Nutrition and Immune Function in Athletes

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NUTRITION AND IMMUNE SYSTEM IN THE ATHLETE How can it help you?

Each of us, according to different studies, presents various upper respiratory symptoms such as the cold between 2-4 times a year. Some athletes refer to the cold as the "most feared opponent of the Olympic Games". A few years ago, the New York Times reported the story of Finland's Olympic skier Lare Lethones. Lethones suffered from an atrocious fear that his children would become small vectors that would transmit a virus to him and thus ruin his participation in the Olympic Games. Such was his concern that he took them out of school and did not allow them to go to birthdays or places where there were crowds of people. He didn't do it to be an overprotective father but to prevent a cold from ruining his participation in the Olympic Games. Whether or not their behaviour was exaggerated, the data show that the common cold is not exceptional in athletes, being one of the greatest causes of loss of training and competition time in elite sport.

In 2018, the prestigious British Journal of Sports Medicine published a prospective article on the common cold in the Finnish team during the 2018 Olympic Games. Of the 44 athletes, 20 of them experienced cold symptoms and of the 68 of the accompanying technical team, 22 were also affected in the 21 average days of stay. The culprits are seven different viruses, such as different strains of coronavirus, influenza B, respiratory syncytial virus, rhinovirus and human metapneumovirus. The Summer Olympics are not spared either, for example in those held in Brazil during the summer in 2016 one of the main causes of disease were those related to the upper respiratory tract.

These data have put exercise as the main culprit in the drop of the athlete's immune system for more than a hundred years and related to an "increased risk" of upper respiratory diseases. From the '80s, several studies were published showing that after prolonged endurance events such as the Marathon of the Two Oceans in 1983 or the Los Angeles Marathon in 1987, there was a higher incidence of upper respiratory symptoms in the weeks after the events. The famous "Open Window Theory" was formulated in which it was explained that exercise produced a transient drop in immunity after exercise and, therefore, during this period the athlete was more likely to get sick. Professor Nieman in the '90s proposed the relationship between exercise and susceptibility to infection in the so-called "J" model of immunity. According to Nieman, sedentary people have a medium risk of infection while athletes have a higher risk of opportunistic infections, especially of the upper respiratory tract. However, people who exercise moderately are at lower risk. Not all scientists agree with this theory that athletes experience more risk of infection than the general population. The Open Window Theory began to be challenged in the year 2000 with the results of a study carried out on athletes who ran the Stockholm Marathon, where it was observed that the symptoms were not greater after the race in those who had not shown symptoms prior to their participation in the event. Recently, this theory has been debated with some arguments that seem quite reasonable.

As you can understand, it is not very compatible to be an elite athlete, win medals and have a high frequency of disease. In fact, several studies show that medal winners in the Olympic Games or world championships experience fewer or shorter respiratory tract infections than athletes at the national level. Therefore, he thinks that "the less sick an athlete gets, the more they can train". These data have led many scientists to propose changing the "J" model proposed by Professor Nieman to the "S" model. It would make sense to think that athletes may have evolution in their favor, also in certain aspects that have to do with their immunity as shown by some studies where it is observed that there are certain polymorphisms that determine a more effective immune response in some athletes. Therefore, it would seem obvious that elite athletes also have a more "robust" immune system capable of fighting infections during and after repetitive and intense exercise, in a way that allows them to achieve success.

Medal winners—the best athletes—do not seem to suffer as many infections as other athletes. Genetics together with other factors such as greater education and hygiene can favor a lower frequency of disease.

Other factors are also discussed and quarantine the old axiom that exercise increases the risk of infection in athletes. However, today the athlete faces different factors that can contribute to the fact that there is a greater risk of infection, such as psychological stress, lack of sleep, environmental stress, travel, inadequate nutrition or a period of high training load.

How can nutrition help you? An individual's nutritional status influences both susceptibility to infection and their response in terms of clinical outcomes. In the case of athletes, strategies are currently used where training is done with low availability of both exogenous (external contribution) and endogenous (reduced glycogen levels) carbohydrates. These strategies are deliberately implemented and used at certain points in the athlete's training planning in order to amplify the adaptations that derive from the training itself. Studies so far do not show that these types of strategies performed acutely significantly disrupt athlete immunity, leading to an increased risk of respiratory tract infections.

One of the nutrients that has been most closely linked to immunity is carbohydrates. Although it is obvious that they have a fundamental role in performance, in vivo studies have not shown clinically relevant results in the incidence of upper respiratory symptoms.

The availability of nutrients can affect immunity due to its role in different immune processes.

As for the recommendations for protein intake in endurance athletes, these are around 1,6g/kg body weight and day. However, higher doses may be interesting to support immune function at certain times of the season when training or competition loads are high. For example, a study carried out on cyclists showed how the intake of 3g/kg/day versus 1,5g/kg/day of protein helped to reduce the drop in different immunological parameters during periods of high intensity.

Hydration plays a very important role in mucosal immunity, so dehydration can have effects on our defenses. During exercise, sympathetic activation can reduce the flow of saliva in our mouth. Saliva contains antimicrobial proteins such as alpha amylase, lysozyme or immunoglobulin A. Some studies have shown that dehydration affects the concentration of some of these proteins, which could make us more vulnerable to upper respiratory infections.

Most of the studies that have shown some benefit in supplementation come from people with compromised immunity or laboratory trials, however, there are a limited number of nutritional strategies and supplements whose efficacy is supported by different scientific studies.

As for supplements, most of the data supporting their use on immunity comes from studies conducted on people with compromised immunity. This would make us think that a supplement can do little for you if you have adequate levels of the nutrients it provides. However, there are several real-world scenarios in the athlete and data that indicate that some of them may play a relevant role. For example, in situations where energy, macro and micronutrient intake may be insufficient, such as in the case of weight loss diets, or at times during which there may be a decrease in immunity and/or increased exposure to pathogens, such as in foreign travel, competitions or training during the winter.

