Topic 8. Immunity
p. 313-321
Texte intégral
Questions and answers
Key points
■ Although moderate sport reinforces the body’s immune system, intense sport increases the risk of infections, especially during competition periods.
■ Some minerals (copper, iron, selenium and zinc) and several vitamins (A, B6, B9, B12, C, D and E) are necessary for the immune system to function properly. They should primarily be obtained through food.
■ Some food elements appear to help limit the negative consequences of intense exercise on the immune system. These are probiotics and polyphenols, especially quercetin.
Does sport make you more resistant to or, on the contrary, more sensitive to infections?
1Exercise appears to have a protective effect on the body’s immune system. For instance, if we compare people who take part in sport and those who do not, the number of days of infections registered during the three months of winter are almost two-fold lower (-46%) in the athletes. However, the relationship between sport and risk of infection is not linear. Thus, “the more I train, the better protected I am” does not apply! On the contrary, while moderate training has a beneficial effect in terms of prevention, very intense sport greatly increases the risk of infection.
2Among infections, the type most commonly reported in athletes are respiratory infections (rhinitis, rhinopharyngitis, angina, bronchitis).
Is the risk of falling ill seasonal?
3Unlike in the general population, symptoms of infection do not appear in athletes on a seasonal basis, rather they are closely linked to competition schedules.
4Thus, the phase of intense training preceding a competition is one of the periods during which the risk of infection is increased, because in addition to the negative effect of intense exercise, other factors such as stress or lack of sleep also damage the immune system. In addition, if competitions take place abroad, exposure to unfamiliar environmental microorganisms enhances the risk.
5The days, or even weeks, following a competition are also a risk period, especially in endurance sports. Thus, during the two weeks following an intense endurance event, participants are twice as likely to get sick as people who have not taken part in this type of event. This phenomenon is part of the “open window” theory, according to which strenuous exercise leads to a weakening of the immune system for between 3 and 72 hours. During this period when the immune system is weakened, the athlete runs a higher risk of developing an infection.
Can diet weaken the immune system?
6A significant reduction in energy intake is associated with various upheavals in the immune system. For instance, it was shown that losing 2 kg body weight over two weeks affected some immune parameters. By the same token, the immune system is weakened in judokas combining physical exercise and calorie restrictions.
What minerals and vitamins are necessary for the immune system to function properly?
7The immune system is complex, and, to function optimally, requires a well-defined nutritional environment. In this respect, some micronutrients are necessary. These include vitamin A, some B vitamins (B6, B9, B12), vitamins C, D and E, as well as zinc, iron, copper and selenium. To maintain the immune system, the first step is to ensure appropriate levels of intake of these different micronutrients (see Fact sheet No. 11 Balanced diet, p. 358).
Can vitamin/mineral supplementation reduce the risks of infections?
8The most studied vitamin in this context is vitamin C. Increasing intake of vitamin C does not decrease the immune upheavals caused by physical exercise. The results of a meta-analysis show that vitamin C consumption does not have any preventive effect on respiratory infections except in the case of athletes performing intense exercise, especially when they are exposed to cold temperatures. However, when taken after the symptoms appear, vitamin C has no impact on the severity or duration of the infection.
9During the two months of winter, consuming cereals enriched in different minerals and vitamins thought to boost the immune system did not provide conclusive results, either for the immune system or for respiratory infections.
10In general, it is recommended that vitamin and mineral supplements be taken with care: indeed, it is not because a vitamin is necessary for the immune system to function correctly that increasing intake proportionally reinforces the immune system. On the contrary, some micronutrients can cause problems when taken in large amounts. This is the case with vitamin E, where supplementation in athletes caused the opposite of the expected effect. Therefore, although vitamin/mineral supplementation (corresponding to food intake) can be useful, megadoses (several dozen times greater than the Dietary Reference Intake) are really not recommended.
