Immunity. At the cellular level, unbalanced metabolic signaling often interferes with the immune system in ways similar to an infection (known to induce similar pro-inflammatory chemistry). This is due to the nature of pathogenic bacteria and viruses, which either interfere with or hijack metabolic pathways in order to live in the body. Common pathways that are affected involve the basic cellular utilization of fats, proteins, and glucose. Hence, abhorrent metabolic signaling, from either disease, infection, lifestyle factors, environment, or diet, is known to unbalance the innate immune function and promote the incidence of disease.

Metabolic Regulation. Exercise serves to regulate these common pathways by forcing cells to shift metabolism, adapt to physical activity, and build muscle. As a result, excessive fat and glycogen stores are used for tissue maintenance (vs. hindering cellular processes), nutrients and fluids are recycled, and any cells that cannot accommodate the process are eliminated or repaired.

5. Delays Aging of the Immune System

It seems that the fitter one is and the more exercise one can comfortably enjoy regularly, the better their immune function throughout life^[19]. The below points highlight aspects of immunity that are improved in older individuals who exercise regularly.

Protects Against Thymic Involution. Regular, moderate-intensity exercise was shown to help maintain the mass of the thymus gland, which deteriorates with age.

Improves Immune Cell Turnover. Exercise encourages the generation of young, healthy immune cells while promoting the turnover (death) of faulty aged immune cells.^[20] These results were shown to be exercise dose-dependent.

Boosts function of aged immune cells. Exercise in elderly individuals has been shown to boost immune functions by promoting better distribution and function of immune cells. Factors that suppress the immune system were shown to decrease post-exercise, indirectly enhancing immune function. Immune cells in the physically active elderly tended to respond more accurately to immune signals. They were thus better able to coordinate a response than those seen in sedentary counterparts. Some studies report that exercise helped improve the phagocytic ability of monocytes and neutrophils, thereby enhancing cellular repair and innate antimicrobial mechanisms.

Increases the lifespan of functional immune cells. Some studies highlight how exercise in older individuals lengthens the lifespan of healthy immune cells.^[21]

6. Helps to Regulate Inflammation

Inflammation is often spoken of as a negative aspect of immune function. While this is true in many cases, inflammation is a primary requirement for optimal immunity and general metabolism. Inflammation needs to be kept in balance, as too much or too little is known to induce health problems if sustained for too long. This demands a balance of anti- and pro- inflammatory cell signals that fall within the spectrum of health under any given context.

Pro-Inflammatory Actions. There are multiple aspects of exercise that contribute to the regulation of bodily inflammation. With respect to cell turnover, exercise can increase inflammation in order to eliminate old cells, stimulate new growth, and expel unwanted elements from older tissues. If done in moderation, this type of pro-inflammatory activity is required for a balanced metabolism, keeping the anti-inflammatory side of immune function in check.

Disrupting Cycles of Low-Grade Inflammation. In states of disease, chronic low-grade inflammation tends to be expressed in a pattern unique to the condition. Inflammatory markers are often increased directly after exercise yet dip down to healthy levels post-recovery. In so doing, exercise at the right intensity and duration can promote the absence of chronic low-grade inflammation through both pro- and anti-inflammatory mechanisms.

Anti-Inflammatory Actions. Exercise is also known to increase the release of various anti-inflammatory compounds from different tissues, which serve to keep the pro-inflammatory component of immune function balanced. These include:

• Myokines. Muscle-derived cytokines (immune signals pertaining to inflammation) have been shown to exert anti-inflammatory effects on immune cells and surrounding tissues. This is due to the way in which they stimulate the release of anti-inflammatory cytokines. Muscles release myokines in larger quantities during exercise. Myokines have also proven to protect against metabolic diseases by beneficially supporting optimal glucose and fat metabolism. In the long term, it is theorized that myokines released after exercise can improve glucose tolerance and help reduce unwanted body fat.^[22]
• Endorphins. Exercising is well-known for releasing endorphins that reduce inflammation and the associated pain. Endorphins may also improve the ability of lymphocytes to divide^[23], thereby enhancing their ability to tackle a known problem.

