It is well documented that moderate exercise prevents many infections and greatly improves immune system function. In contrast, among elite athletes who train at a faster pace and at a higher intensity, the risk of illness increases significantly and the effectiveness of the immune system to fight infections is reduced. Other factors, including exposure to pathogens, lifestyle, sleep and recovery, the overall nutrition of the athlete and the psychosocial aspects should be considered in addition to volume and intensity of training. Each episode of acute prolonged exercise performed at high intensity causes a significant physiological stress on immunity and host-pathogen defense, in addition to having an effect on the level of stress hormones, cytokines, pro- and anti-inflammatories and increased oxidative stress.

From these facts, many researchers have examined the nutritional strategies to implement before, during and after workouts and travel to major competitions to better understand how it is possible to prevent infections in athletes and maintain a strong and healthy immune system. We briefly present solutions for minimizing these concerns as they can greatly affect the performance of your athletes.

Key Points:

• The high intensity training of elite sport significantly increases the risk of illness and reduces the effectiveness of the immune system to fight infection is reduced.
• Nutritional strategies in relation to sleep, stress, recovery, and supplements, implemented before, during and after workouts and travel can help to prevent infections in athletes and maintain a strong and healthy immune system.
• Recommendations include – Isolating athletes who are ill, working with a nutritionist to address the specific needs of the athlete, reducing outside stressors and getting adequate sleep.

1. Food and sleep

The most important aspect in terms of the prevention of diseases and infections among athletes are two main factors that go together: food and sleep. Elite athletes may have an advantage when they pay attention to their diet, ensuring adequate energy intake, intake of carbohydrates and protein to meet their needs and avoiding any restrictions that would lead to a micronutrient deficiency. It is clearly demonstrated that by meeting their nutritional needs, athletes can better maintain their immune function. Athletes must be able to eat three meals a day, including snacks as needed and pay attention to their recovery after each workout to give their body what it needs to be ready for the next workout.

Several studies have shown significant results between the total amount of sleep (number of hours per night) and sleep quality (number of times a person wakes up during the night) as the protective effect of preventing infections in healthy adults. A recent study showed that when 143 healthy adults were exposed to a virus for 14 days, all subjects with poorer sleep quality (who woke up more often during the night) were five times more likely to get sick than those who had a higher quality of sleep. While there is little information on the link between sleep and the rate of infection in athletes, it is still important to put forth this factor to maximize the recovery and performance in athletes and thus reduce their risk of infections.

2. Carbohydrate stress and stress hormones

A nutritional strategy that has shown very successful results through the study is carbohydrate intake during prolonged exercise. From 1995 until the present, a number of studies have shown that ingestion of carbohydrate (~ 60g of carbs per hour) during prolonged exercise (> 2 hours) significantly reduces the increase in neutrophil and monocytes (white blood cells) count, stress hormones such as cortisol and epinephrine, and cytokines such as IL-6, IL-10 recognized for their pro-inflammatory effect. In the negative, carbohydrate intake does not seem to have any effect on immune function or on the oxidative stress caused by prolonged stress. Other studies are looking at nutritional strategies to better maintain these functions and to see if it is possible to add something before exercise or to increase carbohydrates consumed during effort.

3. Recovery after exercise

It is well established that following an endurance exercise > 2 hours, there is a window of opportunity where immune system defence against pathogens is reduced, thereby dramatically increasing the risk of infections. This period may last from 3 to 72 hours after prolonged and intense effort. Studies with marathoners and ultra-endurance athletes have shown that these athletes had more URTI (upper respiratory infections) due to their endurance event than athletes training in shorter distances and for shorter times. It is recommended to eat within 30 minutes of high intensity physical exercise to properly rebuild energy reserves (glycogen) and repair muscle fibers broken during the exercise. This post-workout time allows the athlete to maximize the absorption of nutrients, but also to seize the opportunity of the metabolic and hormonal response to the effort. The body is ready! If the athlete waits too long before eating (1 hour or more) the recovery is compromised and it increases his chances in the long run, to frequently catch infections.