What exactly are probiotics and how are they useful?
11Probiotics are living microorganisms (mostly bacteria and yeasts) which, when consumed in sufficient quantities, have beneficial effects on health. They are mostly found in yoghurt or fermented milks, but they are also available as supplements.
12Probiotics have been shown to have two different effects in athletes: they limit respiratory infections and can help prevent intestinal disorders, especially “traveller’s diarrhoea”.
13For respiratory infections, interesting results were reported in athletes, with a 40 to 50% reduction in the number of infectious episodes or in the number of days of sickness in people consuming probiotics during the four months of winter compared to people who did not. However, this beneficial result is not systematic, and may be more relevant to athletes who are subject to recurrent infectious episodes. This is because probiotics appear to have a greater effect in people with an inefficient immune system. There is also a gender bias, with increased effects in male athletes.
14The other advantage of probiotics is their capacity to limit intestinal disorders. These microorganisms prevent diarrhoea, which is particularly useful for those having to adapt to unfamiliar environments, such as when athletes take part in international competitions. Probiotics also limit stress-related gastrointestinal disorders (abdominal pains and nausea/vomiting). Thus, they are potentially of great interest for stress-sensitive athletes, those subject to intestinal problems, or those taking part in competitions abroad. Nevertheless, probiotics should not be taken just before an event unless they have been tested beforehand, because they may initially cause slight intestinal discomfort, which normally disappears after seven to ten days. This may seem paradoxical, but it simply reflects the need for the digestive system to adapt to new bacteria.
15Although probiotics have numerous interesting properties for athletes, it is difficult to generalize their effect on the immune system because this differs from one bacteria to another. The effects of bacteria also depend on the immune status of the person ingesting it; there can thus be considerable inter-individual variations. This makes it difficult to give general recommendations. Supplementation with probiotics could be useful for athletes subject to recurrent respiratory infections or intestinal disorders, but medical advice should be taken before starting this supplementation. In addition, it is important to remember that no product, whatever its nature, should ever be used for the first time during a competition.
Can consuming energy drinks during exercise prevent infections?
16Consuming energy drinks during exercise is only partially effective in preventing infection. Even if they reduce some of the deleterious effects of exercise, particularly some inflammatory parameters, they have no impact on immune system parameters: therefore, they do not decrease the incidence of infections during high-risk periods.
What other nutritional factors can help prevent infections?
17An important number of food substances have been tested to see if they can eliminate the negative consequences of intense physical exercise on the immune system. The oldest studies analysed the effects of amino acids such as glutamine and branched-chain amino acids. Given the poor results obtained, research turned to other nutritional components like colostrum, omega-3 fatty acids (fish oil), β-glucans, some plants (echinacea, ginseng) and polyphenols (vegetable-derived substances which have beneficial properties for the body) such as quercetin, curcumin, and resveratrol.
18So far, the most promising results have been obtained with β-glucans, colostrum and some polyphenols, particularly quercetin. But the recent enthusiasm for these substances does not allow the necessary detachment to give precise recommendations.
19The hypothesis currently emerging is that the immune system is highly complex, and that a mixture of various potentially beneficial elements is probably more efficient than any single substance, even if taken in large amounts.
Practical applications
1. A solid base
Foods which are important for the immune system