In a review by the Conchrane group on vitamin C and cold, it is reported that 200mg or more a day of vitamin C has no effect on reducing the number of colds. However, a moderate reduction in symptoms is observed and, interestingly, in those who go through periods of extreme physical stress such as runners or skiers, reducing the risk of colds by half.

Vitamin D is acquiring an increasingly important role in the health of the athlete. The relationship between this vitamin and immunity is not new. Vitamin D has different functions that go beyond calcium homeostasis. Today its role in musculoskeletal function and also in immune function is recognized. About 80-90% of this hormone is produced in the skin when ultraviolet B radiation reaches the epidermis. Through a series of steps, culminating in the kidney, 1,25-hydroxyvitamin D3, the active form of vitamin D, is formed. We can also obtain this vitamin through the diet, however, its contribution is small. The discovery of vitamin D's role in immunity seems quite relevant. It has been seen, for example, that this vitamin increases the expression of genes that give rise to antimicrobial proteins such as cathelicidin or defensins. In a study conducted by He et al., it was observed that those athletes who had inadequate or deficient levels of vitamin D had a longer-lasting cold and poorer mucosal immunity. In addition, those athletes with optimal vitamin D levels had a higher production of immunoglobulin A. These data, along with others that reinforce vitamin D's role in immunity, should be considered. In this sense, there are several studies that indicate that in a large number of athletes from different countries and sports, especially in autumn and winter, the levels of this vitamin are not adequate. The evidence seems clear, deficiencies of this vitamin should be avoided to maintain immunity and prevent respiratory infections in athletes. During the winter months, a supplement of 1.000 IU may be sufficient. Different foods can help, such as eggs, dairy, salmon, and mushrooms. Don't forget that supplementation should be prescribed by a health professional, don't "self-supplement" without knowing if you really need it and how much you need.

Zinc is a very important micronutrient in immunity, participating as a cofactor in hundreds of enzymes and intervening in the development of the immune system and its function. Some athletes may put zinc intake at risk if their diet is not well adjusted. This can be the case for vegetarian athletes. Since the main sources of zinc are found in foods of animal origin, such as meat, fish and seafood, it is necessary for these athletes to ensure that they ingest rich sources of this micronutrient such as wheat germ, asparagus, spinach, nuts and legumes, although in some cases, the fiber content can decrease its absorption. Zinc deficiency in athletes is not uncommon, especially in those who follow weight loss diets or in endurance athletes, who can eliminate this mineral through sweat and urine, the latter route increased with exercise. As for zinc as a supplement for prevention, I do not recommend that this be part of your day to day, there are different side effects that can harm your health. This happens with many micronutrients, since their supplementation without a prior assessment of their status can trigger interactions with other micronutrients producing their deficit, for example, an excess of zinc can lead to a deficiency in copper, a mineral that is also important for the immune system. In the event that cold symptoms occur as soon as possible, if possible within 24 hours of onset, zinc acetate supplementation (75mg/day) can decrease symptoms by up to 40% and shorten the time of illness by about three days, at least this is indicated by a recent meta-analysis of the literature. Here you should look for the amount of elemental zinc contained in the supplement. You need between 10-20mg and let it dissolve in your mouth. Remember to avoid taking for longer, side effects may appear.

The deficiency of a nutrient required for the proper functioning of the immune system decreases its capacity and increases the susceptibility to infection..., therefore, the first thing you should ensure is that your diet contains adequate sources of these nutrients.

The last measure I bring you tries to support the largest mass of lymphoid tissue in the body where there are thousands of different microorganisms. Today we know that our microbiota can be modified by diet and other external factors. For example, the consumption of probiotics can modify it in a positive way. Probiotics are living organisms that, when administered regularly and in adequate amounts, confer a health benefit to the host by modulating the bacteria that live in the gut (the so-called microbiota).

A Cochrane systematic review concluded that probiotics produced a decrease of almost 50% in the incidence of upper respiratory infections in the general population and shortened the duration of symptoms by about two days. However, the quality and number of included studies as well as possible brains should be considered. In an interesting study by Cox et al., the beneficial effect of a dose of 1,3 x 1010 million colony-forming units of lactobacillus fermentum was shown during 28 days in runners during the winter period. The number of days and symptoms were 50% lower in those who received the probiotic compared to those who did not. In addition, there were also changes in some immune factors such as interferon gamma, although not others. Make sure you take a supplement that contains a minimum of 10 trillion bacteria. If you need to take, look for reliable brands that properly and truthfully display the content. More studies are needed on the effects of probiotics in athletes, but for now, supplementation could be considered, particularly in periods where there is an increased risk of respiratory tract infections, such as in the weeks leading up to and during travel abroad.

FINAL RECOMMENDATIONS

• Avoid your enemy. Proper hygiene is essential.
• Control the training load and recovery.
• Sleep is the cornerstone of your immunity.
• Stress is neither too much nor too little. Meditation can be a good tool that can help you.
• A proper diet will not save you from catching a virus but it will, in some cases, reduce your ability to "fight" against it. Avoid nutritional deficiencies by having the premise "food first".
• Avoid very aggressive diets.
• Adapt your carbohydrate intake to the needs of the day and don't forget to have an adequate protein intake.
• Assess your vitamin D from autumn to early spring and consider supplementation if necessary.
• At the beginning of the cold, zinc acetate (75mg/day) can help decrease symptoms and shorten the time of illness.
• Consider probiotics in certain circumstances (≥1010 live bacteria/day) before or during trips abroad.

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AUTHOR

Fernando Mata Ordoñez Managing Director NutriScience Spain – www.nutriscience.es