Improving athlete immune function and support

I generally consider myself to be pretty hardy and robust, rarely suffering from illness. However, when I was selected to compete at the 2007 World Championships, I came down with a really bad cold in the pre-competition holding camp, which affected my training for about a week. In 2009, the week of the European Indoor Championships, I again had a terrible cold. In 2005 and 2011, I also was hit with really bad colds in the days before running my seasons best times. Maybe I just remember those colds because they’re linked to an important event I was taking part in, but an increasing body of research shows I was not alone and that athletes become increasingly susceptible to illnesses in the run up to major competitions.

» Learn more: This article is part 4 in Craig Pickering’s Performance Health Series. Part 1 discussed the concept of performance health, part 2 reviewed leading injury models, and part 3 explains load and load measurement.

Looking at the extent and causes of illness

I mentioned this in the introduction to this series: in a study of Australian athletes three months before the Rio Olympics, 100% (!) of them reported at least one episode of illness in the preceding month. Similarly, in the Raysmith and Drew paper that has been so influential to my stance on this topic, most illnesses suffered by athletes occurred within two months of their target event. Finally, research at the Olympic Games suggests that around 5-10% of athletes suffer an illness during the period of the Games, again likely hampering performance. It strikes me as unacceptable that we should spend all this time developing athletes to their potential, only to have performance at a major championship put at risk due to an illness. We must do better.

Just like sports injuries, the development of illness within sportspeople is complex and multifactorial. In the study of Australian Olympians, low energy availability and increased self-reported anxiety were associated with an increased risk of illness, with similar results being reported in other studies. These relationships also have a feedback loop, with alterations in illness risk also affecting injury risk; during the 2015 World Athletics Championships, for example, athletes with an illness that increased their anxiety were five times more likely to suffer an injury during those championships. As you might expect, training load also influences illness rates, with illnesses more likely during periods of rapid training accumulation. Life load is also a big factor, such as the stress associated with academic exams.

The relationship between exercise and immune function

When it comes to research on exercise and immunity, perhaps the most well-renowned researcher in this area is Professor Neil Walsh, currently at Liverpool John Moores University. In a highly influential 2011 Consensus Statement on immune function and exercise, Walsh and his co-authors explore the state of the research on exercise and immune function. A model to help our thinking here is the “inverted-U” relationship (or a J-shaped curve) of exercise and immunity, whereby high and low levels of exercise—both acutely and chronically—appear to decrease immune function and increase the risk of illness, with moderate levels of exercise enhancing it. As a result, athletes tend to have good immune function, but during periods of high accumulated training loads, increased competition stress, and/or one-off high doses of exercise (e.g. a marathon), their immune function appears to be somewhat suppressed, opening the window for illness to occur.

Supporting immune function

So what can we do to support the immune function of our athletes, and limit the risk of illnesses in close proximity to major championships? In 2019, a group of authors laid out the evidence for how to best keep athletes healthy in the run-up to the 2020 (as it was then) Olympic Games; the lessons contained within make useful reading for us all. They recommended the influenza vaccine, primarily for Southern Hemisphere athletes in the 6 months prior to the Olympics, but it is likely useful for all athletes during their winter as a way of reducing the chances of lost training time. They also recommended:

  1. Optimizing hygiene practices: minimize risk of infections by regular hand washing for ~20 seconds, regular cleaning of sporting equipment, minimizing shaking hands, avoiding sick people, and, where possible, crowded areas and young children.
  2. Maintaining carbohydrate availability: Reduce the risk of low-energy availability by matching carbohydrate intake with training demands.
  3. Probiotic supplementation: Probiotics are believed to help reduce the incidence, severity and duration of upper respiratory tract infections, and so may be useful for use 2-3 weeks prior to the major competitive event.
  4. Minimize stress and anxiety: Both are risk factors for illness (and injury), and are likely to be heightened close to competitions, especially important ones. The groundwork for this is laid during the preparation period, where athlete resilience and psychological skills can be enhanced and developed. Close to competition, the utilization of relaxation skills (such as mindfulness) comes to the fore, as does the monitoring of athlete stress and wellbeing through questionnaires such as REST-Q.
  5. Improve sleep: Sleep deprivation is a significant risk factor for illness (and injury and underperformance), and so good sleep hygiene should be support and reinforced. Athletes should aim for ~8 hours sleep per night, and avoid stimulating activities and blue light before sleep.

In addition, for athletes undertaking training and/or competitions in their winters, when their exposure to UV light is likely to be low, the authors recommend monitoring vitamin D levels within the athlete, and supplementing with vitamin D as and where appropriate. Vitamin D has been shown to support immune function, and so is therefore likely an important consideration when it comes to staying free from illness. Where vitamin D blood testing is not available or practical, supplementation of 1000 IU of vitamin D3 per day is potentially a safe, pragmatic response.

Research also suggests that female athletes appear to be somewhat more susceptible to illnesses during the competition period; at the 2016 Olympics, for example, female athletes were about 40% more likely than their male counterparts to suffer an illness, a trend which holds true for general training, with women also suffering from upper respiratory tract infections for longer than males. Again, this highlights the complex and multifactorial nature of injury, and, in this case, illness. Female athletes are at an increased risk of experiencing low energy availability, and this has been specifically shown to increase the risk of illness in this population. Ensuring optimal energy intake in all athletes, but especially females, is therefore crucial in optimizing performance health and reducing the change of illness and injury at the most inopportune times.

Further recommendations

Of course, illness is not just a threat during the competition season. In the second part of their Consensus Statement on exercise and immunity, Walsh and colleagues provide some guidelines for maintaining the immune health of athletes during training periods, including:

  1. Rapid daily and weekly increases in training loads should be minimized.
  2. Ensure adequate intakes of energy, carbohydrate and protein.
  3. Avoid micronutrient deficiencies.

The effects of psychological stress also need to be accounted for, which Walsh also addressed in a 2018 paper on psychological stress in the athlete and immune health. Key steps to take include:

  1. Understanding that life stress is an important aspect of load, and should be considered in athlete monitoring.
  2. Using stress management techniques, such as mindfulness meditation, where necessary to assist in the control of stress and anxiety.
  3. Monitoring of life demands (using the DALDA) questionnaire, or mood (POMS), stress (Perceived Stress Scale) and anxiety (State-Trait Anxiety Inventory) where required and feasible.

A final area discussed already, but that we can all take a further look at is nutrition. The influence of nutrition on immune function, and its relationship with the risk of illness, was also a key theme look at by Professor Walsh in an updated open-access article on the topic late last year. This topic is one I look tackle in more depth in the next article in this series, where I explore the relationship between energy availability, illness, and injury.