4. Supplements to diminish respiratory tract infections

There is more and more evidence that certain supplements can have a big impact. Supplements such as flavonoids, quercetin and some strains of probiotics (Lactobacillus) may increase some aspects of immune function and thus reduce the incidence of disease in athletes and those who have a weaker immune system . Limited, conflicting or insufficient data, limits interest in supplements such as omega-3, B-glucans, bovine colostrum, ginseng, echinacea or the use of large doses of some vitamins, such as vitamin C and vitamin E. There is also not enough evidence that glutamine and amino acids somehow help to prevent infections. The body has a large storage pool of these nutrients, and studies show that exercise alone cannot significantly reduce these reserves.

A recent hypothesis has been propogated over the latest studies. Because the immune system is so complex and diverse, the approach should rather be to use a combination of supplements rather than studying them individually. It is stated that using large doses of a single supplement may perhaps not be as effective as strategy using a cocktail-type approach with a combination of supplements together.

The table below is a review of all available studies on the use of supplements that can play a role in the immunity of athletes as well as recommendations as to their use.

IMMUNONUTRITION SUPPLEMENT	RATIONALE	RECOMMENDATION BASED CURRENT ON EVIDENCE
Carbohydrate	Maintains blood glucose during exercise, lowers release of stress hormones, counters negative immune changes post-exercise	Recommended: up to 60 g per hour of heavy exertion helps dampen immune inflammatory responses, but not immune dysfunction
Fruit & vegetable extracts rich in polyphenols & flavonoïds	Act as ibuprofen substitutes by attenuating exercise induced inflammation: also decrease oxidative stress.	Recommended: but most research focused on oxidative stress
Quercetin (aglycone and isoquercetin)	In vitro studies show strong anti- inflammatory, anti-oxidative, and anti- pathogenic effects. Animal data indicate increase in mitochondrial biogenesis and endurance performance, reduction in illness	Recommended: especially when mixed with other flavonoids and nutrients.   Human studies show strong reduction in illness rates during heavy training and mild stimulation of mitochondrial biogenesis and endurance performance in untrained subjects; anti-inflammatory and anti-oxidative effects when mixed with green tea extract and fish oil
Bovine colostrums	Mix of immune, growth, and hormonal factors to improve immune function and lower illness risk	Mixed results, and more data needed
Probiotics	Improve intestinal microbial flora, and thereby enhance gut and systematic immune function	Mixed results, and more data needed
β-glucan	Receptors found on intestinal wall immune cells interact with β -glucan improving innate immunity	Mixed results, mushroom β-glucan may be effective, but more data needed
Vitamin E	Quenches exercise-induced reactive oxygen species (ROS) and augments immunity	Not recommended: may be pro-oxidative and pro-inflammatory
Vitamin C	Quenches ROS and augments immunity	Not recommended: not consistently different from placebo
Multiple vitamins and minerals	Work together to quench ROS and reduce inflammation	Not recommended: not different from placebo: balanced diet is sufficient
Glutamine	Important immune cell energy substrate that is lowered with prolonged exercise	Not recommended: body stores exceed exercise-lowering effects
Branched-chain amino acids (BCAAs)	BCAAs (valine, isoleucine, and leucine) are the major nitrogen source for glutamine synthesis in muscle	Not recommended: Not recommended; data inconclusive, and rationale based on glutamine is faulty
N-3 PUFAs (fish oil)	Exerts anti-inflammatory and immune-regulatory effects post-exercise	Not recommended: no different than placebo
Herbal supplements (e.g., Ginseng, Echinacea)	Contain bioactive molecules that augment immunity and counter infection	Not recommended: humans studies do not show consistent support within an athletic content