2. Avoid weakening your immune system
20► During high-risk periods (training courses/intense training, competitions, winter):
21› Avoid restrictive diets
22› Have a sports drink during training (See Fact sheet N° 10 Hydration, p. 342)
3. Take care of your gut flora
23Probiotics are “friendly” bacteria. Eating them helps strengthen the immune system.
24► Where are probiotics found?

4. Stock up on polyphenols
The advantages of polyphenols
25► Polyphenols are contained in some vegetables
26› They can help athletes because they play a role in boosting the immune system and preventing infections
Sources of polyphenols

In particular
Red berries: blackcurrants, blueberries, raspberries, stawberries, red grapes
Vegetables: broccoli, cauliflower, spinach

In particular
Green tea, (grape, pomegranate, citrus fruit, cranberry1) juice, alcohol-free beer

In particular
Dark chocolate, sugar-free cocoa
Recipe
Guinea-fowl supreme with mixed nuts and seasonal vegetables

Photo credit: Thibaut Ruggeri.

27Serves 2
28Preparation time: 45 minutes
29Cooking time: 30 minutes
30Difficulty:
31Guinea-fowl
32■ 2 guinea-fowl supremes*
33■ Salt and pepper
34■ 15 g dried apricots
35■ 10 g dried figs
36■ 10 g pitted dates
37* Supremes: poultry breast with skin
38Open the guinea-fowl supremes in two, from the side of the meat, and season. Chop the dried fruit and stuff each supreme before closing it again.
39Roast the almonds and hazelnuts in the oven at 180 °C.
40Crush the nuts.
41Brown the supremes on both sides with the shallots and olive oil.
42Add the veal stock and season.
43Mixed nuts
44■ 10 g almonds
45■ 10 g hazelnuts
46■ 10 g pistachio nuts
47■ 40 g shallots
48■ 10 g olive oil
49■ 60 g veal stock
50■ Salt and pepper
51Vegetables
52■ 100 g baby potatoes
53■ 100 g carotts
54■ 100 g broccoli florets
55■ 200 g cleaned spinach
56■ 1 garlic clove
57■ 10 g olive oil
58■ Salt and pepper
59Sprinkle the crushed nuts onto the skin of the meat and roast in the oven at 180 °C for 20 minutes.
60Peel and chop the carrots, then cook them, covered, in a saucepan of boiling, salted water.
61Wash the potatoes and boil them.
62Cook the broccoli in salted water.
63Wilt the spinach in a pan with a small amount of oil and the garlic for 5 minutes. Season and drain.
64Place the spinach in a mound in the centre of the plate, cut the guinea-fowl supreme in two and place it on top of the spinach. Arrange the vegetables around the mound. Add the gravy.
65Serve in a deep plate.
66Chef’s note
67This dish is particularly rich in micronutrients that boost the immune system. It easily covers the Dietary Reference Intake (DRI) for vitamin B9 and β-carotene, and provides half of the DRI for vitamin C, vitamin E and zinc. It is also a good source of copper and iron.
68Nutritional analysis per person
Energy (Cal) | Carbs (g) |
483 | 24 |
Lipids (g) | Protein (g) |
19 | 54 |

69Raspberry, blueberry and melon smoothie

Photo credit: Thibaut Ruggeri.
70Serves 2
71Preparation time: 15 minutes
72Difficulty:

73Ingredients
■ 3 vanilla yoghurts
■ 100 g raspberries
■ 50 g blueberries
■ 200 g melon
74Place the raspberries, blueberries and the three vanilla yoghurts in a blender.
75Remove the seeds from the melon and peel it. Cut it into small cubes and add to the mixture.
76Start the blender, add one or two ice cubes, depending on the desired consistency.
77Serve chilled.
78Chef’s note
79This dessert covers almost half of the Dietary Reference Intake for vitamin C (40%). It also provides other elements that boost the immune system, including probiotics (yoghurt) and polyphenols (berries).
80Nutritional analysis per person
Energy (Cal) | Carbs (g) |
255 | 41 |
Lipids (g) | Protein (g) |
7 | 7 |
Notes de bas de page
1 Drinking cranberry juice every day particularly helps to fight against recurrent urinary infections..
Auteurs
PhD, Research Department – French Institute of Sport, Expertise and Performance (INSEP), Paris
PhD. Research Department – French Institute of Sport, Expertise and Performance (INSEP), Paris
Sports Traumatology Centre, Puteaux, France
PhD. Research Department – French Institute of Sport, Expertise and Performance (INSEP), Paris
Medical Department – French Institute of Sport, Expertise and Performance (INSEP), Paris
Le texte seul est utilisable sous licence Licence OpenEdition Books. Les autres éléments (illustrations, fichiers annexes importés) sont « Tous droits réservés », sauf mention contraire.
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