When I was ill a couple of weeks ago I thought it would be apt to write about the common cold and other illnesses, and how athletes can either reduce the risk or minimise the severity of infections through nutritional practices.
There is a lot of research on this area with regard to athletes. Although there is no consensus on many nutritional practices, I thought it would be interesting to discuss several as you may find one that helps.
Athletes and infections
It has been suggested that athletes undertaking prolonged intense exercise may be more susceptible to infections due to the effect of this intense exercise on suppressing the immune system. Dr. David Nieman produced the J-shaped curve (on the right) which suggests that, while moderate forms of exercise can be protective against infection, excessive amounts that stress our system may increase the risk of infection.
Therefore, for those who may already be susceptible, it is important that the correct nutrition is in place in order to try and reduce this risk. After all, illness means no training and no training can lead to poorer performance!
Nutrition and infections
Specific nutrients play a vital role in the immune system. The macronutrients (protein, carbohydrate and fat) are involved in immune cell metabolism and the building of the immune cells, and many micronutrients are antioxidants that fight against stress to the system.
There are continued debates about what nutritional practices may help fight infection, some of which are discussed below.
Vitamins and mineral supplements
Vitamin C has long been considered a cure to the common cold, mainly due to its role as an antioxidant, but is this really the case for athletes? There is indeed some evidence for a role in vitamin C reducing the incidence of infection, but it is not all compelling. This may be due to the fact that athletes naturally regulate up their antioxidant defences and so supplementation would have no further impact. Perhaps one to try as it is not particularly expensive, but don’t go overboard as excessive supplementation may lead to abdominal pain and nausea.
There is not much consistent evidence to show that other vitamin supplements have a positive effect on reducing infection risk. If you are going to supplement with any vitamins, be aware that mega doses can have toxic effects and may even impair your immune function. Athletes tend to have a higher food intake and so they should reach above average levels of vitamins if they eat a healthy and balanced diet.
This mineral is essential to the development of the immune system. There are equivocal findings relating to the effect of zinc on infection severity, however, what is clear is that if they are taken to treat the common cold, they should be taken within 24 hours of the onset of symptoms. As with vitamins, mineral intake in athletes tends to be above average and supplementation may not be needed apart from special circumstances (e.g. reduced food intake due to travelling).
Glutamine plays a pivotal role as a fuel for immune cells and so it is plausible that supplementation may help boost the immune system, however, the majority of studies do not show a positive effect of supplementation on reducing the incidence of infections (despite increasing plasma levels). Perhaps this is due to plasma levels not being sufficiently depleted to have a detrimental effect on immune cells. Therefore, supplementation for immune support is not recommended.
Echinacea and other herbal products
There are some positive findings for the effects of certain herbal supplements, such as Echinacea, on the immune system, however, more research is needed before recommendations can be made.
These are associated with reduction in incidence and duration of infection but mechanisms and details of dose and timing of supplementation are not clear. Perhaps one to try, however, the daily use of probiotics could be expensive in the long term.
Not only is this a fuel for immune cells, but when stores are depleted the level of cortisol (stress hormone) in our blood increase, which has a negative impact on many immune parameters. Both supplementation of carbohydrate during exercise, as well as adequate dietary carbohydrate intake, help attenuate the suppression of the immune system. However, whether this results in a lower incidence of infection is not so clear, perhaps because of many other factors are at play.
High fat diets negatively impact on the immune system, which is suggested to be the result of reduced micronutrient intake. On the flip side, low fat diets also put more stress on the system and can enhance the risk of infection. So make sure you stick to a balanced diet including at least 20% of your total energy intake coming from fat.
Similarly, protein is a nutrient that is key in building immune cells, and so should not be forgotten. Remember, you need around 1 g protein per kg of body weight each day – so if you weigh 70 kg you need approx.70g protein – however, this value can increase up to 1.5 g per kg body weight for those who undertake intense exercise training.
Most rugby players tend to eat more than the average person, however, they also tend to go through phases of fat loss in which their energy intake may be reduced. It is important to ensure you still eat enough to support your immune function (amongst many other bodily functions!) as a restricted energy intake can increase susceptibility to infection.
Dehydration can enhance the stress response in a similar way to carbohydrate. On top of this, we have some important immune cells in our saliva which can be reduced when dehydrated – this can heighten the risk of infection. So make sure you always have a water bottle to hand!
Polyphenols and flavonoids – Watch this space
Polyphenols and flavonoids (fruit and vegetable extracts) seem to be the hot topic at the moment. Supplementation with these has proven to be successful in reducing the risk of infection and research seems very promising, although more research is needed to determine more specific things such as dose and timing of intake. One example is “quercetin”, which can be found in apples, citrus fruits, onions, parsley, red wine and tea. However, most of the studies that showed an effect used supplements, so “quercetin” from foods may not be sufficient and supplementation may be necessary.
As we can see, there are possible advantages to many different supplements. One idea is that in the future a mixture of different supplements in one could be used as this will likely lead to a positive response to at least one of the active ingredients. But as always, the key is balance – make sure you have enough energy, protein, carbohydrate and good fats, stay hydrated and eat plenty of fruit and vegetables to get the most protection from your diet.
Don’t forget, as important as nutrition is, other factors play a role in susceptibility to infection – so make sure you limit the level of stress in your life and get adequate sleep too, oh and don’t forget to wash your hands!