Why are you ill, your so fit? Have you heard this? Have you been struck down with a chest infection shortly after a big race. Well if you have I’m not surprised. The immune system takes a big hit with the volume of training many endurance athletes go through.

First a quick overview of the immune system.

We are born with a fully functional immune system, our innate immune system. We also get another line of defence with our acquired immune system. As the name suggests this one is built up over our lifetime, and adapts to previous infections. As well as this we have antibacterial saliva, tears and stomach acid. Mucus to trap nasties and good gut bacteria who will out-perform bad bacteria if you look after them.

Our innate immune system is made up of killer cells.

Our acquired immune system is made up of killer cells, helper cells and regulatory cells.

Now exercise can dampen the effect of helper cells. This is bad as the helper cells will decide how the immune system responds to threats. This basically means some athletes during prolonged heavy training will have no anti-viral response. This is why colds are caught during training. The window that you are susceptible to viruses has been shown to be 1-9 hours after training depending on factors such as type of session, intensity etc (Nieman et al., 1995).

During exercise all immune cells are released as the body thinks it is under attack due to the stress incurred. However, after exercise stops, all immune cells are decreased (apart from some killer cells which are released from bone marrow due to the effect of cortisol). So athletes will have a lower than average concentration of immune cells in the blood.

Endurance trained athletes had the highest resting blood levels of IL-10. Now IL-10 is a very important messenger released by helper cells to switch off the immune system.

So what can I do?

Nutrient deficiencies also lead to immune breakdown, and supplementing can help build it back up. Lack of vitamin A, Iron, zinc, copper and selenium are all causes of immune malfunction. Vitamins C, D and E are also important for our immune system. There is a high prevalence of vitamin D deficiency in athletes, vitamin D guards against stress fractures, infectious disease, impaired muscle function and inflammation. Supplementation is never as good as getting sunlight but will help during winter months. Vitamin E has been shown to reduce inflammatory signallers which in turn reduces need for the anti-inflammatory IL-10 (Fischer et al., 2004). 600mg of vitamin C taken after an ultramarathon, lowered the incidence of infections (Peters et al., 1993).

One of the biggest causes for immune breakdown is Protein-energy undernutrition, in short make sure you are eating enough to fuel your training. And if you are eating a lot of healthy nutritious foods, you will be getting more vitamins and minerals into your body. Carbohydrate when consumed during exercise reduces IL-10 levels (Gleeson et al., 2004).

If you are training hard your immune system will be compromised, there is no getting away from that. If you are then not eating enough or getting enough vitamins and minerals in your diet, you will only make a bad situation worse.

One more interesting study, German researchers found that consumption of non-alcoholic beer of 1-1.5 L a day for 3 week before and 2 week after marathon competition reduces postrace inflammation and infections of the upper respiratory tract, theorised to be due to polyphenolic compounds found in beer (Scherr et al., 2012).

So get those (non-alcoholic) beers in.


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