European Journal of Physical Education and Sport Science
ISSN: 2501 - 1235
ISSN-L: 2501 - 1235
Available on-line at: www.oapub.org/edu
Volume 3 │ Issue 2 │ 2017
doi: 10.5281/zenodo.439551
THE EFFECTS OF STRENUOUS EXERCISE AND NUTRITION ON
THE IMMUNE FUNCTIONS OF ELITE ATHLETES
Thaer Jabbar Ashour1i,
Cherifi Ali2,
Hala Mikhael Youssef3
University Manouba, High Institute of Sport and
1
Physical Education of Ksar-Saïd, Tunis, Tunisia
University Algeria, Institute of Sport and
2
Physical Education, Alger, Algeria
Lebanese University, Faculty of Education,
3
Department of Physical Education, Lebanon
Abstract:
The intense activities carried out by athletes result in them undergoing acute and
chronic stress and this in turn will suppress their immune system as well as increase
their oxidative species generation. On top of that, these athletes has a tendency to
consume less calories than what is needed and they also have a tendency to avoid
consuming fats, and the latter action may affect their immune system and anti-oxidant
mechanisms. The stress caused by the exercise is dependent upon how intense the
exercise is and its duration, and it is relative to the athlete s maximum capacity. The
depletion of glycogen in the muscles affects the performance of the exercise as well as
increases the stress. However, the glycogen stores can be protected if there is an
increase in fat oxidation (glycogen sparing). Athletes should have balanced diets
whereby the total calories consumed is the same as that expended and the
carbohydrates and fats that are utilized must be replenished. However, many athletes
fail to meet these important basic criteria thus compromising their glycogen or fat
stores, and do not consume sufficient essential fats and micronutrients which are
required to maintain their intense exercise, immune competence and anti-oxidant
defense. Over-training or malnourishment may result in an increased risk of infections.
In some cases, the intake of micronutrient supplements may strengthen the immune
system and make up for the deficiency of the essential nutrients. Any nutrient
Copyright © The Author(s). All Rights Reserved.
© 2015 2017 Open Access Publishing Group
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deficiencies in the athletes diet must be compensated with nutritional supplements, but
it must not be over compensated. If the above-mentioned rules are complied with and
the training are properly regulated so that there is no overtraining, the immune system
can be maintained at the optimal level and this in turn will reduce the risk of diseases.
.
Keywords: immunity, nutrition, training, exercise, leukocytes
1. Introduction
Tough, prolonged and heavy exercise regimes are often linked to the lowered immune
functions of cells. In addition to that, insufficient nutrition or malnutrition can
compound the negative effects of heavy exertion on immuno-competence. Diet lacking
in proteins and specific micronutrients are known to have caused immune
dysfunctions. A diet that contains sufficient zinc, iron and vitamin A, E, B6 and B12 is
vital for the body s immune system to function properly although excessive intake of
specific micronutrients can weaken the immune system and have a negative effect on
health. Excessive intake of fats has also been known to weaken the immune system. As
such, in order to maintain proper immune functions, athletes must consume a wellbalanced diet that is able to meet their energy requirements (Alexander et al, 1985). Any
athlete that exercises when his body is in a carbohydrate-depleted state will have more
stress hormones in their blood circulatory system and several of their immune function
indices will indicate that the body is in distress. On the other hand, the consumption of
30
60 grams of carbohydrate h71 when a person is carrying out continuous intensive
exercise reduces the rise of stress hormones like cortisol and also constrain the amount
of immune depression that is induced by exercise. However, there is insufficient
convincing evidence to show that the much touted immune-boosting supplements
like vitamins with anti-oxidant properties, glutamine, probiotics, zinc and Echinacea
can prevent exercise-induced immune impairment (Peters et al, 1993).
