How Exercise Affects Our Immune System: Facts and Theories
Exercise and the Immune System
Exercise can be a great way to improve the activity of our immune system and reduce the risk of disease. The system constantly protects us from dangers, but it works better under some conditions than others. Its job is to attack and destroy cells and particles that can damage our body and make us ill. Researchers have found that regular, moderate exercise improves immunity. They are still investigating how it does this. Some facts are known, but other ideas are possibilities.
The immune system protects us from pathogens, or microbes that can cause disease. We inhale potentially dangerous viruses, bacteria, and fungal spores. We also eat them in our food. Some pathogens enter the body through other openings. Keeping the immune system healthy is important at any stage of life, but it's especially so in our later years when the system often needs some help and the risk of certain diseases and infections increases.
An Impressive and Complex System
The human immune system is an amazing and complex network of cells, chemicals, and processes. Discovering how the system works is a very active area of scientific research, since the system is so important in preserving our lives.
Researchers have discovered that exercise has significant effects on immunity. These effects are usually beneficial but are sometimes harmful. Moderate exercise performed regularly helps the immune system to function better while intense exercise may hinder its function.
Since scientific reports describe how exercise affects specific components of the immune system, it's helpful to know a little bit about these components. White blood cells are a major part of the system. Some are phagocytes. These engulf and destroy pathogens in a process called phagocytosis.
The Five Types of White Blood Cells (or Leukocytes)
Destroy microbes by phagocytosis (surrounding and engulfing the microbe)
Neutrophils are the most abundant white blood cell.
Have multiple functions, including killing parasites
Eosinophils become more abundant during allergic reactions.
Release histamine and heparin (an anticoagulant) to stimulate inflammation and blood flow in a damaged area
The increased blood flow during inflammation helps heal damage, but basophils may also be involved in allergies and asthma.
Attack invaders directly, help other cells attack, or make antibodies, depending on the type
Three types of lymphoctes are B cells, T cells, and natural killer (NK) cells.
May become macrophages, which destroy bacteria and dead cells by phagocytosis, or dendritic cells, which help other components of the immune system do their job
Monocytes are the largest white blood cell.
It's very important that a newcomer to exercise begins their fitness program with gentle sessions. The duration and intensity of the sessions should be increased gradually. Anyone who is very overweight or who has a serious health problem should seek their doctor's advice before starting an exercise program.
Moderate Versus Intense Exercise
Researchers are examining the effects of single exercise sessions on the immune system as well as the effects of regular ones. They are also taking into account whether the sessions are moderate or intense.
A moderate exercise session is considered to be one that causes the participant to be mildly out of breath and to sweat lightly. An intense or vigorous exercise causes the participant to breathe hard and sweat heavily. In general, health agencies recommend that people get a total of 150 minutes of moderate exercise each week. The total time should be cumulative instead of being completed all at once. 30 minutes of exercise on five days of the week is often recommended.
Types of Exercise for Improving Immunity
Someone trying to improve their fitness level may choose only one type of exercise or alternate between several types. Examples of good exercise choices include walking, running, cycling, swimming, dancing, inline skating, fitness classes, and many types of sports. Some people might like to incorporate exercise into their daily life, such as by walking or cycling all or part of the way to work, school, stores, and appointments. An exercise routine that's enjoyable is more likely to be maintained.
Anyone starting a fitness program should check whether warm-up or cool-down exercises are required for their chosen workouts and whether stretching and/or strength training are advisable.
Health experts say that any form of exercise—even a slow walk—is better than none at all. For the best results with respect to health and immunity, however, the exercise should involve a moderate degree of effort. For example, a walker should walk briskly or uphill, either continuously or in intervals (provided this is safe for their current state of health) in order to increase the intensity of their workout.
Everyone should judge for themselves how a particular exercise routine is affecting their body. If a routine is causing pain or exhaustion, it should be modified and/or professional advice sought.
Effects of Moderate Exercise on the Immune System
Although the relationship between immunity and moderate exercise isn't always clear and isn't completely understood, some interesting discoveries are being made.
- In mice and humans, regular, moderate exercise reduces the risk of colds and flu compared to the risk in sedentary mice or humans. Any cases of flu that do develop in the individuals that exercise are relatively mild.
- After a moderate workout, the concentration of macrophages in the blood increases temporarily. A similar observation has been made for the concentration of lymphocytes in the blood.
- During exercise, there is an increased rate of blood flow in the body. The blood contains agents of the immune system.
- Regular, moderate exercise generally helps us to lose weight if we need to and helps us to maintain a weight that is healthy for our body. Being overweight hinders the immune system.
- Exercise also helps us to get a good night's sleep. Lack of sleep depresses immunity.
- In addition, exercise reduces stress. Chronic stress has a negative effect on immunity.