Source: Walsh et al. 2011

The physiological effects of certain polyphenols such as quercetin, EGCG (green tea extract), turmeric, lycopene and resveratrol generated a lot of interest from exercise immunologists due to their anti-oxidative, anti-inflammatory, anti-pathogenic, cardioprotective, anti-carcinogenic effects. Several recent studies of quercetin supplementation in humans have been conducted to determine its mechanism of action on the post-exercise inflammation, oxidative stress, immune dysfunction, its ability to improve endurance and reduce incidence of infections due to physical stress. When quercetin combined with other polyphenols and nutrients such as green tea extract, iso-quercetin and fish oils, it was noted that there was a significant reduction of inflammation induced by exercise and oxidative stress caused by exertion. In addition, improved innate immune system functions, the ability to defend themselves and to protect themselves from pathogen, are largely increased. Quercetin supplementation (1000 mg / day for 2 to 3 weeks) also reduced the rate of infections in athletes subjected to great physical stress. Quercetin has several bioactive effects and is the polyphenol the most absorbed in the intestine. However, yet to be determined remains the optimal dose for the athletic population and the best cocktail from which they could benefit most during each of the following: periods of intense workouts, trips, and competitions as well as during their recovery.

5. Strategies for travel

As the saying goes: Prevention is better than cure. While there is no exact method to completely eliminate the risk of catching a cold or any infection, there are different lifesytle and nutritional strategies that each athlete can implement on a daily basis, during periods of intense training and when traveling. The following recommendations are made by the group of BASES experts to reduce immunosuppression encountered during prolonged high-intensity efforts and to reduce the risk of infections.

• All athletes, coaches, members of the support team should ensure they have all their shots up to date for travel. The influenza vaccine should be received annually.
• Minimize contact with infected people, young children, animals.
• Keep away from people who cough, sneeze or have a runny nose. When possible and appropriate, ask that these people wear a disposable mask.
• Wash hands frequently: before meals, after touching objects belonging to contagious people, animals, blood, secretions, public places, toilets, public transport, etc..
• Try as best as possible not to put fingers in the face or mouth. Use hand sanitizing gel to wash hands with alcohol (eg Purell)
• Do not share water bottles, cups, napkins, etc.. with your family or among athletes.
• When traveling and on trips, choose cold beverages in sealed bottles, avoid raw vegetables, only eat fruit that you can peel and avoid undercooked meat.
• Quickly isolate other athletes and individuals with symptoms of upper respiratory tract infections (deep cough, runny nose, sneezing, discharge, nasal congestion, etc.).
• Protect the airway from being exposed to very cold or very dry air during strenuous efforts by wearing a mask. The use of a nebulizer after repeated effort in a cold environment is also highly recommended.
• Ensure adequate intake of energy, protein and micronutrients by working with a nutritionist, who will advise athletes on their specific needs.
• Avoid drastic diets and quick weight loss. For sports with weight classes, be sure to follow up with a nutritionist for athletes who find it more difficult to make weight. Make sure that the weight class is well suited to the health of the athlete.
• Make sure there is an adequate carbohydrate intake before and during prolonged intensive efforts to reduce the duration and severity of immunosuppression due to such efforts. Ingestion of 30-60g of carbohydrate per hour during prolonged efforts showed a significant reduction in stress hormones and anti-inflammatory cytokine response during exercise. By minimizing these effects, the risk of infection is reduced.
• The effectiveness of certain “immunostimulant” supplements have not been confirmed (eg Cold Fx, echinacea, etc..) However, there is sufficient evidence in the literature that certain flavonoids (eg, quercetin) and probiotic Lactobacillus strains may reduce the incidence of URTI (upper respiratory infections) in physically active individuals. The daily intake of probiotics may also reduce the risk of gastrointestinal infections. It is recommended that supplementation start at least one week before a scheduled trip, be continued for the duration of the trip and also on return from the trip. Doses of 10 billion bacteria are recommended and should be adjusted according to individual tolerance.
• Wear appropriate clothing depending on the season and the environmental surroundings and outside temperature. Try to keep warm and do not stay in wet clothes after exercise.
• Get enough sleep (at least seven hours per night is recommended). If you are not getting adequate sleep, consider watching and noting the quantity and quality of sleep using non-invasive methods such as motion sensors or some iPhone applications as an interesting way to measure sleep.
• Keep all other stress to a minimum. Consult with a sports psychologist or mental training coach who can greatly help in finding solutions and strategies to reduce this stress and change some behavior or find better coping strategies.