“I’m not feeling well today, I have a bit of a cold. Should I go to training?” Every runner – amateur or professional – must have asked themselves this question at least once during a season. Colds are tricky, and when you consider that endurance sports are a risk group for developing so-called upper respiratory tract infections (URTIs), it’s definitely something to consider before you go out to train. Training and/or competing during a URTI is one of the many issues facing athletes and the doctors that athletes may consult.
Tip: Mild exercise is appropriate if all symptoms are “above the neck”: runny nose, nasal congestion, sneezing, or mild sore throat.
In this LCN Outdoors article, we examine what happens to our immune system during regular physical activity, drawing on the current scientific literature on the subject and backing it all up with some practical advice.
What Happens To Our Immunity When We Exercise?
During exercise, we most often switch from breathing through our nose to breathing through our mouth. We all remember from our childhood biology classes that air through the nose humidifies, warms, and gets rid of large “harmful” particles. This switch from nasal to oral breathing can lead to increased deposition of harmful particles in the respiratory tract. In addition, frequent mouth breathing dries out the respiratory mucosa, disrupting its normal function and slowing down the mechanism for removing dust particles, bacterial debris, etc. The dried mucous membranes become more viscous and simply attract particles.
Immediately after a moderate to high-intensity workout lasting less than an hour, the number and activity of cells in the body that fight viruses increases. However, it has been observed that after high-intensity, prolonged exercise, their numbers may drop below pre-exercise levels in the first two hours after completing such high-intensity exercise.
The same is generally true for all aerobic exercise – the number of immune cells also increases during acute moderate-intensity aerobic exercise, and their function decreases temporarily after the end of intense physical activity. This transient immune suppression – immunosuppression – after acute high-intensity aerobic exercise leads to an immunological “open window” due to which a fully exercised and trained person may be more susceptible to infection after an exercise session.
What Does The Scientific Literature Say?
It should be noted at the outset that there is conflicting evidence in the scientific literature regarding the issue of decreased immunity and disease in endurance athletes. However, there is some evidence that high-intensity training is associated with higher rates of infection. David Neiman of Appalachian State University presented a J-curve, which suggests that regular, moderate-intensity exercise reduces the risk of upper respiratory infections compared to people with inactive sedentary lifestyles. Interestingly, the curve analysis suggests that vigorous exercise increases the risk of decreased immunity and the development of respiratory disease.
Several scientific papers support the Niemann J-curve hypothesis that moderate, regular aerobic exercise reduces the risk of UTIs while performing heavy, high-intensity aerobic exercise increases the risk of immune failure and leads to disease.
Other studies of elite swimmers and distance runners have shown no clinically significant association between exertion, intensity, and concomitant respiratory disease. The exact frequency, duration, type, and intensity of exercise needed to optimally reduce or increase the risk of infection remains uncertain. The incorporation of intensive training into exercise programs during pre-existing infections has been associated with an increased risk of heat exhaustion, post-viral fatigue syndrome, and myocardial inflammation.
Currently, there is no evidence that regular physical activity affects the duration or severity of upper respiratory tract infections in healthy individuals who have exercised.
Speed of Wind
Keep in mind that the feeling of “cold” in a given fall/winter season depends not only on the temperature but also on the wind speed. A moderately comfortable temperature of 41 °F (5°C) will suddenly feel like 32 °F (0°C) with a wind speed of about 13 feet (4 m)/sec, while the perceived “cold” will drop to about 23 °F (-5°C) with a wind speed of about 26 feet (8 m)/sec.
It is important to remember that running itself can increase or decrease this “cold wind” effect. For example, running at 10 miles (16 km/h) in a 13 feet (4 m) second wind “provides” the same cold sensation as standing in a 26 feet (8 m) second gale. For this reason, it’s important to complete all your upwind runs in the first half of your workout on windy fall and winter days.
The second half of the workout – when fatigue slows you down, your body produces less heat and your clothes are damp with sweat – should be run with the wind blowing. Running at 7.5 miles (12 km)/hour with the wind blowing at 10 feet (3 m)/sec completely eliminates the wind chill effect while running at the same speed but against the wind produces a cooling effect like running in a 23 feet (7 m)/sec gale.