2. The immune function of athletes
The function of the immune system is to recognize, attack, destroy and protect the body
from foreign elements in the body. Basically, the immune system can be split into two
broad functions namely, innate (non-specific and natural) and acquired (specific and
adaptive) immunity and both of the work together synergistically. Any attempt by a
foreign infectious agent to trespass into the body will immediately activate the innate
system. The body s first line of defense consists of three general mechanisms with a
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THE EFFECTS OF STRENUOUS EXERCISE AND NUTRITION ON
THE IMMUNE FUNCTIONS OF ELITE ATHLETES
shared common goal of preventing micro-organisms from entering the body and they
are: (1) physical or structural barriers (skin, the linings of the epithelia, mucosal
secretions); (2) chemical barriers (the acidity or alkalinity of bodily fluids and soluble
factors such as lysozymes and complement system); and (3) phagocytic cells (e.g.
neutrophils and monocytes or macrophages). If the innate system fails, the resulting
infection will activate the acquired system which will then aid in the recovery from the
infection. The monocytes or macrophages will ingest and process the foreign microorganism, and will then present it (antigens) to the lymphocytes. This is immediately
followed by the clonal multiplication of T- and B- lymphocytes that have receptors that
are able to recognize the antigen, thus producing specificity and memory
which
enables the immune system to mount a strengthened cell-mediated and humoral
response as and when the body is re-infected by the same pathogen. The production of
cytokines including interleukins, interferons and colony-stimulating factors are vital for
the activation and regulation of the immune functions (Nieman et al, 1990). An
important characteristic of the immune system is the involvement of several
functionally different types of cells that enables many types of defense mechanisms.
Therefore, to assess the status of the various immune functions would require a
thorough methodological approach whereby the target is a wide spectrum of immune
system parameters. However, at the moment there are no instruments that can predict
the cumulative effects of the many tiny changes in the immune system s parameters of
the body s resistance to infections Mackinnon et al,
. ‚n athlete s heavy training
and competition schedule can impair the immunity of the athlete and result in an
increase in susceptibility to infections, specifically upper respiratory tract infections
(URTI) (Mackinnon et al, 1997). This particular exercise-induced dysfunction of the
immune system appears to be mainly caused by the immuno-suppressive actions of
stress hormones like cortisol and adrenaline. Nutritional deficiencies can also weaken
the body s immune functions and there are ample evidences to link the prevalence or
severity of many infections with specific nutritional deficiencies (Barrett et al, 2002).
However, there is also evidence to show that excessive ingestion of individual
micronutrients (e.g. n-3 polyunsaturated fatty acids, iron, zinc, vitamins A and E) can
weaken the immune function, thereby increasing the risk of infection. It is commonly
known to most athletes that even infections that are considered to be medically
harmless can cause a drop in the athlete s performance Pedersen et al,
.
3. Avoiding nutrient deficiencies
The key to having an immune system that is effective is to ensure that you consume
sufficient nutrients that are essential for triggering the body s immune system together
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with its interactions, differentiations or functional expressions. Malnutrition weakens
the immune systems defenses against foreign pathogens resulting in an individual
becoming more susceptible to infections. Some pathogens may affect an individual s
nutritional status through the suppression of appetite, poor nutrient absorption, higher
nutrient requirements and greater losses of endogenous nutrients (Beals et al, 1994).
It is a widely accepted fact that insufficient intake of proteins weakens the
immunity of the host as it harms the T-cell system and leads to an increase of
opportunistic infections (Beals et al, 1994). The fact that protein deficiency weakens
immunity is not surprising because the immune system s defenses rely on rapid cell
replication and the production of proteins like immunoglobulins, cytokines and acute
phase proteins. In humans, protein-cum-energy malnutrition leads to the deficiency of
mature and fully differentiated T-lymphocytes as well as in vitro proliferative response
to mitogens, although the second effect is reversible with nutritional repletion (Bassit et
al, 2002). In addition to that, in a situation where there is protein-cum-energy
malnutrition the T-lymphocytes CD4+/CD8+ (helper/suppressor cells) ratio is
significantly decreased and the phagocytic cell functions, production of cytokines and
complement formation are all reduced. Basically, protein-cum-energy malnutrition in
humans affects all forms of human immunity and the severity is dependent upon the
protein deficiency in relation to the energy intake. It is unlikely for athletes to suffer
from extreme malnutrition unless his dieting is very severe, but some impairment to the
defense mechanism has been seen in cases whereby the protein deficiency is moderate
(Bishop et al, 1999).
