Carbohydrate Intake During Exercise May Prevent Colds
December 01, 2020
Until recently, many scientists believed that exercise reduced the body’s ability to fight infections. Previous studies had found that, for example,
Until recently, many scientists believed that exercise reduced the body’s ability to fight infections. Previous studies had found that, for example, after especially intense exercise, people had fewer white blood cells — which fight infections — in their bloodstream compared to before exercising, suggesting a weakening of the immune response.
But a new review of studies indicates that the interaction between exercise and immunity is much more intricate than previously suspected. Some types of exercise can hinder the immune response, according to the review, while others strengthen it. Encouragingly, it also appears that some simple precautions, including consuming carbohydrates during exhaustive exercise, can help keep our immune system strong.
To learn more about the latest science on exercise and immunity, an interview was conducted with two of the authors of the new review published in the Journal of Applied Physiology. Jonathan M. Peake is a professor of sports science at Queensland University of Technology in Australia, while his co-author Oliver Neubauer is a senior researcher at the same university.
Q. First, why does exercise affect the immune system?
Jonathan Peake: Exercise is a form of stress. The immune system responds to stress.
Q. What actually happens to the immune system during a workout?
Dr. Peake: The number of white blood cells increases during exercise, just as during an infection. Body temperature rises, and immune cells move from lymph nodes, the spleen, blood vessel walls, and bone marrow into the bloodstream. The stimulus here is not overtly infectious, but it occurs due to an increase in stress hormones such as cortisol, epinephrine, norepinephrine, and growth hormone, all of which can increase during exercise.
Dr. Peake: The number of white blood cells in the bloodstream, especially a type of cell particularly good at fighting infections known as natural killer cells (NK cells), drops rapidly. People often have fewer NK cells in their blood after exercise than before they started exercising. For many years, it was thought that exercise was destroying these cells and causing immunosuppression.
Dr. Peake: Now we believe that the cells are not destroyed. Instead, it is more likely that they leave the bloodstream and go to other regions of the body, such as the lungs, intestines, skin, and mucous membranes of the respiratory system. This occurs partly because we can breathe in or ingest microorganisms that end up in these tissues, requiring an immune response, but also because the stress of exercise causes physiological and biochemical changes within these tissues. As a result, signals are emitted from the tissues to the immune system cells in the blood ‘telling them’ that there is a potential threat to the body there, thus causing the immune cells to move there.
Q. So, even though we have more infection-fighting cells in the bloodstream during a workout, many of them end up being diverted afterward to other parts of the body? Can this leave us particularly vulnerable to infections after an intense workout?
Q. What if the exercise is relatively moderate, such as a brisk walk or a gentle run, rather than a more intense workout?
Dr. Peake: Epidemiological evidence suggests that regular moderate exercise protects against upper respiratory diseases, while regular intense exercise increases the risk of these diseases.
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