A couple of weeks ago I read a journal article, and it challenged me and my way of thinking, so I thought: what a great discussion this would be! Since the early 1980s, scientists have been investigating the immune system of athletes. The central theory of this research was that heavy exercise reduced the athlete’s immune system and provided a somewhat ‘open window’ for infections to occur after heavy exercise. There is actually a lot of research that has looked at heavy training loads and accumulative exercise stress and whether it increases the risk of infection in athletes – though for some time the ‘open window’ theory has been in doubt. 

What are we really seeing?

Let me put it this way: a marathon or a long-distance triathlon (half and full ironman distance) puts huge amounts of exercise stress on the body in a single hit. Now, according to the ‘open window’ theory nearly everyone would get sick after completing a marathon. Imagine that; run 1 marathon and then suddenly majority of the runners get sick. Please correct me if I am wrong, but while a small handful of people may get sick after a marathon, the large majority can carry on with life as normal and feel fine. Some researchers looked into this phenomenon at the Stockholm Marathon in 2000 and they found no increase in infections or colds after the marathon2. What they did find is that pre-race symptoms were the best predictors of infection after the race. Aside from exercise, there is plenty of research in military personnel through to the everyday person that has shown that winter, high levels of psychological stress including anxiety and depression, and short duration of sleep are more likely to cause illness than running a marathon. Stress and poor sleep have what we call a dose-response relationship, where the more stressed or the less sleep you get, the more likely it is that you will get sick. It is quite probable that if you are feeling increasingly stressed at work, or maybe even feeling that increase in stress and anxiety leading into a race that you may be putting yourself at risk of getting sick before the event. Guess the key point here is make sure that you can get enough good sleep (quality and quantity > 6 hours) and find ways to reduce your stress, lift the mood and reduce anxiety especially leading into race day.

Now what about all these nutritional supplements that we can take to boost our immunity?

Nutrition is something that we can use to support our immune health. A healthy immune system is one that can clear bacteria and viruses and to do this it needs to get enough energy from the food that we eat. Not only does a healthy immune system require enough energy to perform, but it also requires enough protein (amino acids) for cell growth and DNA synthesis. Getting in enough protein when you are sick is required to help produce all the rapid responding cytokines and acute phase proteins that help the body respond to the invading virus or bacteria. Now we shouldn’t forget our micronutrients, with iron, zinc and magnesium all used to support DNA synthesis in our immune cells and vitamin C and E helping our antioxidant defence. This is especially important during infection when there is high oxidative stress. It’s also important to note that vitamin C and E can help limit tissue damage. Other nutritional supplements that tend to be supported by research is probiotics (to support gut microbiota, especially post infection where antibiotics has been taken), and zinc lozenges that can help reduce infections in the throat. 

Immunology has focused on understanding all the weaponry (components) of the immune system that will fight the infection, this is usually referred to as immune resistance. But here is where it got interesting for me, an alternative idea was proposed, one that considered not only our ability to fight the infection but our tolerance and ability to endure invading bacteria.

How the immune system really works…

Let’s consider a castle for a moment: there are people that will live in the castle and each will have different roles like providing food or repairing broken components (walls, roof, floors). Now imagine an army comes to attack the castle, the occupants inside the castle must decide what type of attack they will use against the new threat and what weapons will help them execute the best attack. The occupants of the castle know that a battle will be costly and will diminish the occupant’s numbers and their resources. So, choosing the right plan of attack is key, and basically this is exactly what your immune system does: it chooses its battle wisely. If we then think about this as our immune system response, it would mean that our immune system must execute a controlled and appropriate immune response whenever it comes in contact with foreign bacteria or a virus. A boisterous immune system will probably cause tissue damage and re-direction of energy away from vital processes, whereas a feeble immune response will increase your risk of infection. Since a full-blown immune response will produce tissue damage and will require a huge amount of energy, something the human body is not overly supporting of, perhaps the human body has adapted to control and tolerate non-threating bacteria.

A good example of this would be the fact that we have countless bacteria in our gut that support our digestion of food, but our immune system is not running a full-on attack on our gut every moment of the day. Attacking the gut bacteria probably doesn’t happen because our body’s immune system actually appears to have evolved to balance resistance and tolerance that allows us to fight infections when there is an appropriate need to, but also allows us to have a mutually beneficial relationship with some bacteria, like those which we find in our gut.