Among the athletes, the individuals that are exposed to the highest risk of
protein deficiency are those that are on weight-loss programs, vegetarians and having
unbalanced diets (e.g. consuming carbohydrates that are disproportionately higher than
their total protein intake). Generally, protein and energy deficiencies are accompanied
by micronutrient deficiencies. Energy-restricted or low carbohydrate diets are
commonly found in sports where being lean or having a low body mass is associated
with having a performance or aesthetic advantage (e.g. endurance running, figure
skating or gymnastics) or is necessary so as to fall within certain body weight criteria
(e.g. boxing and weightlifting). Subsequently, this has led to the discovery of anorexia
athletica, a new subclinical eating disorder and it is linked to an increase in
susceptibility to infection. It has been found that even short-term dieting has an
influence on the immune system in athletes, for e.g. a loss of 2 kg of body weight over a
period of 2 weeks has an adverse effect on macrophage phagocytic functions (Nieman,
1997).
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Moreover, for the immune system to function normally certain vitamins must
be available. Any deficiency of fat-soluble vitamins like vitamin A and E as well as
water-soluble vitamins like vitamin B6, B12, C and folic acid can harm the body s
immune functions and reduce its resistance to infections (Bishop et al, 2001). If the
vitamin deficiencies are corrected (through the intake of vitamin supplements), the
body s immune functions will return to normal Peters, 1996). In addition to that, some
minerals are able to modulate the effects of the immune functions and it includes
copper, iron, magnesium, manganese, selenium and zinc, but other than zinc and iron,
the isolated deficiencies are very infrequent. Field studies have regularly shown that
iron deficiency is associated with higher morbidity from infectious diseases (Pedersen
et al, 2003). It has been shown that exercise has a noticeable effect on the metabolism of
iron and zinc and as such, the requirements of such minerals are definitely higher in
athletes as compared to individuals who lead a sedentary live because a lot of the
minerals are excreted through sweat and urine. On the other hand, having too much
minerals, like iron and zinc, can harm the body s immune system and the person can
become more susceptible to infections (Coutsoudis et al, 1992). As such, supplements
should only be taken as and when it is required and it is good to monitor the iron
(serum ferritin and hemoglobin) and zinc status (erythrocyte zinc). Research on the
intake of zinc as a supplement to treat common cold has been carried out in not less
than 11 studies and the results of the studies have been published since 1984.
The results of the studies have been vague or unclear and the latest reviews of
the matter are of the opinion that more research in the field must be carried out before
zinc supplements can be recommended as a treatment for the common cold. There is
not much evidence to show that zinc supplements can actually reduce incidences of
URTI, but the available studies have indicated that for zinc to have any beneficial effect
in treating the common cold i.e. a reduction of the symptom s duration and/or severity
it must be ingested within 24 hours of the appearance of the common cold symptoms.
The potential side effects of zinc supplements include nausea, reduction of high-density
lipoprotein, bad or different taste, the decline of some immune cell functions (e.g.
neutrophil oxidative burst) and distortion of the absorption rate of copper (Pedersen et
al, 1989).
3.1 Eating the right food and types of fat
Comparatively, not much is known of dietary fatty acids role in the regulation of
exercise-induced alteration of the body s immune functions. Two types of
polyunsaturated fatty acids (PUFA), namely the omega-6 and omega-3 series (both are
derived from linoleic acid), are essential to the body but they cannot be synthesized by
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the body and hence has to be derived from the diet. Reports show that diets having
either omega-3 or omega-6 can alleviate the conditions of patients suffering from an
over-active immune system like rheumatoid arthritis because the said two
polyunsaturated fatty acids have anti-inflammatory effects (Gleeson et al, 2004). Some
researchers advocate that high consumption of arachidonic acid as compared to the
intake of fatty acids from the n-3 group may have undesirable effects on the
inflammation and immune functions both during and after exercise (Eskola et al, 1978).
But, a recent study has indicated that n-e PUFA supplementation does not have any
influence on the exercised-induced increase of pro- or anti-inflammatory cytokines
(Kinsella, 1987). There is a need to conduct further research on how the immune
functions are affected after exercise or during heavy training sessions if the intake of
essential fatty acids are altered. A recent study that examined the effects of a 7-week
endurance training based on a carbohydrate-rich diet (65% of dietary energy are
derived from carbohydrates) and fat-rich diet (62% of dietary energy are derived from
fats) has indicated that the composition of the diet during the training period can
influence the natural immunity because the carbohydrate-rich diet has increased
natural killer (NK) cell activities as compared to that of the fat-rich diet. The conclusion
that can be drawn from this research indicates that a fat-rich diet is harmful to immune
functions as compared to that of a carbohydrate-rich diet; however, it could not
ascertain whether the said effect is caused by insufficient dietary carbohydrate or a
surplus of a specific dietary fat component (Toft et al, 2000).