Possible Effects of Exercise on Immunity
The U.S. National Library of Medicine lists some other possible ways in which exercise may help the immune system. As they say in the reference at the end of this article, the ideas haven't been proven, but they are interesting to consider.
The organization says that exercise may "flush" bacteria out of the lungs and airways. They acknowledge that exercise causes changes in white blood cells and in the antibodies produced by some of them. Both items travel through the circulatory system more often during exercise. Although it may sound logical that this is helpful, we can't assume that it is without studies that prove it.
The organization also notes that we experience a short rise in temperature during and after exercise, which may help the body to fight an infection better. It's known that this happens when we have a fever. The mechanism for the latter observation is still being investigated. Some British scientists have found that a moderate fever appears to affect certain proteins in the body and the genes that they control in a beneficial way.
The observation described above doesn't mean that a high fever should be ignored when we're sick. There is a point at which a fever changes from helping the body to hurting it. If anyone has questions about the point at which a fever should be treated, they should consult a health professional.
Possible Detrimental Effects of Strenuous Workouts
Strenuous exercise appears to be less beneficial for the immune system than moderate exercise.
- In mice, repeated periods of long and intense exercise lead to an increased rate of colds and flu compared to the risk in moderate exercisers and sedentary individuals. In addition, the infections are more severe in the mice that exercise strenuously.
- In humans, after a long and strenuous workout the activity of neutrophils, monocytes, and lymphocytes is temporarily depressed and they behave less effectively. When a lymphocyte encounters an invader it normally multiplies rapidly, a process known as lymphocyte proliferation. This process is reduced after a prolonged exercise session, especially in one that lasts at least one and a half hours and is performed at moderate to high intensity.
- In addition to the immune system changes described above, researchers have noticed that the concentration of NK cells is decreased as well. There are also changes in the levels of specific chemicals in the immune system.
- David Nieman, a scientist and runner, has found that people who participate in a marathon (just over twenty-six miles in length) have a depressed immune system for hours to days after the event or after an intense training session. Observational studies suggest that the runners have an increased risk of getting sick during this time period.
- It's been observed that some of the immune system changes noticed after heavy exercise are prevented if carbohydrate is ingested during the exercise.
Some Discoveries May Be Misleading
Although a long and intense exercise session seems to temporarily increase the risk of a person getting sick, the infections that develop tend to be upper respiratory tract infections and generally aren't serious. In addition, in some people exhibiting symptoms of a respiratory tract infection after strenuous exercise, no infectious agent has been found. It's been suggested that the "infections" in these people are actually caused by increased exposure to airborne allergens and irritants.
In most people, the benefits of become fitter, stronger, and leaner from repeated and prolonged periods of strenuous exercise are considered to outweigh the disadvantage of a temporary susceptibility to a respiratory infection. The infections may be more bothersome for elite athletes who train rigorously for a long period of time. It's not a good idea for anyone to exercise to exhaustion, however. In addition, intense exercise increases the risk of injury.
It should be noted that in 2018 researchers at the University of Bath published a report claiming that some of the negative observations about strenuous exercise on the immune system were misleading. (The report is referenced below.) For example, the researchers say that although the level of certain immune cells may decrease in some parts of the body after strenuous exercise, the change may actually be helpful. The scientists say that instead of being destroyed, the cells are moving to other parts of the body where they may be needed.
A person may need to judge for themselves how strenuous or endurance-type exercise affects their personal susceptibility to infection, assuming they want to exercise in this way.
Other Factors That Can Help the Immune System
Though the ways in which exercise affects the immune system and the different effects of moderate and intense exercise on the system are still being investigated, researchers agree that moderate exercise is good for us and our immune system (except in the case of people with people with certain health problems, who should seek their doctor's advice).
There are other things that we can do to help our immune system in addition to getting appropriate exercise. These including eating a healthy diet that is filled with beneficial nutrients and is low in sugar, salt, and the less healthy fats, getting enough sleep, reducing stress, and avoiding smoking and excessive alcohol intake.
Helping the immune system stay in top condition is very important for preventing or weakening both minor and more serious illnesses. Boosting immunity when necessary can improve both our health and our quality of life.
- Moderate and Vigorous Exercise: Information about the differences from the National Health Service
- Exercise and Immunity: Information from the National Library of Medicine
- Sport, Exercise, and the Immune System: A detailed look at the effect of exercise on the immune system from the American Physiological Society
- Marathon Training and Immunity: Immune system changes during marathon training from PubMed and the U.S. National Library of Medicine
- The Elite Athlete Paradox: Repeated intense exercise builds fitness but increases susceptibility to infection from The Guardian newspaper
- Strenous exercise may not suppress the immune system from the University of Bath
- How a fever helps the immune system from Medical News Today
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
© 2012 Linda Crampton