I believe there are 4 main areas that sport nutritionists can help athletes. 

 

 

I would say that the first 3 are relatively simple to help with and the answers can be found in most half-decent sport nutrition text books. However, supporting the immune system is not as simple with good research on this topic not as easy to come by. Most studies have to rely upon observations, i.e. give a particular diet or supplement and assess how many people may or may not get ill. Although not ideal, this research has led to several suggestions that may help to reduce the number of training days lost to illness.

 

Whilst moderate exercise is good for our immune system, there is evidence to suggest that high intensity and prolonged training actually increases our risk of infection. This is especially the case in the hours after exercise, a period often referred to as a ‘window of opportunity’. In the UK the average adult will suffer from 2-4 colds per with the symptoms usually clearing within 2 weeks. This means that over the course of a lifetime we spend approximately 2.5 years battling the symptoms of a cold! In simple terms, a cold is a mild viral infection of the nose, throat, sinuses and upper airways. The current advice is to rest, drink plenty of fluids and let the symptoms go away. But is there anything nutritionally we can do to reduce our chances of getting a cold or improve recovery time should we be unfortunate enough to get one?

The biggest nutritional factor associated with immuno-depression is inadequate total energy intake, for example when someone is trying to reduce body fat. This can be compounded if people are trying to lose weight through following a low carbohydrate diet. There is a strong association between plasma glucose, the stress hormone cortisol and compromised immune system. Therefore, one piece of advice to help boost the immune system is to consume carbohydrates during prolonged exercise, especially if this is high-intensity exercise. Research suggests 30-60g of carbohydrate per hour should be enough. 

 

There is also evidence that protein deficiencies could affect T cells increasing the chance of opportunistic infections and so it is also crucial that sufficient protein is consumed (about 1.2-1.8g per kg body mass) on a daily basis. Although many athletes easily achieve this target, there are a growing number of athletes following a vegan lifestyle and particular attention should be given to ensure these athletes are not immune compromised due to low protein intakes.

 

During exercise, it is not uncommon to become dehydrated and this again can be a problem for the immune system. Dehydration not only increases the production of stress hormones but also decreases salivary flow rate reducing salivary IgA (one of the first defences against a pathogen). It is therefore crucial that athletes do not get a dry mouth during exercise and are therefore encouraged to drink fluids regularly during training and competition, even if it is a cold day.

Although there are not many micronutrients that can be supplemented to prevent coughs and colds, there is evidence that micronutrient deficiencies can compromise immune function. I therefore make sure that athletes are always consuming a diet rich in vitamin and minerals, especially during the winter months and if there is any concern we do sometimes consider supplementing.

 

In recent years there has been growing interest in the so-called immune boosting supplements. Research in this area is growing and it is certainly hard to give definitive advice at the moment. The hot supplement at the moment in this area is Zinc Acetate Lozenges with data suggesting that zinc lozenges can reduce a colds’ duration by approximately 44% (401 days of less symptoms over a lifetime). It must be stressed however that the dose has to be >75mg per day for a short period of time (< 7 days). This is a very high dose and needs specialist advice to avoid the risk of toxicity.

 

Other supplements suggested to boost the immune system include 400mg of vitamin C (modest evidence), glutamine (weak evidence), beta carotene (weak evidence), Quercetin (modest evidence), curcumin (emerging evidence) and Manuka honey (no evidence). Perhaps the best of this bunch is vitamin C which may reduce the length of time and severity of a cold but does not seem to prevent it.

In summary, it is almost inevitable that at some time in our life we are going to get run down and feel ill. I guess my top tips to reduce our chances and to speed up recovery would be

 

1. Pay close attention to hand hygiene especially in the winter months. Many illnesses are spread from hand to mouth contact so try to reduce this. And do not neglect soap and water - sometimes this is better than alcohol hand gels.
2. Avoid nutritional deficiencies and remember if you are trying to lose body fat there is a chance your immune system will be somewhat compromised. 
3. Avoid getting a dry mouth during exercise. Drink regularly and if this is prolonged consider adding 30-60 g per hour of carbohydrate.
4. If you do feel a cold coming on, consider Zinc Acetate Lozenges but get some qualified advice on this first. Also 400mg of vitamin C may help speed up the recovery if taken daily during this period.
5. The evidence for the other immune boosting supplements is so far weak. It is perhaps better to spend your money on the more tried and tested strategies suggested above and improving overall diet quality.
6. Like all my advice, if you are going to supplement please use ones on the “Informed Sport” register and do this after seeking qualified advice, ideally from someone on the SENr register.