3.2 The body's need for vitamins
A moderate increase in the intake of certain vitamins (like vitamins A and E) above the
recommended amounts may improve the immune functions of very young or elderly
persons (Venkatraman and David , 2002), but perhaps it does not have the same effect
in young adults. However, the consumption of extremely large doses of specific
vitamins, which is a fairly common practice amongst athletes, and damage the immune
functions as well as having other toxic effects (Coutsoudis et al, 1992). For instance, a
daily dosage of 300mg of vitamin E consume by men for a period of 3 weeks has
resulted in significant depressed phagocytic functions and lymphocyte proliferation
(Fogelholm, 2008). A recent study has shown that participants of an Ironman triathlon
who took 600 mg of vitamin E daily for 2 months before the race have elevated
oxidative stress as well as inflammatory cytokine responses during the race as
compared to those given placebos for the same duration (Peake et al, 2007). Whereas
elderly people (n = 652) who were on a daily dosage of 200 mg of vitamin E
supplements had more severe infections which includes the total duration of the illness,
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fever as well as being restricted from carrying out physical activities. A recent study
whereby patients with ischaemic heart disease that were given 600 mg per day of
vitamin E had no effects on all-cause mortality or an increase in the number of deaths as
compared to those that were given placebos. Mega dosages of vitamin A can damage
the inflammatory responses and complement formation together with other
pathological effects like an increased risk of foetal abnormalities in pregnant women
(Gleeson et al, 2007).
Vitamins that have anti-oxidant properties such as vitamins A, C, E as well as
beta-carotene (pro-vitamin A) may be required in larger amounts by athletes in order to
deactivate the by-products of exercise-induced lipid peroxidation (Philipset et al, 2013).
But, there are no conclusive data to show that nutritional anti-oxidants have any effect
on muscle damage or a delayed onset of muscle tenderness. An increase in the
production of oxygen free radicals caused by the spectacular increase in oxidative
metabolism during exercise has the potential to inhibit immune responses (Nikolaidis et
al, 2008).
4. Dietary manipulation to reduce the immune weaknesses
Elevated concentrations of stress hormones can caused exercise-induced immune
functions and as such effective nutritional strategies can lessen the stress hormone
response to exercise should be implemented so as to control the severity of exerciseinduced immune dysfunction. There is definitely sufficient experimental evidence to
back this notion, even though it is unclear whether the magnitude of such effects is
enough to affect infection risk (Pedersen and Laurie, 2000).
4.1 Carbohydrate intake before and during exercise
In the last few years, a few research have studied how dietary carbohydrate affects
hormonal and immune responses to exercise. These research (Mitchell et al, 1998) have
discovered that if the individuals perform long-drawn-out exercises over a period of a
few days when they have very low carbohydrate diets (usually 5
10% of their dietary
energy intake are from carbohydrates), the level of the stress hormones (like adrenaline
and cortisol) and cytokine (like IL-6, IL-1ra and IL-10) response is significantly higher
than when they are subjected to normal or high carbohydrate diets. There are
conjectures about athletes on insufficient carbohydrate diets putting themselves at risk
from the acknowledged immunosuppressive effects of cortisol, as well as the repression
of antibody production, natural killer cell cytotoxic activities and lymphocyte
proliferation. It has been observed that when a person is exercising (1 h at 75% V O2
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max) when he is in a glycogen-depleted state (caused by prior exercise and 2 days of
low carbohydrate diet) his circulating lymphocyte numbers 2 hours after the exercise is
much lower than when the same exercise was performed after 2 days of high
carbohydrate diet. But, the management of the carbohydrate status did not have any
effect on the reduction in mitogen-stimulated lymphocyte proliferation that occurred
post-exercise (Nehlsen et al, 1997).
