Exercise Induced Immune Suppression, Why You Should Not Be Concerned
It has been a long standing belief that intense bouts of exercise and heavy training volumes can suppress your immune system making it easier to get sick. Tell me if you heard this before. “I finished [insert intense form of physical activity] and could not train for the next month because I got so sick.” Maybe this has even happened to you. There have even been several studies that seem to back this up, including this one and this one. Some studies have even tried to show the amount of exercise you need to do that puts you at risk. The so called “J curve” of exercise seems to show as exercise volume goes up so does the risk of infection.
This has even been refined a bit into an S shaped curve as it appears that elite athletes can exercise at a high volume but get sick less often.
However, recently there was a review paper published that sheds new light on some of the data from these studies, and it appears that intense and high volume exercise actually does not down regulate the immune system.
The studies above on marathoners based much of their data on the fact that a large percentage of marathon finishers reported upper respiratory tract infections (URTI) after finishing the race. It turns out though that these studies never clinically confirmed that the infections exist, they were just taking the word of the participants. In a study that did actually clinically verify these self reported URTIs only 11 of the 37 reports were actual infections most of which were the result of the common cold. The rest were caused by allergy, asthma, inflammation, or airway trauma.
But 11 still got sick right, so were those caused by the volume and/or exercise intensity? Most likely not. We have to take into consideration what else these athletes are doing. For one, they are racing in a marathon with hundreds if not thousands of other people. We know that the likelihood of getting sick goes up when you are surrounded by large crowds. In addition athletes are notorious for having other confounding factors like much greater stress, nutritional deficiencies, compromised gut health, and cross time zone travel all of which will suppress immune function.
In addition to studies that have looked at URTI in athletes, there have also been studies that look at the changes in lymphocytes (immune cells) in response to exercise. What has been observed is that post exercise lymphocytes drop below pre-exercise levels and then return to normal around the 24 hour mark. This has been referred to as the “open-window hypothesis”, ie a window of time where the athlete is more susceptible to getting sick.
However, recent evidence suggests that in reality there are not less lymphocytes in the blood instead they are being redeployed post-exercise in order to provide an enhanced immune response.
“Here, these immune cells are thought to identify and eradicate other cells infected with pathogens, or those that have become damaged or malignant, termed the acute stress/exercise immune-enhancement hypothesis”
The above findings build a strong case against exercise induced immune suppression. Of course if your immune system is already compromised, or your sleep is off, your gut health is bad, or your diet is poor you might want to consider cutting back on exercise until you can get those things fixed. If however you feel fine and everything is going as planned than there is no reason to think working out will sacrifice your health.