Fat Burning. Excessive fat stores eventually lead to the accumulation of pro-inflammatory immune cells (e.g. M2 macrophages), which promote chronic low-grade inflammation, as seen in those with obesity. As exercise supports fat burning, muscle building, and cell turnover, it indirectly regulates this type of inflammation by reducing the accumulation of faulty immune cells in fatty tissues.

7. Promotes Positive Cellular Signaling

Neuro-Endocrine Regulation. Exercise appears to regulate the release of most major neurotransmitters and some hormones, including serotonin, catecholamine, and adrenaline^[24]. This, in turn, stimulates immune cell mobilization and may be responsible for the enhanced immune responses seen after bouts of moderate-intensity exercise.

Mood. Exercise is literally an ‘uplifting’ experience for the whole body. The way in which exercise serves to regulate neurotransmitters, hormones, and the immune system has a positive effect on our mood and vice versa^[25]. A balanced good mood is associated with better immune function and lower rates of disease.^{[26] [27]}

Sleep. Day-time exercise has been shown to help regulate the nervous system in a way that promotes better quality of night-time sleep^[28]. Sleep and immune function are intimately connected. Good quality sleep is conducive to regulating immune function and reducing inflammation, whereas sleep deprivation is associated with disease onset.^[29]

Lessens Pain Intensity. The sensation of pain comprises a series of neuronal networks found in both the brain and body. Exercise can lower pain perception by stimulating the brain in a positive way, promoting new neuronal growth in both brain and muscle tissue, and regulating metabolic pathways. This can lessen the intensity that is often enhanced by pre-established neuronal networks associated with pain. Furthermore, some anti-inflammatory compounds released during exercise, such as endorphins, serve to block pain.

Gut Microbiome. The gut microbiome is considered as one of the largest organs in the body, housing trillions of bacteria. It exerts profound influences on our immune system and serves as a primary wall of defense. Moderate exercise is known to help improve gut function, aiding with digestion and lowering stool transit time. This helps reduce potential pathogenic interactions in the gut and improves immune function by increasing nutritional availability. Interestingly, exercise in the absence of starvation appears to benefit gut microbe diversity by enhancing the ratio of good gut bacteria.^[30]

When Exercise is a Bad Thing: Side Effects and Contraindications

Exercise can exert both pro- and anti- inflammatory effects on the body, which can cause the immune system to become unbalanced if excessive.

Everyone Responds Uniquely to Exercise. More research is required to clarify when exercise can be damaging to health. It is understood that the outcome depends largely on the individual in question. Personal factors such as metabolism, the length, type, and intensity of the exercise, as well as genetic and environmental factors (i.e. stress, nutrition, sleep, general health, etc) are known to play a role in the result. Yet, the combined extent to which these factors can affect one is unknown and variable.^[31]

Side Effects of Over Exercising. Nonetheless, excessive exercise is seen to induce the following effects in susceptible individuals:

• Immune Suppression. It is well documented that periods of intensive training for sports events serve to increase the risk for respiratory infections (alongside other stressors) in professional athletes. Prolonged intensive exercise may suppress several immune cells and their functions, including T-lymphocytes, natural killer cells, and neutrophils. Excessive exercise was shown to inhibit allergic responses, detection of pathogenic material, and production of antibodies (especially IgA) in some individuals.^[32]
• Immune Hyperactivity. Compared to frequent long-term intensive exercise, single bouts of overexertion may promote severe exhaustion, heightened immune responses, excessive muscle breakdown, and widespread inflammation, all of which detract from the benefits of regular physical activity.
• Injury Risk. The more one exerts oneself, the higher the risk for injury. This is particularly true of repetitive exercises and activities in which one part of the body is placed under continuous mechanical stress. Those working in highly competitive physical professions, such as dance or gymnastics, often end up suffering from musculoskeletal disorders and chronic injuries later in their careers.