So, here is the premise of this blog…

Maybe this new perspective of achieving a good balance between resistance and tolerance may help understand our health (as an everyday busy person or athlete) and which nutritional supplements may be able to help us. Now quite a lot of research using supplements in exercise and athlete immune health has looked at ways to reduce that ‘open window’ period of a suppressed immune system after exercise.  And well like the open-window theory that we have been chasing, the research in supplements targeting immune weaponary (resistance) has shown minimal benefits. One exception to this though would be the use of zinc to reduce throat infections durations especially if you take it as soon as you present with any cold symptoms (can reduce cold duration by up to 3 days!). So, stock up on that zinc before winter and cold season.

Let’s consider this, maybe we should look at using supplements to support our tolerance of an infection. In this way could we use our nutritional supplements at specific times to reduce the severity and duration of our sickness. Using this approach a few supplements start to stand out.

  1. Probiotics: are basically tablets with live microorganisms that can support your gut bacteria and immunity. Probiotics can support the absorption of nutrients when you are sick and the products of these microorganisms’ metabolism (lactic acid) may also prevent unwanted bacterial growth. Probiotics can also provide an anti-inflammatory effect that could help prevent unwanted inflammation to foreign yet harmless substances in the gut, which is great for your gut and overall health. For the athletes out there, daily supplementation for 28 days through 4 months has been shown to reduce cold severity and symptoms and less frequency of colds compared to athletes who didn’t take probiotics… Have I convinced you to get some yet? 1,3
  2. Vitamin C: now I am sure that most people would be reaching for this vitamin come cold season. Vitamin C is a brilliant scavenger of reactive oxygen species in the body, and so there is actually quite good scientific data to support the use of vitamin C to improve your tolerance to oxidative stress and protect your tissues from damage during infection. Now some research in marathoners, skiers or soldiers showed a decrease in the number of colds by up to 52% by taking a daily supplement of vitamin C (0.25-1.0g/day). Some recent debate has discussed whether or not taking a high dose of vitamin C before training will stop our bodies from adapting to the exercise stress (which we use to improve our fitness), but this may require super high doses and not the amount we can get from our daily vitamin C supplement that you buy at the supermarket. So I guess the best plan may be to take some vitamin C and maybe aim to take it in the morning before you complete any exercise. 5
  3. Going into winter, we have shorter days, longer nights, and basically our bodies crave sunlight. Why? Well because it is how we make a vital vitamin: Vitamin D. There is so much research showing how vitamin D is essential for our bones, but there are also vitamin D receptors on our immune cells too. When we have enough vitamin D in our body, it will support our immune cells and their anti-inflammatory effect. The evidence to support avoiding vitamin D deficiency in athletes in order to prevent the occurrence of colds and maintain our immune system is really strong. With this one, I would suggest getting a blood test done before you reach for the supplement bottle though, and if possible, make sure for at least 10-20 min a day you let the sun onto your skin- this will help you make enough vitamin D without the need of supplements! 4

And there you have it! Hopefully I have challenged you, as I was, to not only think about supporting your immune system’s ability to fight the infection but also to think about how we can support our immune system’s tolerance6 (the ability to dampen your immune response and control the infection to a non-damaging level to your body) – especially as we start heading into the cooler months and we all want to reduce the severity, frequency and duration of any colds or flus that we could get. Because let’s be honest: being sick is never ideal.

Dr Claire Badenhorst

Every clinic needs a doctor, at Sports Lab, Claire is ours. Dr Claire Badenhorst  is our physiologist (PhD Exercise Physiology, Academic at Massey University in Auckland) with research focus areas currently in female health, iron deficiency and endurance athletes. 



Some references:

1.            Cox AJ, Pyne DB, Saunders PU, Fricker PA. Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes. Br J Sports Med. 2010;44(4):222-226. doi:10.1136/bjsm.2007.044628.

2.            Ekblom B, Ekblom Ö, Malm C. Infectious episodes before and after a marathon race. Scand J Med Sci Sport. 2006;16(4):287-293. doi:10.1111/j.1600-0838.2005.00490.x.

3.            Gleeson M, Bishop NC, Oliveira M, Tauler P. Daily probiotic’s (Lactobacillus casei Shirota) reduction of infection incidence in athletes. Int J Sport Nutr Exerc Metab. 2011;21(1):55-64. doi:10.1123/ijsnem.21.1.55.

4.            He CS, Handzlik M, Fraser WD, et al. Influence of vitamin D status on respiratory infection incidence and immune function during 4 months of winter training in endurance sport Athletes. Exerc Immunol Rev. 2013;19:86-101.

5.            Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;2013(1):CD000980. doi:10.1002/14651858.CD000980.pub4.

6.            Walsh NP. Nutrition and Athlete Immune Health: New Perspectives on an Old Paradigm. Sport Med. 2019;49:153-168. doi:10.1007/s40279-019-01160-3.