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How much do you know about your immune system? Just like any other part of your body, your immune system can be affected by how well you take care of it. 

In recent years, more research is beginning to show that the amount and type of exercise we participate in can influence our immune system.

This article addresses:

  • basic information about how your immune system works
  • how exercise affects the immune system
  • how regular, moderate exercise can provide benefits to your immune system

Introduction to the Immune System
For many of us, the immune system seems like a bit of a mystery. The immune system is large and complex, and performs a wide variety of functions. Scientists and researchers are constantly studying the immune system and making new discoveries.

Some of the factors that influence or affect the daily functioning of your immune system include your age, gender, eating habits, medical status and fitness level.

Did you know that your skin is part of your immune system? Our skin is our first line of defence, acting as a physical barrier to all the things in the world that can do harm to our body and make us sick, such as bacteria and viruses.

White blood cells are another vital part of our immune system. There are many different types of white blood cells that circulate throughout our body, playing different roles and all communicating with one another.

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A lesser known, but equally vital part of our immune system are hormones and cytokines. Hormones and cytokines are important because they help cells communicate and help initiate immune system defences.

We don’t always think about it, but our immune system does a lot of great things every day to keep us in good health. The immune system:

  • fights colds and flu viruses
  • deals with bacteria and viruses we may come in contact with
  • fights “bad” cells that form in our body (e.g., cells that could mutate and be cancerous)

Your Immune System is Smart
The immune system is an amazing thing. When we are healthy, it is in balance. When we get sick, one or more components of the system will grow strong and take charge to fight against whatever is attacking our body, such as a virus or bacteria.

While this defence mechanism happens, other parts of the immune system step back, allowing certain white blood cells, cytokines and other components of the immune system to do their jobs. Eventually, when the infection or problem is gone, the immune system will balance out again.

When your immune system is not in balance, or is not functioning correctly, this is often when health problems can appear. For example, multiple sclerosis and rheumatoid arthritis are considered to be autoimmune disorders, where some part of the immune system may attack some part of your body.

Another example is prolonged inflammation.  Inflammation is a component of the immune system and is considered a response to stress.  When you experience inflammation, it’s an indicator that the immune system is doing its job, by getting the white blood cells and other components of the immune system geared up to work.

Initially, inflammation is usually a good thing. But if the inflammation persists for too long, it can be bad. For example, research is showing how inflammation is associated with chronic diseases, such as heart disease, and with metabolic disorders, such as diabetes.

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Many Factors Influence Immunity
Your immune system is influenced by many things and will change throughout your life span. Immune systems function differently for men and women, and vary from infancy to childhood, and through adulthood. For pregnant women and older adults, changes to the system can be more noticeable at times.

Your health can affect your immune system and vice versa. If you have a health condition, parts of your immune system may not be working well enough, or perhaps too well in some cases. 

All aspects of our lifestyle can have an effect on our immune system, including the amount and type of medications we may take for minor or major health conditions. Different aspects of our lifestyles can also influence the immune system, including diet, stress levels and physical activity levels.

Physical Activity and the Immune System
How does exercise affect your immune system? There is no easy answer, but this is an exciting area of research, with many findings coming to light.

In general, researchers have recently focused on two broad approaches:

i)        What does a single exercise session do to the immune system?
ii)      What does regular exercise do to the immune system?

Exercise is a form of stress on our body. Whether studying the effects of single sessions or regular exercise, researchers generally study the immune system response experienced by people during and/or after exercise.

Single Sessions
We know that even a single session of physical activity has a temporary effect on our immune system. The stress response caused by a single session depends on how fit we are and how hard we exercise during the session.

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Here are some common findings about single session workouts:

  • It has been found that even after a session of moderate intensity exercise (e.g., 30 minutes, involving heavy breathing and light sweating) the immune system can change. More white blood cells will circulate and some will function differently. (For this type of moderate intensity workout, there is no real benefit or detriment to the immune system.)
  • If the exercise intensity is very high and is done for a long period of time (e.g., over an hour), it can be strenuous on the body. Like any stress on the body the immune system will respond. This response can make aspects of the immune system not work as well.
  • Athletes who train very hard may be more likely to be at risk for colds after heavy training sessions or competitions.
  • Research has also found that after an exercise session the immune system returns to normal within one hour, for most people. This return can take longer when the workout has been heavy (long duration and high intensity).
  • It’s during the one-hour window of “immune recovery” when athletes and other who train hard may be more susceptible to colds. The risk may be higher when heavy training sessions are done back-to-back, because the immune system doesn’t get a chance to balance itself out or return to normal between sessions.
  • For a typical workout (e.g., light/moderate intensity, less than an hour), our immune system is not greatly affected.  In fact some researchers argue that a light/moderate workout may actually help to ward of a cold.

Regular Exercise
Research findings about regular exercise are equally interesting. For example, researchers have found that:

  • those who exercise regularly have slight differences in their immune system compared to those who don’t exercise regularly
  • these differences may have many protective benefits for our body and within the immune system itself
  • a major difference is a decrease in prolonged inflammation for those who exercise regularly, for example, in people with heart disease (researchers argue that this decrease in inflammation can help to play a role in the prevention of heart disease and diabetes)

Researchers have also found that for those who exercise regularly, the immune system has a blunted stress response. This indicates the immune system has adapted to regular exercise and can tolerate this kind of stress much better. Just like our muscles adapt to exercise over time, so does our immune system.

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Time to Get Moving
In general, it’s fair to say that research has shown that regular, moderate physical activity can be beneficial to your immune system.

If you are just beginning to exercise more often, here are some tips:

  • Take your time. Your immune system and the rest of your body will need time to adapt to regular exercise.
  • Start at a duration and intensity level you can easily manage. For some that may be 30 minutes, for others, it may be 10 minutes.
  • Keep in mind that positive changes in your immune system are just one small additional benefit you will get from regular exercise. There are many other health benefits as well, such as improved cardiovascular fitness and endurance, and improved flexibility, muscle strength and balance.

For people who exercise regularly, here are a few pointers:

  • Light and moderate exercise won’t be harmful, and in some cases may make you feel better when you are feeling a little under the weather.
  • It’s okay to have a heavy workout, but it’s not necessary to do a heavy workout every day. Your body and immune system need a chance to rest and return to a normal state.

For athletes and those who train hard (at high intensity levels):

  • When you are following a heavy training regime, keep an eye on your health (e.g., watch for signs of feeling worn out or cold/flu symptoms) and try to minimize other risk factors for colds and viruses.
  • Research has shown that consuming carbohydrates before a heavy training session may help to ward off drastic immune changes, making you less susceptible to colds.
  • Other research has shown that vitamin C may also help to ward off drastic immune changes.
  • If you are feeling unwell, it may be best to delay your heavy training session until you are feeling better. 

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Seeking More Knowledge
Given how complex the immune system is, researchers will continue to study exciting and interesting aspects of the immune system, the human body and physical activity.

It’s safe to say that exercise is good for you and your immune system, so take heart… and get moving!

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Learn More

About the Immune System
A helpful article about the basics of the immune system.

Autoimmune Disorders
Basic information from the MedlinePlus online service of the U.S. National Library of Health and National Institutes of Health.

Exercise – Colds and Flu
Basic information from the MedlinePlus online service of the U.S. National Library of Health and National Institutes of Health.

Exercise When You Have a Cold
Information from the WedMD website.

ACSM Current Comment – Exercise and the Common Cold
Information from the American Council of Sports Medicine.

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