Moderate amounts of exercise are considered protective as they activate immune system cells, eliminate infections agents, and reduce the inflammatory response of injured muscle (1). However, prolonged exercise at high intensity and long durations can be detrimental to our immune systems. This results in changes to our immune cell activity, increase the risk of immune depression and result in a window of increased infection susceptibility (1). This is known as the J curve: regular moderate amounts of exercise are beneficial to our immune systems, whilst prolonged intense training can render immune systems to the same levels of inactive or moderately active individuals (1).
How Does Intense Exercise Lead to A Supressed Immune System?
Prolonged exercise at a heavy, intense level, can suppress immune systems through (1):
- A decrease in the activity of white blood cells / natural killer cells which reject infected cells
- A reduction in T cell function, an important white blood cell
- A decrease in Salivary IGA, an antibody critical for immune function of mucous membranes,
- An increase in pro inflammatory cytokines which are small proteins secreted by immune cells
- An increase in pro inflammatory chemokines, cytokine cells which attract immune cells to the site of an infection to target and destroy microbes.
- An increase in oxidative stress in response to the immune system falling under stress
- Psychological stress from training and competition can suppress our immune system
- Adrenal Fatigue, where hormones levels produced by the adrenal glands are depleted or insufficient to handle the heightened stress of endurance training
The “Window” Of Immune Suppression After a Long Training Session
This window of immunosuppression after intense prolonged exercise can last up to 72 hours after exercise concludes, especially when the exercise is continuous, prolonged (1.5 hours or more), of moderate to high intensity (55–75% maximum O2 uptake), and performed without food intake (1). Periods of intensified training (overreaching) lasting 1 week or more may result in longer lasting immune dysfunction and suppression (1). During these heavy and intense training situations, there is also dietary energy deficiency, sleep deprivation, and stress further inducing immune suppression.
Upper Respiratory Infections
Upper Respiratory infections or symptoms are common amongst elite athletes. There is an established link between training load and respiratory illness including chest colds, chest infections or pneumonia (1). Endurance athletes need to balance training loads to avoid the risk of fatigue, illness, injury and avoid over training (1). Upper respiratory infections do not need an underlying infection. Stress on the lungs, dehydration and prolonged exposure to irritants (pollutants, allergens) can also induce airway injury causing infections.
The Benefits Of Antioxidants For Immunity
Athletes on a high antioxidant diet may be able to increase their protection against training and pollution induced respiratory illness (1). Inflammation is linked to the large number of respiratory symptoms reported by elite athletes. The nutrient rich properties of foods high in antioxidants, such as fruit and vegetables, can also have anti-inflammatory effects on the airway and respiratory functions, reducing airway inflammation (1). A diet rich in antioxidants can also counter the elevated levels of free radicals produced from intense and prolonged exercise. Antioxidants scavenge free radicals and convert them into unreactive substances, so they can’t damage our body’s cells.
Eat a Diet Rich in Immune System Vitamins
Eating plenty of fresh whole foods high in the following nutrients will boost your immune system:
- Zinc – red meat, chicken, fish, dairy foods, eggs, legumes and sunflower and pumpkin seeds
- Vitamin C – (Citrus fruits, kiwi fruit, strawberries, broccoli, cabbage and parsley)
- Garlic – heat can destroy some of its immunity properties so add it raw to a salad dressing
The Benefits Of Carbohydrates Before and During Long Intense Training Sessions
The impact of inadequate carbohydrate intake on the immune system is well researched (1). This can induce various responses in the immune system such as increased cortisone hormones, decreased immune fighting cells and increases in pro-inflammatory cytokines and proteins (1). Studies have shown that sufficient carbohydrate intake, of 30-60g/hour during long training sessions, can lessens the above detrimental effects on the immune system.
Training in a glycogen depleted (fasted) state can be beneficial for low duration or intensity training can be useful for improving immunity, however for high intensity and duration training this can lead to a negative impact on stress hormones and reduced immunity (1). Eat carbs before and during your long or intense training rides!
Gut Health and Immunity
Many studies show the connection between immunity and gastrointestinal function (1). Endurance sport can cause increased damage to the gut. Avoiding high sugar refined carbohydrates and gluten and sticking with wholegrains and unprocessed carbs can preserve your gut lining. Good quality protein intake during recovery, especially in the form of the amino acid glutamine is recommended (1). Glutamine is a fuel source for immune fighting cells and becomes depleted during intense prolonged exercise. A fall in intestinal glutamine levels can lead to bacteria and other toxins making it across the intestinal membrane which can cause immune system failure (1). Foods high in glutamine include fish, legumes, raw cabbage, raw beetroot and other meats. Heat during cooking can destroy Glutamine. Other sources are protein recovery powders including glutamine.
Overtraining and Immunity
Overtraining is when exercise causes stress and physical damage to your body at a rate faster than your body can repair the damage (2). It is often accompanied by poor immunity, increased rates of illness, fatigue and poor performance during training, insomnia, depressed mood state, lack of appetite, and general feelings of fatigue in the morning (2). Adrenal fatigue can be a component of this. If you are demonstrating these symptoms, just taking a week off exercise can make a big difference to your recovery and long term athletic performance (2).
Overtraining can be avoided by allowing for sufficient recovery after and between long training sessions; allowing for enough rest days per week during intense training; by ensuring that nutritional guidelines are followed during and after exercise during recovery, especially carbohydrate during prolonged exercise; and by obtaining sufficient sleep and a general reduction in stress (2). Dialing back your exercise one week a month can also be beneficial (2).
- Gleeson, Michael. “Immune function in sport and exercise.” Journal of applied physiology2 (2007): 693-699.
- Halson, Shona L., and Asker E. Jeukendrup. “Does overtraining exist?.” Sports medicine14 (2004): 967-981.