How the Immune System Works: What You Need to Know
The immune system exists to safeguard the integrity of our cells, organs, and systems from pathogens—bacteria, viruses, fungi, and toxins. In short, it works to keep our bodies functioning optimally.

When the immune system is functioning optimally, it can kill off or remove pathogens from the body before you even realize you were exposed, or it uses the minimum amount of time and effort to recover your health after a pathogen has successfully started affecting cell and organ function.

If you have a healthy immune system, it doesn’t mean that you won’t ever get sick. It means that your body will effectively recognize the pathogen and activate the antibodies, molecules that kill or remove pathogens.
If you’ve never been exposed to that pathogen before, then a healthy immune response entails your body building one up in the shortest time possible. While this happens, it usually means you’ll feel ill for a few days.
If parts of your immune system are stressed, damaged, or already addressing another health issue, it may take longer for your immune system to respond and reestablish healthy cells again.
What You Control, What You Don’t, and How That Affects the Immune System
Generally speaking, five factors influence your immune response:

Metabolism: How your body balances energy requirements and distributes energy through the body
Nutritional status: Whether or not all of your nutrient needs are met
Infectious factors: Whether or not you have an infection or are susceptible to infection
Hormonal factors: The concentration of different hormones in the body, including those that strengthen and weaken immune response
Environmental factors: Exposure to toxins, pathogens, and air quality can affect individual immune responses. For example, regarding infectious factors, you may not be able to detect whether there are pathogens present in your environment, but you can wash your hands, clean and disinfect surfaces regularly, and avoid direct contact with people with contagious illnesses.

The effect is similar when it comes to environmental toxins—it is impossible to completely rule out exposure to toxins—they are present in even the cleanest of soil and water systems. However, by understanding where they are in our food and environments, we may choose to avoid certain foods and spending time in certain areas where environmental toxins are present in high concentrations.

When it comes to hormonal factors, you cannot control your genes’ “instructions” on when and how to make hormones, but you can take some actions to modify the hormonal response, including a balanced diet and exercise.

When it comes to your metabolism, like hormones, your genes have instructions on how your body should utilize and process nutrients and their metabolites. However, what you eat and how much you exercise will naturally modify your metabolism so that your body’s needs are met.

And finally, nutrition. There is the misconception that we have complete control over our nutrition—but that is untrue. While the action of eating is normally under our control, what we eat and what we have access to is not. You can read more about the factors out of a person’s control in this article about health behavior science.

Exercise as a Modifiable Lifestyle Factor That Influences Your Immune System Function
Over the past decades, researchers have been debating about the effect of different types and intensities of exercise on immune system response. If you are interested in the research findings, you can read about them here, but in this article we will give you the main takeaways.

This is what we know about how exercise affects immune response:

Exercise has a variable effect on the immune system.

How our immune system responds to exercise depends on:

Intensity
Duration
Exhaustion levels
Mode
Types
To describe how the immune system responds to these different exercise factors, researchers have developed two models: the Open Window theory and the J-Curve model.

The Open Window theory describes how your immune system responds immediately after exercise of different intensities.

Intense exercise results in immediate immune stimulation as you exercise, but your immune system will be temporarily suppressed afterward. If you are exposed to pathogens during that “open window” period, you will be more likely to get ill. With moderate-intensity exercise, you get a slight boost in your immune stimulation during exercise, but it isn’t suppressed.
Principles for Exercising for a Strong Immune System

How can you apply immune system science when building exercise routines for your clients? Here are six research-based principles for building an immune system-strengthening exercise routine:


Practice moderate-intensity exercise, as opposed to light or vigorous exercise. This will lead to an enhanced immune response, a reduced risk of chronic disease, and your body fights the effects of aging on immune function. Moderate exercise equates to 50-70% of your maximum heart rate.
Have a post-exercise snack. Carbohydrate availability helps to reduce the inflammatory response our bodies have after exercise.

Avoid getting exhausted. Exhaustion can compromise your immune system for 24 hours after the event that caused the exhaustion.

Gradually increase intensity and duration of exercise over time. As you become fitter, you’ll need to adjust your exercise so that you remain in the moderate-intensity exercise window.
Make exercise part of your routine: Getting at least 150 minutes of moderate-intensity physical activity a week results in reduced systemic inflammation.

Rest and recover after intense exercise: Vigorous or high-intensity exercise has several benefits for athletes. However, the effect on their immune system is the same. If you do carry out high-intensity exercise, give your body time to rest and recover, and take precautions if you will be exposed to pathogens and toxins.

Main Takeaways
Exercise is one of the modifiable factors that can influence our immune health. While there are several factors that are out of our hands when it comes to immunity, we can apply research principles to promote a healthy immune response if we are exposed to pathogens and toxins that make us sick.