The ingestion of carbohydrates during exercise also reduces the increase in
plasma catecholamines, adrenocorticotrophic hormone, cortisol, growth hormone and
cytokines (Gleeson, 2007). Consuming carbohydrates during exercise also weakens the
transferring of most leucocyte and lymphocyte subsets as well as the rise in the
neutrophil (as the lymphocyte ratio blocks the exercise-induced drop in neutrophil
function) and decreases the extent of the attenuation of mitogen-stimulated Tlymphocyte proliferation after prolonged exercise (Mitchell et al, 1998). In recent times,
it has been shown that the consumption of 30
60 grams of carbohydrate h71 when
cycling strenuously for 2.5 hours prevented the fall in the number and percentage of
interferon-g-positive T-lymphocytes and suppressed interferon-g production from
stimulated T-lymphocytes in placebo control trials (Henson et al, 1999). The production
of interferon is important for the anti-viral defense and researchers have opined that the
repression of interferon-g production can lead to an elevated risk of infection after
prolonged exercise sessions (Hemmi et al, 2002).
Although carbohydrate intake during exercise is apparently effective in the
minimization of some of the immune disquiets associated with lengthy continuous and
strenuous exercise, it seems to be less effective for lighter intermittent exercises, like in
football or rowing training sessions (Gleeson, 2013). It is also obvious that carbohydrate
feeding is less effective in the reduction of immune cell trafficking and functional
depression in situations whereby continuous extended exercise is performed until the
person is fatigued. The ingestion of carbohydrates before the exercise does not appear
to be very effective in controlling exercise-induced leukocytosis or depression of
exercise, nourishment and immune neutrophil function (Gunzer et al, 2012). Currently,
there is no evidence to show that the useful effect of ingesting carbohydrates on
immune responses to exercise gives rise to lower incidences of URTI after extended
exercise such as marathon races. Although carbohydrate ingestion has been shown to
have beneficial effect on post-race URTI in a study of 98 marathon runners, the study
sample is statistically insignificant and bigger-scale studies must be carried out to
investigate this possibility (Gleeson et al, 2001).
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4.2 Fluid intake during exercise
The intake of beverages when exercising not only prevents dehydration (which is
linked to an increase in stress hormone response) for it also helps to sustain the saliva
flow rate when the person is exercising. The contents of saliva includes several types of
proteins with anti-microbial properties such as immunoglobulin-A (IgA), a-amylase
and lysozyme. The secretion of saliva normally falls during exercise and regular intake
of fluids during exercise has been found to prevent this effect and this has been
confirmed by a recent study that shows regular intake of lemon-flavored drinks
containing carbohydrates help to maintain saliva flow rate and this means that saliva
IgA secretion rate is maintained during prolonged exercise as compared to a restricted
fluid intake regimen (Bishop et al, 2000).
5. Dietary immunostimulants
Beta-carotene (pro-vitamin A) is both an anti-oxidant and an immunostimulant, and it
has been shown to increase the number of T-helper cells in healthy humans as well as
stimulate natural killer cell activity when it was added to in vitro human lymphatic
cultures (Chew and Jean, 2004). Furthermore, it has been reported that elderly men that
have been taking beta-carotene supplements at a dosage of 50 mg on alternate days for
about 10 to 12 years have significantly higher natural killer cell activity when compared
to another group of elderly men that were consuming placebos. But, the consumption of
beta-carotene supplements by runners did not have any significant effect on the
incidences of URTI after they have completed a 90 km ultra-marathon. In addition to
that, smokers are advised not to consume more than 7 mg of supplements a day
because there is a possible increase in risk of lung cancer in this group of people
(Northoff et al, 1998).
Some herbal preparations are known to have immunostimulatory effects and
many athletes are consuming products that contain Echinacea purpurea. But, not many
controlled studies have been carried out to examine how dietary immunostimulants
affect the exercise-induced changes in the immune system. A recent double-blind
placebo-controlled study was carried out to study the effect of a pre-treatment daily
dose of Echinacea purpurea juice on 42 triathletes 28 days before a race. A sub-group of
athletes, treated with, was used as a reference and the participants were supplied with a
micronutrient supplement that is vital for optimal muscular functions. The most
striking finding during the said pre-treatment period was that not a single athlete from
the E. purpurea group fell ill as compared to 3 and 4 individuals from the magnesium
and placebo group respectively. It appears that pre-treatment with E. purpurea reduces
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the release of soluble IL-2 receptors both before and after the race and there was an
increase in the exercise-induced increase in IL-6 (Northoff et al, 1998).
