Moderate exercise is healthy for your immune system, just as it is for other organs and tissues in your body. Regular physical activity also enhances the immune system’s ability to fight off infection and that’s what you need to avoid seasonal bouts with viruses. In fact, some studies show that regular physical activity daily reduces the risk of catching a cold by 50%. So, consistent exercise has benefits for immune health.
As they say, everything in moderation. More of something isn’t always better for your health, except for maybe broccoli. Intense workouts or workouts of long duration can make you more susceptible to catching a cold or upper respiratory virus several hours afterward. During this “window period,” your odds of being sidelined with a cold are higher if you’re exposed. What is it about exercise that causes a short-lived boost in the odds of catching a cold? Here’s what scientists believe are the reasons.
A Rise in Stress Hormones
Intense exercise places stress on your body. You can feel it during and after a workout, as your muscles burn, the sweat flows, and fatigue sets in. In response to that stress, the stress hormone cortisol rises. During times of stress, your adrenal glands, located just above your kidneys, pump out more cortisol to supply your body with the fuel it needs, in the form of glucose, to “fight or flee” the source of stress. Cortisol serves a useful purpose, but it also suppresses your immune system’s ability to fight off viruses and other pathogens. The rise in cortisol is greatest after periods of intense exercise or exercise of long duration.
Transient Increase in Inflammation
The stress of intense exercise can also cause a transient increase in inflammation. This has been confirmed by blood tests showing that markers of inflammation increase after a workout. This isn’t a bad thing long term since the inflammation is short-lived, and over the long term, research shows that regular physical activity helps reign in low-grade inflammation. In fact, a meta-analysis of 11 studies involving 1,135 healthy adults found regular physical activity reduces markers of inflammation including IL-6, C-reactive protein, and TNF-alpha. That’s a benefit for your health.
Reduced Antibodies in Saliva
You might not know it, but you have antibodies in your saliva that protect against viruses. These antibodies are known as immunoglobin A (IgA) These are the same protective antibodies in tears and the mucous that lines the intestinal tract. Studies in people who do long-distance endurance exercise, like running marathons, show that IgA in the saliva drops after intense exercise or long periods of endurance exercise. Such a drop makes it easier for respiratory viruses to gain a foothold.
Reduced Activity of Natural Killer Cells
Natural killer cells are a type of cell that kills viruses and tumor cells upon contact. Studies show that natural killer cell activity drops by 50% for 5 to 6 hours after an intense workout. But how natural killer cells respond to a workout depends on its intensity and duration. Moderate exercise increases natural killer cell activity, providing a protective effect, while excessive training and nutrient deficiency can have the opposite effect on natural killer cell and immune system activity. So, don’t overdo it and give your body enough rest and recovery time after a tough workout.
A Decline in Nasal White Blood Cells
Your nasal passages also have specific types of cells called neutrophils that fight bacteria and viruses that enter your nose. Studies show that the levels of these cells drop after an intense workout. With this drop, you may become more susceptible to viral infection due to reduced immune surveillance.
How to Lower Your Risk
Now you know why you’re at higher risk of catching a cold after an intense workout, but what can you do to lower your risk of catching an upper respiratory infection? One strategy is to consume a post-workout snack that includes carbohydrates. Most sports dietitians recommend a snack with a ratio of three parts carbohydrate to one part protein. Why does this work? Carbohydrates raise blood sugar and that suppresses the release of cortisol and that helps keep your immune system primed.
Don’t overtrain either. It’s okay to do high-intensity workouts, but give yourself at least 2 days of rest between intense training sessions. The rest will help your body recover as well as your immune system. Ensure that you’re getting at least 7 hours of sleep per night too. Lack of sleep is another lifestyle factor that can affect your immune system. Finally, make sure you’re eating a nutrient-dense diet and getting enough of the key nutrients that support immune system health, including vitamin A, vitamin C, vitamin D, iron, selenium, and zinc.
Take steps to manage stress too, as physical and mental stress can suppress your immune system. Meditation, yoga, and controlled breathing are strategies that calm and help with stress control. Stress can also cause a sharp rise in cortisol that makes it harder to fight off infection. Plus, it’s not good for your metabolic health.
Make sure the humidity in your home isn’t too low. Low humidity, more common in the winter, causes your nasal passages to dry out, allowing viral invaders to more easily gain food hold. The ideal humidity for your home and sleeping area for cold prevention is around 50%. If you get frequent colds and upper respiratory infections, invest in a humidifier to add moisture to the air.
The Bottom Line
High-intensity workouts burn mega-calories and boost cardiovascular health too, but there’s a window period of a few hours after such a workout that you’re at higher risk of catching a cold or upper respiratory virus. Be sure to eat a post-workout snack that includes carbohydrates and do the other basics like letting your body rest for a few days after a hard exercise session and getting enough sleep. Make sure your diet includes enough calories and is nutrient-dense. Skip the sugar, as it’s empty calories, and there’s some evidence that sugar suppresses immune function too.
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- Biol Sport. 2012 Dec; 29(4): 255–261.Published online 2012 Nov 15. doi: 10.5604/20831862.1019662.
- European Journal of Applied Physiology and Occupational Physiology volume 67, pages180–184(1993)
- British Society for Immunology. “Immunity in the salivary gland”
- Sports Med. 1994 Nov;18(5):340-69. doi: 10.2165/00007256-199418050-00006.
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