Many times the question arises whether exercising in cold weather and inhaling cold air will “freeze” your airways. Generally speaking, if you can inhale most of the incoming air through your nose rather than your mouth, the risk of getting sick is fairly low. Remember, even if the ambient temperature is around 14 °F (-10°C), the air entering your body has heated up to about 59 °F (15°C) by the time it enters your nasal passages. By the time the air reaches your throat, it has heated to about 68 °F (20 °C), and by the time it enters your lungs, the incoming air reaches a temperature of 86 °F (30 °C).
How Respiratory Disease Affects Exercise Performance
Infection is often used as an excuse or an explanation for poor performance. Of course, infections can impair optimal muscle function, and training during illness also requires more effort from the heart and lungs, which in theory and often in practice can lead to poorer performance and worse results. In one study, elite distance and middle-distance runners reported higher subjective assessments of the severity of training intensity during illness, but there was no objective data to support such subjective assessments.
Another study that included elite swimmers did not show any significant decrease in performance during the competition for those athletes who had an upper respiratory infection in the month prior to competition. Another study, also on elite swimmers, reported that although on average the deleterious effects of training during illness were negligible, the chances of harm to the athletes were significant in the long run.
Head And Neck Rule
In general, if you have a cold without a fever, light exercise can be a good solution. Exercise can even help you feel better by “opening” your nasal passages and temporarily relieving nasal congestion.
- Light exercise is appropriate if all the symptoms are “above the neck”. These signs and symptoms include those you might experience with a cold: runny nose, nasal congestion, sneezing, or a mild sore throat.
- Be sure to reduce the intensity and duration of your exercise. Sometimes, it is better to walk instead of jogging.
- Do not exercise if the signs and symptoms are “below the neck” such as general weakness, chest tightness, cough, fever, severe muscle pain, or stomach upset.
Let your body be your coach: If you feel unhappy, take a break. Taking a few days off when you are sick should not affect your performance. Gradually resume your normal training when your condition begins to improve.
If you decide to exercise even during your illness, be sure to reduce the intensity and duration of your workout. If you try to exercise at normal intensity while you are ill, not only is there a high risk but there is also a risk of aggravating your condition, which will cause you to take longer to recover.
Foods To Boost Your Immune System
As you are already aware, intense training puts endurance athletes at risk of developing upper respiratory infections that can keep even the fastest athletes out of action for long periods of time. Prolonged exercise, especially when done without carbohydrate intake and/or adequate energy intake, can compromise your body’s immune system health. In addition, hard workouts can lead to the release of high levels of stress hormones (such as cortisol), which can reduce your body’s ability to fight off infections such as colds and flu. Emotional or psychological stress can add fuel to the fire and worsen your immune system. Add to this a lack of adequate rest and recuperation, especially sleep – a common problem for amateurs. All of these causes will sooner or later lead to a breakdown of adaptation, deterioration of the immune system, and disease.
Oddly enough, nutrition contributes greatly to the health and well-being of the immune system. This critical component is often overlooked when trying to eat and play the “lose weight by any means necessary” game.
There are a number of nutrients that play a key role in maintaining immune function. Inadequate amounts of vitamins A, C, E, B6, B12, and folic acid in the diet can lead to impaired immunity, resulting in decreased resistance to infection. It is now well established that vitamin D plays an important role in immunity and it has been shown that deficiencies of this vitamin are common in athletes, especially in situations where natural sunlight exposure is limited, as it is in many areas during the fall and winter months. In a study published in 2013, the authors measured the vitamin D levels of 225 endurance athletes at the beginning and end of a 16-week winter training period. The results showed that athletes who were deficient in vitamin D were more likely to suffer from upper respiratory illnesses, such as colds, than those with normal vitamin D levels.
Some minerals also affect immune function, particularly zinc, iron, and magnesium, which can be depleted by regular heavy exercise. omega-3 fatty acids and flavonoids (a nutrient found in many plants) have also been shown to play an important role in maintaining a healthy immune system by reducing oxidative stress and inflammation.