Several experiments have shown that E. purpurea extracts truly shows that there
are significant immunomodulatory activities. Amongst some of the pharmacological
properties that have been reported is that there is convincing evidence to support
macrophage activation (Haddad et al, 2005). Phagocytotic indices as well as
macrophage-derived cytokine concentrations were shown to be Echinacea-responsive
in many assays and there were sufficient evidence to indicate that polymorphonuclear
leucocytes and natural killer cells were activated. There were also changes in the
numbers as well as activities of T- and B-lymphocytes, but its certainty is less. In spite of
cellular evidence of immunostimulation, the description of the pathways that lead to
enhanced resistance to infectious diseases are inadequate. Many dozens of experiments
carried out on humans, including a few blind randomized ones, have shown health
benefits, and the strongest data are from trials using E. purpurea extracts to treat acute
URTI. Even though the trials indicate that there are modest benefits, but the said trials
had limitation in both size and methodological quality. However, a recent randomized
double-blind
placebo-controlled
study
whereby
unrefined
Echinacea
were
administered at the onset of URTI to 148 college students did not show and obvious
benefit or harm as compared to those given placebos (Barrett et al, 2002). Therefore,
although there are a lot of reasonably good quality scientific data on Echinacea, its
efficacy in the treatment of illness or the enhancement of human health has not been
proven beyond a reasonable doubt. There is now a fairly large body of evidence to
show that if probiotics, a food supplement that has friendly gut bacteria, is consumed
regularly it can change the population of the micro-flora in the gut and affect changes in
the immune functions of the gut. Studies have indicated that the intake of probiotic can
improve the rate of recovery of patients suffering from rotavirus diarrhea, have better
resistance to enteric pathogens as well as promote anti-tumor activities. That is also
evidence to show that probiotics can alleviate some allergic and respiratory conditions
in young children. However, as at this point in time there have not been a single
published study on how effective the probiotics are when used by athletes (Isolauri et
al, 2001).
6. Conclusions
1. Heavy exercise and nutrition have their own distinct influences on immune
functions and the influences are stronger when the exercise stress and poor
nutrition are acting synergistically.
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2. Diets that are deficient in energy, protein and specific micronutrients are linked
to weakened immune functions and higher susceptibility to infection. Sufficient
consumption of iron, zinc and vitamins A, E, B6 and B12 are vital for the
maintenance of the immune functions. Athletes are advised to always consume
sufficient micronutrients.
3. To ensure that their immune functions are at an optimum level, athletes must eat
a well-balanced diet that is sufficient to meet their energy demands. They should
also make sure that they consume sufficient amounts of protein and
micronutrients.
4. The following of energy-restricted diets to consume vitamin supplements.
5. Athletes that exercised in a carbohydrate-depleted state will have bigger
increases in circulating stress hormones as well as a greater perturbation of some
immune function indices.
6. Persons performing extended exercises are advised to consume carbohydrates
(30
60 grams h71) in their drinks as it can weaken some of the
immunosuppressive effects of prolonged exercise. However, there is no evidence
to support this assertion.
7. It is not advisable to consume mega-doses of vitamins and mineral because the
excessive intake of some micronutrients (iron, zinc, vitamin E) can harm the
body s immune functions.
8. Fat-rich diets can suppress some features of the immune cell function.
9. There are insufficient evidence to support the so-called immune-boosting
supplements like high dosages of anti-oxidant vitamins, glutamine, probiotics,
zinc and Echinace that is supposed to prevent exercise-induced immune
impairment. Current available evidence on the efficacy of Echinacea extracts,
probiotics and zinc lozenges in the prevention or treatment of common infections
is scarce and as such, there is no recommendation on the use of these
supplements.
10. It is arguable whether antioxidant supplements are required or desirable for
athletes. Evidence of the effects of high dosages of vitamin C in the reduction of
post-exercise incidences of URTI are conflicting and there is no evidence to show
that this practice can actually prevent exercise-induced immune impairment.
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THE EFFECTS OF STRENUOUS EXERCISE AND NUTRITION ON
THE IMMUNE FUNCTIONS OF ELITE ATHLETES
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THE EFFECTS OF STRENUOUS EXERCISE AND NUTRITION ON
THE IMMUNE FUNCTIONS OF ELITE ATHLETES
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