Inflammatory response in endurance athletes
Endurance athletes, including cyclists, runners, swimmers and triathletes, are required to exercise intensely and/or for prolonged periods each week when training for competitions. Whilst moderate exercise appears to have a preventative effect against URTIs, there is a correlation between an increase in training volume and intensity and the occurrence of URTIs, particularly after training and competition, due to temporary suppression of the immune system – the “open window” (4). This can undesirably disrupt the athlete’s training schedule and competitions. Several mechanisms may explain this “open window” and this article explores ways that we can measure and mitigate the risk of immunosuppression in athletes.
Endurance exercise can induce oxidative stress due to an increased production of reactive oxygen species (“ROS”). Oxidative stress can cause skeletal muscle damage, fatigue, pain, delayed onset muscle soreness and impair performance and recovery, caused by an inflammatory reaction to protect against tissue damage. Ultra-endurance events including ultra-marathons and ironman triathlons with very high training loads have been associated with an acute reduction in antioxidant capacity and increased markers of oxidative stress (2), justifying the need for athletes to monitor their training loads and support antioxidant capacity.
During exercise, increases in adrenaline and cortisol are associated with an increase in leukocytes and neutrophils (immune cells that are responsible for defending against viral and bacterial infections), but high-volume training can suppress these cells. Leukocyte and neutrophil count tends to be substantially lower in endurance cyclists and triathletes (3), which could be due to their migration to skeletal muscle damage (1), meaning they are not available to fight off infections.
High levels of stress can lead to immunosuppression, so whilst elite endurance athletes are susceptible to increased risk of infections, recreational endurance athletes can be too because of juggling their training schedule with the demands of family and work. This highlights the importance of supporting athletes to manage their stress loads more effectively. Psychological stress also needs to be considered when preparing for competitions, which can involve long-haul travel (increasing exposure to infectious agents) and poor sleep.
Heart Rate Variability (“HRV”) is a useful non-invasive tool to monitor the nervous system’s response to stress and to regulate training load if required. A high HRV indicates more resilience to stress and greater cardiovascular fitness, whilst a low HRV has been linked to depression and anxiety.
How can nutrition help?
It is important that the athlete’s macronutrient requirements are met. Elevated carbohydrates increase plasma glucose which reduces the release of cortisol, and consequently, reduces stress placed on the immune system. Sport nutrition guidelines suggest that 30-60g carbohydrates should be consumed per hour of exercise. Endurance athletes also require 1.2g to 1.6g of protein per kg of body weight per day.
A diet rich in micronutrients from fresh fruit and vegetables (organic where possible) is important to mitigate oxidative stress and to regulate the inflammatory response. Some micronutrients and their benefits are listed below:
Phytonutrients such as catechins found in cocoa, green tea and grapes have anti-inflammatory action and protect cartilage, whilst quercetin found in apples, green tea and berries has antioxidant properties and can improve lean body mass, basal metabolic rate and total energy expenditure in athletes.
- vitamin A: eye health, immune dysfunction in the gut, reproduction
- vitamin C: collagen production, protein metabolism, adrenal function
- vitamin E: production of smooth muscle cells, regulates gene expression
- copper: immune function, bone and connective tissue health, cardiovascular system
- zinc: cell growth and replication, immunity, carbohydrate metabolism
- selenium: thyroid function,
Vitamin D3 is important for antimicrobial activity and is involved in immune cell regulation.
Iron is necessary for immune cell production, oxygen transport and energy production. Vegan and vegetarian athletes need to combine vitamin C with plant-based iron to increase absorption.
The omega-6 to omega-3 ratio should be monitored to ensure an adequate intake of anti-inflammatory omega-3 fatty acids.
Considering that 70 per cent of the immune system is contained within the gut, with 80 per cent of secretory IgA in the gut-associated lymphoid tissue, probiotics may reduce the risk of URTIs and gastrointestinal illness during stressful periods of training and competition
Glutamine can be deficient in overtrained athletes and significantly reduced following intense training efforts, which can compromise lymphocyte immune cell function.
As well as ensuring that the athlete’s nutritional needs are met, lifestyle support is also important to ensure that the athlete is managing stress levels, training load, personal hygiene and sleep, to provide the body and mind with the tools to cope with the psychological and physiological demands of training and competition. This reduces the risk of URTIs and tissue damage, and promotes optimal performance and recovery for training and competitions.
If you would like to learn more about how nutritional therapy can support your athletic performance, I would love to offer you a complimentary discovery session. It’s a session especially for endurance athletes who wish to sustain their energy levels, experience quicker recovery times and achieve their performance goals faster. During that time together, we will get clear on where you are now with your challenges and what is standing in your way. If you would like to set this up, please click here, and we can arrange a time to speak, thanks!
- Cruz G et al. (2016). Leukocyte Populations are Associated with Heart Rate Variability After a Triathlon. Journal of Human Kinetics. 54:1. pp.55-63.
- Elkington L et al (2015). Inflammation and Immune Function. Antioxidants in Sports Nutrition.
- Horn PL et al. (2010). Lower white blood cell counts in elite athletes training for highly aerobic sports.European journal of applied physiology.110:5. pp. 925-932.
- Moreira A et al.(2009). Does exercise increase the risk of upper respiratory tract infections? British Medical Bulletin. pp. 111-131.