There is now a great deal of research interest in the role of gut bacteria (known as the microbiome) in immunity. For example, the beneficial bacteria contained in probiotics help to inhibit the growth of harmful bacteria. Probiotics can also influence immune function by interacting with immune cells in the gut, and as a review of 12 studies showed, regular intake of probiotic supplements can reduce the incidence of respiratory infections by 50% and reduce symptoms by 2 days.
Practical Tips: Eat, Wear, Exercise
To support your immune system, it’s a good idea to eat the foods from the list below regularly, paying special attention to post-exercise recovery meals, which should include fruits/vegetables as well as carbohydrates and protein. Try to eat a varied diet rather than eating the same thing, even if it is on a regular basis.
- Vitamin C: peppers, oranges, kiwis, berries, potatoes.
- Vitamin E: avocado, almonds, seeds, oats, brown rice.
- Vitamin A: orange and dark green vegetables and fruits, such as hazelnut pumpkin, sweet potatoes, mangoes, apricots, broccoli, spinach.
- Folic acid: green leafy vegetables, such as broccoli, spinach, cauliflower, cabbage.
- B vitamins: lean meats, dairy products, whole grains. Note that vitamin B12 is only found in animal products, so vegetarians may need to take supplements or eat foods fortified with vitamin B12.
- Vitamin D: eggs, oily fish, such as salmon and mackerel. Please note that vitamin D is only present in very small amounts in food and is useful to take supplements in the winter when the sun is not strong enough for the body to produce vitamin D on its own.
- Zinc: eggs, turkey, almonds, cashews, oysters.
- Magnesium: whole grains, nuts, seeds, green leafy vegetables.
- Iron: lean red meat, lentils, chickpeas, cashews, apricots, whole wheat bread.
- Omega-3 fatty acids: salmon, mackerel, anchovies, trout, sardines, fresh tuna, ground flaxseed, chia seeds, flaxseed oil, walnuts, pumpkin seeds.
- Flavonoids: green tea, berries, apples, onions, black tea.
- Probiotics: fermented foods such as live yogurt, kefir, tea tree mushrooms, sauerkraut, sourdough bread, miso soup. It is also important to eat a variety of plant-based foods to obtain prebiotic fiber, which stimulates the growth of probiotics in the intestinal tract.
In addition to diet, the following strategies should be considered.
- Consume 30-60 grams of carbohydrates per hour in the form of an energy drink or gel during workouts that last more than an hour. Carbohydrate intake has been shown to reduce the release of immune-suppressing cortisol and cytokines during exercise.
- If you are prone to colds and infections, or are recovering from an illness, avoid exercising on an empty stomach as this can put additional stress on your body. Eat a banana or drink 250 ml of diluted juice in the morning before your workout. The potential benefits of fasting may be outweighed by the days lost to illness after training. If you choose to fast or train low-carb to improve training adaptations, do so no more than twice a week, and avoid high-intensity training during such sessions. Also, make sure to include at least 60 grams of carbohydrates in your post-workout meal and your next meal.
- Don’t reduce your fluid intake. It’s true that you sweat less in cold weather compared to hot weather, but an intense exercise in cold weather can still lead to dehydration.
- Take in enough carbohydrates with your food. Cold weather increases the rate at which muscles consume carbohydrate stores, so depleting glycogen stores can be a problem.
- You don’t want to overeat. There is nothing to be gained by increasing the subcutaneous fat layer. It’s true that fat people feel more comfortable than thin people when both are standing in the cold air, but things change during exercise. Physically active and healthy people can usually exercise more intensely than normal healthy people, and therefore can produce more internal heat. An exception to this rule is swimming, where a little fat under the skin prevents heat from escaping too quickly into the water.
- If you run regularly, use at least two different pairs of running shoes. This recommendation is due to the fact that harsh weather conditions often make running shoes soaking wet. The midsole is particularly affected, and once wet, it cannot absorb impact loads as well as a dry midsole. Therefore, it is best to leave the soaked shoes until they are completely dry before using a second pair for the next workout.
- In very cold weather, find a place to train that is at least partially sheltered from the wind. This will allow you to train more effectively and reduce the risk of catching an excessive cold.
Take care of yourself and make exercise good for your health.