Intense Exercise Training and
Immune Function
Michael Gleeson and Clyde Williams
A person’s level of physical activity influences his/her risk of
infection, most likely by affecting immune function. Regular moderate exercise reduces the risk of infection compared with a sedentary
lifestyle, but very prolonged bouts of exercise and periods of intensified
training are associated with increased infection risk [1, 2]. Acute bouts
of exercise cause a temporary depression of various aspects of immune
function that will usually last for up to 24 h after exercise, depending
on the intensity and duration of the exercise bout. Several studies indicate that the incidence of symptoms of upper respiratory tract illness
(URTI) is increased in the days after prolonged strenuous endurance
events, and it has been generally assumed that this reflects the temporary depression of immune function induced by prolonged exercise.
More recently, it has been proposed that at least some of the symptoms of URTI in athletes are attributable to upper airway inflammation
rather than to infectious episodes [2]. Periods of intensified training
lasting a week or more have been shown to depress immune function,
and although elite athletes are not clinically immune deficient, it is
possible that the combined effects of small changes in several immune
factors may compromise resistance to common minor illnesses, particularly during periods of prolonged heavy training and at times of
major competitions.
The most common illnesses in athletes (and in the general population) are viral infections of the upper respiratory tract (i.e. the common
cold) which are more common in the winter months, and adults typically
experience 2–4 URTI episodes per year. Athletes can also develop similar symptoms (e.g. sore throat) due to allergy or inflammation caused by
inhalation of cold, dry or polluted air. In themselves, these symptoms are
generally trivial, but no matter whether the cause is infectious or allergic inflammation, they can cause an athlete to interrupt training, underperform or even miss an important competition [2]. Prolonged bouts of
strenuous exercise and periods of hard training with limited recovery
8
Increased exposure
to pathogens
Physiological stress
Psychological stress
Environmental stress
Inadequate diet
Lack of sleep
Lung ventilation
Skin abrasions
Foreign travel
Crowds
Increased risk of infection
Immunodepression
Fig. 1. Causes of increased infection risk in athletes.
and/or inadequate energy intake may compromise the body’s immune
system, reducing its ability to fight opportunistic infections [2]. Other
factors such as psychological stress, lack of sleep and malnutrition [3]
can also depress immunity and lead to increased risk of infection (fig. 1).
There are also some situations in which an athlete’s exposure to infectious agents may be increased, which is the other important determinant
of infection risk [4].
There are several behavioral, nutritional and training strategies
(fig. 2) that can be adopted to limit exercise-induced immunodepression and minimize the risk of infection [4]. Athletes and support staff
can avoid transmitting infections by avoiding close contact with those
showing symptoms of infection, by practicing good hand hygiene, oral
hygiene and food hygiene, and by avoiding sharing drinks bottles and
cutlery. Medical staff should consider appropriate immunization for
their athletes particularly when travelling to international competitions. The impact of intensive training stress on immune function can
be minimized by getting adequate sleep (at least 7 h per night is recommended), minimizing psychological stress, avoiding periods of dietary
energy restriction, consuming a well-balanced diet that meets energy
and protein needs, avoiding deficiencies of micronutrients (particularly
iron, zinc, and vitamins A, D, E, B6 and B12), ingesting carbohydrate
(30–60 g per hour) during prolonged training sessions, and consuming – on a daily basis – plant polyphenol (e.g. quercetin)-containing
supplements or foodstuffs (e.g. non-alcoholic beer) [5] and Lactobacillus probiotics [6]. Many other nutrition supplements, including
β-glucan, colostrum, echinacea, glutamine, zinc and others, are on sale
9
Prevent transmission
of pathogens
Maintain robust
immune function
t Effective management of
training microcycle
t Good hand hygiene
t Avoid infected persons
t Adequate recovery
t Avoid hand contact with
eyes/nose/mouth
t Avoid sharing personal items
t Ensure cleanliness in living
and eating areas
t Good food hygiene
t Limit contact with door
knobs and other frequently
handled items
t Avoid micronutrient
deficiencies
t Avoid crash dieting
t Ingest carbohydrate during
prolonged training sessions
t Get adequate sleep
t Daily probiotic
t Limit other sources of
life stress
Reduced risk of infection
Fig. 2. Strategies to limit the risk of infection in athletes.
with claims that they can boost the immune system, but there is no
strong evidence that any of these are effective in preventing exerciseinduced immune depression [6].
References
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2
3
4
5
6
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Gleeson M (ed): Immune Function in Sport and Exercise. Edinburgh, Elsevier, 2005.
Walsh NP, Gleeson M, Shephard RJ, et al: Position statement part one: immune function and exercise. Exerc Immunol Rev 2011;17:6–63.
Shetty P: Nutrition, Immunity and Infection. Cambridge, CABI Publishing, 2010.
Walsh NP, Gleeson M, Pyne DB, et al: Position statement part two: maintaining
immune health. Exerc Immunol Rev 2011;17:64–103.
Scherr J, Nieman DC, Schuster T, et al: Non-alcoholic beer reduces inflammation and
incidence of respiratory tract illness. Med Sci Sports Exerc 2012;44:18–26.
Gleeson M: Exercise, nutrition and immunity; in: Calder PC, Yaqoob P (eds): Diet,
Immunity and Inflammation. Cambridge, Woodhead Publishing, 2012, chapter 30.