The immune system is a fighter. Every single minute it is hard at work locating, hunting, and attacking foreign invaders that come into the body. There are various factors that affect the health of the immune system and can lead to increases or suppressions of certain lymphocytes. Some of these factors include but are not limited to: exercise, nutrition, environment, stress, sleep, drugs, alcohol, and disease. With the focus being placed on exercise here, yes, to a point, exercise is great at increasing the efficiency and healthiness of the immune system4. However, with the increase in popularity of certain marathon sports, intense endurance exercise, and exhaustive training, questions are being raised about how well the immune system is adapting to such an extreme factor. Taking a look at many of the components of the immune system, low and moderate exercise can be contrasted with prolonged intense exercise in the ways that each affects immunity.
VERY BRIEF OVERVIEW OF THE IMMUNE SYSTEM
Each healthy individual is equipped with two branches of the immune system: innate and adaptive. The innate system is present at birth, works very quickly, develops no long-lasting immunity, and consists of the skin, mucous membranes, stomach acid, and phagocytic cells3. Phagocytic cells participate in the direct killing of bacteria by engulfing cells, or in more simple terms, “eating” them. The five phagocytic cells are neutrophils, macrophages and monocytes, basophils, eosinophils, and natural killer cells3. Also included in the innate immune system are dendritic cells that assist with antigen presentation to specialized cells in the adaptive immune system3.
The adaptive immune system is developed throughout a person’s life, working more slowly, but developing memory for the rest of life3. This branch consists of T cells and B cells. T cells are made in the thymus and act in the body to kill cells that have been infected with a virus by activating signal molecules called cytokines3. The two main branches of T cells are CD8+ and CD4+ T cells that are cytotoxic T cells (kill cells) and helper T cells (make cytokines, help B cells), respectively. B cells are made in the bone marrow and work by secreting antibodies, presenting phagocytes with antigens, and secreting cytokines¬3. T cells and B cells mainly reside in secondary lymphoid tissues after they mature until an antigen activates them for further action. These tissues are the lymph nodes, spleen, and skin, and inside of these are mainly where the lymphocytes come into contact with antigens via the blood stream. It is where much of the communication between cells occurs3. Communication begins with white blood cells that have Toll-Like Receptors (TLRs) that fit “lock and key” to molecular patterns on antigens that allow for inducing innate and inflammatory responses including alerting other signaling molecules3. These other signals are cytokines and chemokines which are responsible for inflammation (Tumor necrosis factor-α (TNF-α) and interleukin-1 (IL-1)), recruiting and activation (Interferon-γ (IFN-γ) sent by T cells), differentiation, killing (TNF-α), or proliferation (IL-2, IL-6) of lymphocytes to correspond with what “danger” is being sensed3. Basically, cytokines and chemokines are direction maps that tell the immune cells where the antigen is, what it is, and how to proceed with it.
To make this a tad simpler, picture the secondary lymphoid tissues as a house. Most members of a family (lymphocytes) reside in the house (secondary lymphoid tissues) the majority of the time. Each member of the family has their own rooms (portions of the secondary lymphoid tissue where specialized cells wait), however, sometimes a member gets a bill in the mail (TLR, chemokine, cytokine) and they have to leave the house to pay for it. When members are out of the house, it makes it easy for thieves (antigens) to sneak past and cause damage. Basically, if the lymphocytes are in the secondary lymphoid tissues, it makes it easier to screen the blood that comes through for harmful antigens and is able to keep people from developing illness. This was a very brief introduction to the immune system, but it will help with discussing how each component is affected during exercise.
EFFECTS OF SHORT-TERM AND MODERATE EXERCISE
Exercise is beneficial to the body in the regards of making the heart and muscles stronger, by increasing lung capacity and oxygen movement, and also increases functionality of the immune system. Moderate exercise has been associated with a 29% decrease in developing an upper respiratory tract infection than a sedentary lifestyle77. Acute and moderate duration of exercise has been linked to increases in neutrophil concentrations, CD4+ T cells, CD8+ T cells, and natural killer cells5. This in turn increases phagocytosis within the body of antigens and dying cells to help eliminate any dangers in the blood stream. An increase in CD4+ T cells aids in activation of innate immune cells, B cells, and CD8+ T cells, whereas increases in CD8+ T cells aids in viral elimination. IL-6 is the most prominently locally produced cytokine immediately following exercise that helps initiate recovery of muscle tissue6. Regular exercise has anti-inflammatory properties that help decrease cytokine production and lessen the effect of inflammation on skeletal muscle7. This works by reducing biomarkers for inflammatory cytokines that are on specific muscles so as to not target inflammation to that muscle group. Over time, inflammation of skeletal muscles will lessen as adaptation to exercise occurs. So in regards to short-term and moderate exercise there are positive effects in increases of leukocytes and their activities as well as a decrease in post-workout inflammation.