Risks that accompany exercising can be partially reduced by leading a healthier lifestyle in other spheres of life. This includes eating a balanced, nutritious diet, getting enough sleep and sunlight, keeping hydrated, minimizing stress, and resting when required.

Exercise Contraindications. As a general rule, you should not engage in strenuous physical activity:

• While fighting an active infection.
• During the early recovery phase after an injury, surgery, or an equally traumatic event.
• When your immune function is severely compromised.
• If severely malnourished.
• If you suffer from Mast Cell Activation Syndrome.

Most of the above situations are temporary. In order to recover properly from most of the above conditions, exercise ought to be gradually re-instituted after an initial intensive recovery phase. Mast Cell Activation Syndrome is an exception, as exercising can be potentially fatal to those with the condition.

How Much and What Type of Exercise is Optimal?

Research shows that regular exercise at a moderate intensity is beneficial for health. In contrast, long spurts of intensive exercise can suppress immune function, promote fatigue and increase the risk of injury.

Weekly Recommendation. The general recommendation is to exercise at a moderate intensity for a minimum of 150 mins over a week. However, recent studies have highlighted that this recommendation is not appropriate for everyone. For instance, South Asians may only show similar benefits when engaging in 266 mins of moderate-intensity exercise per week. Thus, you may need to adjust your exercise routine depending on your genetics, energy requirements, and metabolism.

Exercise Duration. Most studies have focused on the benefits of moderate-intensity exercise for durations of 30-60 mins at a time. Exercising for more than 2 hours at a time is associated with fatigue and negative changes in immune function, especially if one is not accustomed to this degree of physical activity.

Types of Exercise. The type of exercise you do is perhaps more important than how much you can do per week. It’s essential to incorporate a variety of exercises to strengthen all areas of your body. Aside from improving health and well-being substantially, variation in your routine helps to keep it interesting and encourages consistent physical activity.

Important examples of exercise types include:

• Aerobic and endurance exercise
• Stretching
• Weight Bearing
• Strength and Resistance Training
• Coordination Exercises

Many enjoyable forms of exercise, such as sports or dance, encompass several of the above exercise types, adding to their benefit. They are also typically goal-oriented, which makes them more fulfilling to pursue.

Making the Most of Exercise

The benefits of exercise are greatly enhanced when one leads a healthy lifestyle. This demands getting sufficient nutrition, sleep, and sunlight, as well as balancing work with time out. When these factors are balanced, the risks of exercising are diminished.

Post-exercise, the following aspects are important to keep in mind for maintaining balanced immune function:

• Carbohydrates after exercise have been shown to lessen the impact of strenuous activity by replenishing glucose stores, reducing stress-related hormone levels (e.g. adrenaline), and decreasing inflammatory activity.^[33] While this extends to all carbohydrates, nutrient-dense carbohydrates (i.e. fruits and vegetables) are known to be far more effective than refined carbs high in sugar for post-workout recovery and immune function.
• Proteins can enhance muscle building when moderately consumed before or after exercise. Make sure your choice of protein is easy to digest or combined with a source of water-soluble (prebiotic) fiber.
• Hydration. It’s vital to keep hydrated, particularly when breaking a sweat. Moderate to high-intensity exercise is known to induce temporary dehydration. Taking small sips of water throughout and after working out is more beneficial than drinking large volumes in one shot. Purified mineralized water is best for optimal hydration.

Conclusion

No matter your age, exercise is a necessary component of physical well-being. By working your body, you are actively boosting your metabolism and promoting overall health. The immune system similarly responds to exercise by revving up on all its processes, including tissue surveillance, problem resolution, and regeneration. Moderate exercise serves to regulate immune function in people of all ages and helps to protect against a variety of diseases and infections, such as CVD, diabetes, and COVID-19. So rather than worrying about getting sick and growing old, why not break a sweat instead?

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