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Athletes with a high training load have a higher risk of catching an upper respiratory tract infection (URTI), such as a cold or flu. The metabolic capacity of immune cells is reduced during recovery, resulting in transient immunosuppression, which usually returns to normal 5 to 6 hours post-exercise. The risk of URTIs is also higher in endurance athletes who report a lack of sleep or significant stress levels.


Here are seven immunonutrition strategies to help you stay in good shape!


1. Adopt a varied and well-balanced diet to prevent excessive energy deficit and nutritional deficiencies.

An inadequate intake of protein, or vitamins and minerals (including iron, vitamin C, and vitamin D) can weaken the immune system. It is best to avoid very restrictive diets and rapid weight loss. Care should be taken to ensure adequate protein and micronutrient intake during periods of voluntary weight loss.


2. Consume a variety of fruits and vegetables.

Many athletes have an insufficient intake of vegetables and fruits. Yet, they are essential foods in order to meet our needs for vitamins, minerals, and fiber. Regular consumption of fruits and vegetables is associated with a lower incidence of colds. It is recommended to consume at least five servings of fruits and vegetables per day, and for athletes ideally even more, since they have a higher energy expenditure. We should also include a variety of fruits and vegetables of different colors each week to meet our nutrient needs. Finally, make sure to include fruits and vegetables rich in vitamin C daily, such as citrus fruits, kiwis, pineapples, strawberries, bell peppers, broccoli, and red cabbage.


3. Stay hydrated at all times and during exercise.

Fluid intake during exercise not only helps to prevent dehydration, which is associated with an increase in the hormonal stress response, but also helps maintain saliva flow during exercise. Saliva contains several proteins with antimicrobial properties, including immunoglobulin A, lysozyme, alpha-amylase, and defensins. Saliva secretion usually decreases during exercise, but regular fluid intake during exercise can limit this decrease.


4. Don't be afraid of carbohydrates.

A low carbohydrate intake before, during, or after intense and/or prolonged exercise can contribute to weakening the immune system. Thus, it is important to consume enough carbohydrates to limit exercise-induced depression of the immune system.


Eating whole, unprocessed foods that are rich in carbohydrates in the appropriate portions for the needs of the organism does not make you "fat," as many people think. Preferred sources of carbohydrates include fruits, vegetables, whole grains, beans, and low-fat dairy products. Athletes who exercise between 1 to 3 hours a day need about 5 to 10 grams of carbohydrates per kilogram of body weight per day, depending on the training cycle, which translates to 340 to 680g per day for a 68kg (150lb) person. To give you an idea of the number of grams of carbohydrates in food, a medium banana contains 30g of carbohydrates, a cup of cooked brown rice contains 45g, and a cup of black beans contains 41g.


Adequate carbohydrate intake should also be consumed before and during exercise to limit the extent and severity of exercise-induced immune depression. Ingesting about 40g of carbohydrates per hour during prolonged exercise (>90 minutes) helps maintain blood sugar, lower circulating stress hormones, and thus help limit the depression of one’s immune function.


5. Avoid excessive alcohol consumption.

Excessive alcohol intake leads to dehydration and impairs post-workout recovery, which can weaken the immune system.


6. Take a vitamin D supplement.

Vitamin D is naturally found in very few foods. The only foods that contain it in its natural form are fatty fish and egg yolks. Other sources of vitamin D in our diet come from fortified foods like milk and some yogurts and plant-based beverages. Exposure to the sun makes it possible to synthesize the majority of vitamin D, but the skin's ability to synthesize vitamin D from the sun decreases with age. An optimal intake of vitamin D can optimize athletic performance through its many benefits on bone health, muscle function, immune function, and inflammatory modulation. More concretely, this means that optimal vitamin D intake could reduce certain factors affecting performance, such as stress fractures, muscle pain, and colds and flu.


7. Other suggested supplements to prevent infections or limit the duration of symptoms:

Lactobacillus and/or Bifidobacterium probiotics (daily doses of more than 1010 live bacteria) may reduce the incidence of respiratory infections in physically active or stressed individuals. A Cochrane review of 12 studies including 3,720 subjects showed a decrease of about 50% in the incidence of URTIs, and a reduced duration of URTIs of about 2 days associated with taking probiotics, but the quality of the evidence was low.


When symptoms of respiratory illness begin, there is evidence that taking zinc lozenges (>75 mg zinc/day; with a high content of ionic zinc) may reduce the number of days that symptoms of the illness will last. Other supplements are promising, such as colostrum and glutamine, but more research is needed.


References

  1. Konig et al. (2000). Upper respiratory tract infection in athletes: Influence of lifestyle, type of sport, training effort, and immunostimulant intake. Exercise Immunology Reviews, 6, 102–120.

  2. Castell et al. (2019). Exercise-induced illness and inflammation: Can immunonutrition and iron help? International journal of sport nutrition and exercise metabolism, 29(2), 181- 188.

  3. Gleeson (2022) What you can eat and do to reduce becoming infected with respiratory pathogens like the corona virus. https://www.mysportscience.com/post/2020/03/12/what-you-can-eat-and-do-to-reduce-becoming-infected-with-respiratory-pathogens-like-the-c

  4. Walsh (2019) Nutrition and Athlete Immune Health: New Perspectives on an Old Paradigm. Sports Med; 49 (suppl 2): 153-168.

  5. Close et al. (2022) Food First but Not Always Food Only": Recommendations for Using Dietary Supplements in Sport. Int J Sport Nutr Exerc Metab;32(5):371-386.

  6. Hao, Dong and Wu (2015). Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev; 3;(2):CD006895.

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