EFFECTS OF LONG DURATION EXERCISE
Unfortunately, just because a little exercise is good for the immune system does not mean that hours and hours of intense exercise are better. This is not one of those case scenarios where if a little is good than a lot must be great! It is not extra credit, people. Suppression of certain components of the immune system can last from about 3-24 hours post exercise if the exercise is longer than an hour and a half utilizing 55-75% maximum oxygen intake and lacking of food7. This exercise has been linked to suppression of natural killer cells, B cells, and both T cell populations5. Also, secretory IgA, the only antibody that can cross mucus membranes, is inhibited. This leads to a 100-500% increased chance of developing upper respiratory tract infections because the antibody cannot neutralize toxins or keep antigens from entering the blood stream7,4,2,1. For one hour following intense exercise, the lymphocyte subpopulations leave their secondary lymphoid tissues and are circulating in the blood stream, making it more difficult to be presented with antigens5. Taking place in the blood within the innate immune system, are decreases in phagocytic cell activity (mainly macrophages, monocytes, and dendritic cells) and the cytolytic properties of natural killer cells, which decreases all these cells’ ability to uptake, digest, and destroy pathogens4,3. In regards to the cytokines during exercise, IL-6 suppression decreases B cell proliferation and antibody secretion, IL-2 suppression decreases T cell proliferation, IFN-γ inhibition leads to decreases in recruitment of cells, and TNF-α, IL-1, and IL-6 increases lead to inflammation and possible cell death3,4,2,7. Some studies have further shown that increases in IL-6, the cytokine most largely produced during exercise, is linked to muscle damage because of an increase in creatine kinase production that peaks during strenuous exercises and for up to four days after. While IL-6 causes a systemic anti-inflammatory response immediately (which is good), it also peaks IL-1 which is responsible for inflammation post exercise starting after two hours5,6. Clearly, the immune system can take quite a hit when performing intense, prolonged exercises, but not to fear, there are ways to combat the suppression and decrease the chances of developing an upper respiratory infection. Also, remember that every person is going to be different in the ways that their body can handle degrees of intense exercise. Just because studies have found these results does not mean that they are all happening simultaneously or that each person will become immunosuppressed post-exercise.
COMBATTING IMMUNOSUPPRESSION
To sum up, athletes who partake in these long bouts of intense exercise are not deemed “immunodefficient” and they are not in extreme danger of developing major illnesses, however, the risk of common colds and URIs is increased7. Now if intense exercise is the main goal that is being trained for, there are some counteractive protocols that can help decrease the effects of exercise-induced immunosuppression. The easiest way to help the immune system during exercise is to consume carbohydrates both throughout the day and during exercise8. For athletes partaking in endurance exercise, liver and muscle glycogen stores should be fully satisfied by consuming recommended carbohydrates8. However, it is carbohydrates that are consumed during exercise that may have the best effect on reducing any immunosuppression because of the high metabolic rates of immune cells8. Intra-workout carbohydrate consumption helps prevent neutrophil:lymphocyte ratios from rising and lessening their functions as well as continuing T cell proliferation by allowing release of IFN-γ, stabilizing plasma glutamine in order to produce antibodies and maintain/increase natural killer cell cytotoxicity levels, and halting stress hormone cortisol levels from rising which indicates decreased immune function7,8 . Linked to carbohydrate consumption intra-workout, sports drinks and BCAA’s have some substantial aiding effects1,8. The physical act of having liquid in the mouth released IgA, lysozymes, and amylase, if there are carbohydrates present8. These proteins being released all have antimicrobial properties, which help prevent bacteria and viruses from entering the body8. Supplementing with BCAA’s has shown to increase serum glutamine concentrations as well, leading to increased lymphocyte responses, production of cytokines, and lower infection risks1. Aside from carbohydrates, long-term antioxidant supplements such as vitamin C and vitamin E have been shown to slow IL-6 release to allow for longer anti-inflammatory responses 7.
In conclusion, increasing popularity of endurance exercising, marathon sports, and exhaustive training have been linked to increases of upper respiratory infection and immunosuppression in some aspects of the immune system. While moderate exercising is shown to have beneficial effects on leukocyte activity and long term decreases in inflammation, extreme exercise is linked to suppression of cell-mediated immunity, natural immunity, and increases of damaging cytokines. On the upside, vitamins and intra-workout carbohydrates can help slow and prevent some of the harmful effects of intense exercise as well as help to eliminate any bacteria or viruses trying to enter the body. Remember, even if partaking in intense, prolonged exercise, there is no reason to feel in harm’s way of developing a major disease because of a slight suppression of the immune system. The immune system will recover fully and adapt to future training.
By: Rachel Shmagranoff
Disclaimer
All programs and articles provided are intellectual property of James Shmagranoff. No copies or redistribution of these is allowed without express permission from James Shmagranoff. James Shmagranoff is not a doctor and nothing contained within this article is to be taken as medical advice. Always follow the directions of your medical practitioner.
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