Many people think that athletes are the healthiest human beings in the planet. However, fitness does not necessarily equal health. High level performance can take a toll in athletes and their immune system.
Regular moderate exercise mitigates inflammation and all the health conditions caused by it. However, a large volume of high intensity exercise combined with travel and stress can depress the immune system and lead to illness (1).
The following factors have an impact on the immune system in the context of athletic activities:
When energy intake is not enough to match energy output, immune function can be compromised. This is a common problem for athletes who need to make a specific weight class (2).
Older athletes who exercise with lower intensity and duration need to adjust their energy intake accordingly to avoid gaining excess body fat (1).
Carbohydrate restriction can depress the immune system as a drop in blood glucose causes cortisol – the stress hormone – to increase (2).
It seems that the optimal time for carbohydrate consumption (as it relates to immune function restoration) is during prolonged intense exercise. There is no need to increase carbohydrate beyond usual requirements during other types of exercise nor at other times (1).
Older athletes may benefit from a lower carbohydrate intake to match the natural decline in glucose tolerance and insulin sensitivity (1).
The long-chain omega-3 fatty acids EPA and DHA can decrease inflammation, muscle damage and soreness, and improve immune function (1).
Athletes should meet their protein requirements, which are higher than for non-athletic individuals, for muscle synthesis and immune function. There is some indication that branched-chain amino acids (BCAAs) can counterbalance immune function depression due to exercise (1).
Although most vitamin D is not obtained from our diets, I’ve included this important hormone/vitamin in this section just because we can get it from food.
Vitamin D is important for gene expression modulation of the immune system. Inadequate vitamin D levels is associated with incidence of upper respiratory infections (URIs) (1).
Recommendations for athletes include supplementing 1000 UI/day of vitamin D3 if serum 25-Hydroxy Vitamin D is < 50 nmol/L during the winter months (2). However, athletes with levels > 75 nmol have the lowest risk of contracting URIs. With this consideration, the dose could be increased to up to 4000 UI/day during the winter months if serum vitamin D is < 75 nmol/L (1).
There is some evidence that vitamin C supplements may prevent URI symptoms (2).
There is some evidence that probiotics can decrease URI symptoms (2).
Zinc is essential for multiple body processes, including immune function. Athletes might be at risk of deficiency due to inadequate intake and losses in sweat and urine (1).
There is some evidence that zinc acetate lozenges (75mg) can decrease the duration of URI symptoms (1, 2).
Magnesium is important for proper immune function. Athletes who are deficient in magnesium are at risk of a larger weakening of immune function due to exercise (1).
Iron is important for proper immune cell development and function. Iron deficient athletes are at risk of infection and thus should supplement iron + vitamin C as a preventative measure. However, iron supplementation during infection is not recommended (1).
Antioxidants, including vitamins E, C and A, reduce oxidative stress, are important for immune function and may improve recovery (3).
For most athletes, eating a healthy nutrient-dense diet should be enough to cover their antioxidant needs. Supplementation is only recommended for athletes who have low levels. Moreover, it is important to consider that antioxidant supplementation may prevent certain exercise-induced adaptations (1).
Because inflammation and oxidative stress increase with age, older athletes should consume a large volume of antioxidant-containing foods (1).
There is some evidence that echinacea supplements may lower symptoms of URIs but cannot prevent infection (1).
Like antioxidants, polyphenols are present in many plant foods. Polyphenols may assist in reducing inflammation and oxidative stress among other negative health effects. Again, like antioxidants they should preferentially be obtained from the diet (1).
Probiotics modulate the immune system in multiple ways, however there is no consensus about the recommended dose or mix of strains (1).
Colostrum is the fluid that mammal mothers produce within a few days of giving birth. It is rich in antibodies and other immune factors. There are some studies that suggest that colostrum from cows may reduce URI symptoms in athletes (1).
Intense and prolonged exercise has been associated to a decrease in immune function and greater incidence of URIs, particularly during winter (1). In fact, it’s well known that marathon and ultra-marathon runners are at increased risk of URIs (4). Therefore, it’s important to write training programs smartly managing intensity and volume to allow for adequate recovery (2, 4).
Exercising in the cold might be detrimental as this environment allows the replication of a virus that causes the common cold. However short exposures to cold environments (e.g. in hot-cold showers) might enhance immune function (2).
Training at high altitude and low oxygen might also decrease immune function and increase URI symptoms (2).
Athletes may be subjected to stress from many sources, including their personal circumstances and team, training and competition factors. Chronic stress impairs the immune response, so it is important for athletes to learn how to manage and attenuate all forms of stress through mindfulness, meditation or other means (2).
Poor sleep is associated with inflammation and may lead to increased risk of infections, cardiovascular disease, cancer and decreased immune responses. Unfortunately, athletes seem to have poor sleep patterns compared to the general population (2). On the other hand, sufficient sleep may improve athletic performance (2, 3) and is important for training adaptations and recovery (3).
For more on sleep check out my review of Matthew Walker’s Why We Sleep.
Athlete face physical and psychological demands that may compromise their immune system, making them more susceptible to infection and illness. This can be managed by avoiding over-training, eating a healthy diet, managing stress and getting appropriate sleep. This is the same advice for the general population, but training and competition represent extra challenges for the athletic population. A good team, including a Sports Dietitian can help athletes navigate these challenges.
Additional recommendations include:
- Avoid being around sick people
- Keep hands clean and get vaccines when required
- Avoid touching eyes, nose and mouth
- Don’t train or compete when sick (1, 4)
- Walsh NP. Recommendations to maintain immune health in athletes. European journal of sport science. 2018;18(6):820-31.
- Bermon S, Castell LM, Calder PC, Bishop NC, Blomstrand E, Mooren FC, et al. Consensus Statement Immunonutrition and Exercise. Exercise immunology review. 2017;23:8-50.
- Doherty R, Madigan S, Warrington G, Ellis J. Sleep and Nutrition Interactions: Implications for Athletes. Nutrients. 2019;11(4).
- Castell LM, Nieman DC, Bermon S, Peeling P. Exercise-Induced Illness and Inflammation: Can Immunonutrition and Iron Help? 2019;29(2):181.
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