Does Exercise Positively Affect the Immune System?
The immune system is our body’s defence system against external elements such as viruses, bacteria, parasites and fungi. It has been proven that physical activity, following adequate training, activates it, thus strengthening our barriers. Many studies indicate that regular physical activity can significantly enhance the immune system. Research shows that athletes have a higher cytotoxicity, or ability to combat antigens, in Natural Killer cells, which play a crucial role in the natural immune response, compared to inactive individuals. Following a structured exercise programme, including moderate aerobic activity or high intensity interval training, exercise has been shown to increase both the quantity and effectiveness of these vital immune cells, leading to a more robust immune system. Additionally, those who exercise regularly tend to exhibit a stronger adaptive immune response, especially after vaccinations. Research has revealed that elite athletes demonstrate an enhanced response in T cells and antibodies after receiving the flu vaccine. T cells are one of the important types of white blood cells of the immune system and play a central role in the adaptive immune response. Antibodies are a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and latch onto antigens such as viruses and bacteria to remove them from the body.
Can Exercise Have a Negative Impact on the Immune System?
Although the benefits of exercise on the immune system are well established, it is essential to recognize that intense and lengthy workouts can temporarily suppress immune function, potentially increasing infection risk. The high demands of competitive sport, with multiple competitions per week, can cause the immune system to be suppressed. This is what is called immunosuppression. Therefore, a balance between competition and recovery and regeneration is key. All these elements from competition can reverse the protective effect of exercise on the immune system, lowering the defences. This immunosuppression can occur after exercising or it can be due to a lack of sleep, causing the athlete to have alterations in the intestinal microbiota or making him/her have a greater predisposition to suffer infections such as colds or flu. In addition, competition can be stressful. These processes generate cortisol, the stress hormone. If cortisol is permanently high, it can become chronic and be harmful to the immune system. Especially for the Natural Killers, a type of cell in this system, which keep viruses, bacteria and other possible external agents under control.
Research suggests that those engaged in extensive aerobic training, such as cyclists and marathon runners, often show lower white blood cell counts, which are crucial for fighting inflammation, compared to other groups, with 16% of these athletes’ showing counts below the normal range. Furthermore, high-intensity exercise can lead to a short-term decrease in various immune cells, like T lymphocytes, for one to two hours after workouts. This phenomenon, known as the “open window” effect, suggests a brief period of immune suppression that may promote the risk of infections immediately following intense activity. Some studies have found that endurance athletes experience a higher incidence of respiratory infections, such as bronchitis, than the general population, potentially linked to the demands of their training.
The ‘J’ Curve
The relationship between exercise and immune health has been described as a ‘J’ curve, where moderate exercise is beneficial but excessive exertion can hamper immune function. However, this concept is still argued. Recent research indicates that exercise may not always lead to the “open window” effect; instead, the reduction of immune cells in the bloodstream might be due to their movement to peripheral tissues, such as mucous membranes, where they are needed at that time.
Fig. 1. J-curve model of the relationship between the exercise workload continuum and risk for upper respiratory tract infection (URTI). Other factors such as travel, pathogen exposure, sleep disruption, mental stress, and dietary patterns may influence this relationship. This figure was adapted from Nieman. 95. The compelling link between physical activity and the body’s defence system. David C. Nieman a, Laurel M. Wentz b. The_compelling_link_between_physical_activity_and_.pdf
There is ongoing debate about whether athletes are more susceptible to infections compared to the general population. Various factors beyond exercise, such as, nutrition, stress, travel, sleep patterns, and overall lifestyle could contribute to this increased risk. More research is necessary to understand whether intense physical activity compromises the immune system and increases vulnerability to infections.
Summary
In conclusion, consistent exercise offers considerable benefits to our immune system, boosting our capacity to combat infections. Although there remains some debate about whether prolonged intense workouts temporarily weaken our immune defences. It is vital to adjust exercise intensity to support immune health and alleviate stressors that could harm the immune system, including exposure to high volumes of training. Other factors such as significant crowds, elevated stress, insufficient sleep, and inadequate dietary habits should all be considered.