In direct — increasing white blood cells — and indirect — increasing blood flow — ways, exercise improves your immune system. As researchers of a comprehensive literature review write, “Different studies suggest that regular physical exercise is directly related to decreased mortality from pneumonia and influenza, improvements in cardiorespiratory function, vaccine response, metabolism of glucose, lipids and insulin.” Learn how exercise and immune system health are related as well as seven ways aerobic and resistance training, performed on a regular basis with proper rest and recovery, can improve how your body responds to threats. 

Normal exercise improves overall immune function

Moderate-intensity physical activity decreases inflammatory responses and stress hormones while increasing several types of white blood cells. Exercise prepares the body to battle the inflammatory cells produced by pathogens as it has already raised the immune defenses. White blood cell concentration peaks 30 minutes to two hours after exercising and persists for up to 24 hours. 

Cardio exercise in particular stimulates immune cells in the respiratory tract, which improves antiviral response in these areas where pathogens enter the body. As researchers claim, “Regular exercise of moderate intensity has already been associated with a reduction in respiratory infections compared to sedentariness.”

On the flip side, too much exercise without proper rest can deplete the immune system. Overly strenuous exercise before or after a viral infection, like the flu, can prolong or exacerbate the illness. It’s not just in times surrounding illness; overtraining (excessive exercise without rest and recovery) in general has a negative effect on the immune system. When you exercise, the body produces anti-inflammatory proteins to repair muscles, but in excessive physical activity, it can suppress the immune system and leave you vulnerable to infection. This makes avoiding overtraining even more important. While regular exercise improves immune function, prolonged, high-intensity exercise without proper rest and recovery decreases immunity.

Exercise increases immune response to vaccines

Numerous studies demonstrate enhanced antibody response when exercise is performed prior to vaccination. Researches tested the COVID-19 and flu shots. People who exercised in close proximity to receiving vaccines had increased antibodies to each vaccine four weeks after immunization. Exercise did not increase side effects of any of the vaccines. Researchers extrapolate from the results, “These findings suggest that adults who exercise regularly may increase antibody response to influenza or COVID-19 vaccine by performing a single session of light- to moderate-intensity exercise post-immunization.” One explanation is that exercise acts as an “acute stressor,” and acute stress prior to vaccination may enhance immune response.

Exercise lessens inflammatory markers

As functional medicine practitioner Dr. Will Cole writes in The Inflammation Spectrum, “When you dive deep into just about every health problem that we face in the world today — anxiety, depression, fatigue, digestive problems, hormone imbalances, diabetes, heart disease, or autoimmune conditions — they are all inflammatory in nature or have an inflammatory component.” Just 20 minutes of exercise can produce an anti-inflammatory cellular response. Exercise increases interleukin 6, a protein that supports immune response and is associated with an increase in anti-inflammatory proteins, in proportion to the duration of the activity as well as the muscle mass used in exercise. Researchers say this may be beneficial for the immune response in people with chronic inflammation, which runs rampant and can turn your immune system from protector to attacker. “By the time a health problem is advanced enough to be officially diagnosed, inflammation has typically already caused significant damage to the body,” Dr. Cole writes. 

Exercise increases antioxidants

Resistance training (a broad term for weightlifting and any activity involving moving weight, even when your own bodyweight acts as resistance in movements like pull-ups, lunges, etc.) enhances expression of extracellular superoxide dismutase enzyme, a critical antioxidant that is prevalent in the lungs. It is also shown to lower oxidative stress markers. Indeed, elderly active people have antioxidant activity similar to younger sedentary people.

Oxidation is a normal part of the processes that keep us alive. The problem is when external factors create more oxidation than our natural antioxidant systems can handle. Chronic oxidative stress is implicated in numerous health conditions as it weakens, damages, and can ultimately kill cells. Exercise increases oxygen demand from the muscles, increasing free radical production and oxidative stress, which is a vital part of the process of the body adapting to training, i.e., getting stronger and building muscle. 

However, it’s all about smart training and progressive load. An untrained person who performs 30 consecutive minutes of intense, close-to-maximal exercise can have increased free radical production that limits muscle function. On a regular basis, that can damage and kill cells. That same exercise for 30 minutes at the same intensity performed by someone who has been progressing to that level can have the opposite effect of producing more antioxidants. “Therefore, excessive physical exercise is detrimental to untrained individuals, but progressive training allows the cells to more easily detoxify a larger amount of ROS [reactive oxygen species a.k.a., free radicals],” researchers write.

People who train on a regular basis (not those who binge exercise, performing sporadic bouts of strenuous exercise to exhaustion) accumulate lower levels of free radicals and better protect their bodies from oxidative damage.

Exercise combats immune system suppressor obesity

Obesity gets in the way of the immune response. It is characterized by chronic inflammation and oxidative stress. Obese people have delayed and blunted immune responses to viruses as well as less vaccine efficacy “Through exercise, there is an improvement in the response to infection in obese individuals, due to immune and cellular restoration,” write the authors of an extensive literature review on obesity, exercise, and the immune system.

Exercise supports blood flow

As researchers say, “Blood is the pipeline of the immune system.” Your blood carries immune system cells to where they are needed to fight off threats to your health. Long-term aerobic training is associated with a decrease in blood clotting potential, reducing the risk of blood flow restriction.

Exercise lowers stress

Experts estimate 75–90% of primary care visits are stress related. Chronic stress can suppress your immune system by the constant hormonal stress response as well as increasing risk of obesity, diabetes, cardiovascular diseases, depression, and anxiety. Stress causes sleep disruptions, which further depletes immune function. It also leads to unhealthy behaviors, like overeating/eating junk food and using drugs and alcohol. While scientists are not clear on the exact mechanisms, numerous studies suggest exercise lowers stress. Is it losing yourself in a workout that tells stress to take a time out? Maybe. What has been demonstrated is that the calming effects of exercise last for hours after your heart rate has returned to normal.