If you’re striving for a new PB then avoiding the lurgy could be your biggest training asset. Andrew Hamilton looks at what the very latest research says about nutrition and immunity.


In a carefully-crafted training programme where you’re looking for incremental gains in performance, taking a month or even a week out due to illness can be a huge setback. The most common type of infections in sportsmen and women are upper respiratory tract infections (URTIs – coughs, colds, sore throats). Depending on the severity of an URTI, your training might be compromised for anything from a couple of days to a couple of weeks.

If you’re lucky, you’ll be able to do some gentle training during an URTI, but you may find it impossible to train at all. Equally however, an infection can be more serious. A bout of influenza or a chest infection can easily result in a month or more of lost training time, which can have disastrous consequences for your fitness thanks to the process of detraining, where gains in fitness are steadily lost once training is ceased.

Given these facts, it’s natural to ask whether there are any proven ways of supporting immunity – particularly during the winter months when coughs, colds and other URTIs abound. Assuming you’re already doing the essentials (see page 85), let’s look at what some of the recent research says about immune-enhancing nutrients.

Vitamin D vitaman d

In recent years, the evidence has been mounting that 1) the maintenance of normal human immunity is highly dependent on the vitamin D status of individuals, and 2) that many people (including athletes) have sub-optimum levels of vitamin D. Until very recently, there were no specific studies on athletes, vitamin D and immunity but a large study published a couple of years ago makes fascinating reading.

The goal of the study was to determine the influence of the athletes’ (ranging from recreationally active weekend warriors to Olympic triathletes) vitamin D status on their immune function and the incidence, severity and duration of URTIs over the course of a 4-month winter training period.

In a nutshell, compared with low-vitamin D status athletes, athletes with high levels of blood vitamin D had fewer episodes of URTI, less severe symptoms when they did occur and greatly improved levels of immune markers (see graph).

Not only was this study the first to show that optimum vitamin D status in athletes undergoing vigorous training can boost immunity, it also used a large number of subjects from a range of sports, which means its findings are likely to be valid and widely applicable.

In another recent study on vitamin D and athletes, researchers found that vitamin D3 inadequacy/deficiency was commonplace; some 62% of the athletes and 73% of the non-athlete controls had blood vitamin D3 levels of less than 50nmol per litre – i.e. sub-optimum, deficient or severely deficient.

These results fit with other studies showing that many athletes have less than optimum levels of vitamin D in the body, with negative implications for immunity. Low vitamin D levels are particularly commonplace during the mid-late winter period, when the body’s reserves of “sunshine manufactured” vitamin D during the summer months start to run low.


Probiotics (for example, found in some yoghurt/ yoghurt drinks) are defined as “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host”.

During the last fifteen years, there’s been an explosion of research into the immune-boosting properties of probiotics and the results have been very encouraging. What’s been lacking until more recently however are good placebo-controlled randomised trials carried out in the field – that’s to say on athletes engaged in their normal training programmes.

To complicate matters further, numerous strains of probiotic bacteria have been used in studies, some of which may be far less effective than others. This all makes it difficult to determine just how effective probiotic supplementation for someone in hard training really is.

A recent study looked at the effects of probiotic supplementation on the duration, incidence and severity of infections in 30 elite rugby union players who took a supplement for 4 weeks. During the probiotic treatment 14 of 30 participants never experienced a single URTI or gastrointestinal episode, compared to 6 of 30 on the placebo supplementation (a scientifically significant reduction).

Also, the number of days of illness tended to be less when the probiotic was taken.

Another study looked at Lactobacillus fermentum supplementation and gastrointestinal and respiratory-tract illness symptoms in 99 competitive cyclists. The cyclists were randomised into either a probiotic or placebo treatment group for 11 weeks in a double-blind, randomised, controlled trial – the most rigorous kind of scientific trial.

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At higher training loads, there was an average 70% reduction in the severity of gastrointestinal illness, which became more pronounced as training load increased. Also, the duration and severity of URTI symptoms reduced by around 30%.

In another double-blind, placebo-controlled cross over trial, scientists investigated the use of Lactobacillus fermentum in 20 elite male runners over 4 months of winter training.

Athletes taking the probiotic supplement reported less than half the number of days of respiratory symptoms during the supplementation period (30 days) compared with the placebo group (72 days). Reported illness severity was also lower for episodes occurring during the supplementation period.

In a further recent study, 84 athletes took either a placebo or probiotic supplement (Lactobacillus casei shirota) for 4 months. The athletes taking the probiotic experienced significantly less URTIs than those who didn’t.

However, to illustrate that all not all probiotics are created equal, the same scientists investigated another probiotic (Lactobacillus salivarius) on infection, cold symptom duration and severity, and immunity in 66 endurance athletes and found that it didn’t reduce the frequency of URTIs.

In other words, it seems that if you’re tempted to use probiotics, you should try a strain for which there is good evidence in the scientific literature.


Cystine and theanine are two amino acids that are involved in the synthesis of a compound called glutathione in the body. Glutathione helps maintain the optimum activity of very important immune cells called “natural killer” (NK) cells, and recent research suggests that supplementation of these nutrients could be advantageous for immune functioning in athletes.

For example, in one study, cystine (700mg) and theanine (280mg) were given once daily for 2 weeks to 15 men who undertook a week of normal training followed by a second week where their training load was doubled. In the high-intensity week, NK cell activity declined when the men took a placebo.

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However, when they took cystine/theanine, NK activity was restored. In another study, 15 long-distance runners were each allocated to a cystine/theanine group and supplemented for 10 days prior to the start of an intense training period.

There was also a placebo group. Compared to the placebo, the cystine/theanine supplement prevented a decrease in the immune function, and reduced the incidence of infection associated with the drop in immunity commonly observed after continuous intense exercise.

These results tie in neatly with the results from a 2010 study, which investigated the effects of cystine/theanine supplementation on the common cold (the most common URTI) in human volunteers. A total of 176 healthy male volunteers received either placebo or cystine/theanine (490mg) tablets twice daily for 35 days.

The researchers then measured the incidence of common cold symptoms using standardised and rigorously validated questionnaires. The results showed that the incidence of common cold symptoms during the trial was significantly lower in the cystine/theanine-supplemented group than in the placebo group.


Beta glucans are naturally occurring compounds (for example, found in the bran of cereal grains, and some mushrooms) that can exert positive effects on the function of important immune cells. However, while there’s good evidence for the immune benefits of beta glucans in the general population, research among athletes undergoing heavy training is more limited.

One double blind, placebo-controlled study investigated the effect of pleuran (an insoluble glucan from a mushroom known as Pleurotus ostreatus) on immune responses and incidence of URTIs in 50 athletes over a 3-month period.

The results showed that the pleuran significantly reduced the incidence of URTI symptoms and increased the number of circulating NK cells. Since NK cells are key immune cells whose job it is to fight off viral infection, the scientists concluded that: “pleuran may serve as an effective nutritional supplement for athletes under heavy physical training.”

Another study looked at whether beta-glucan supplements from Pleurotus ostreatus were able to combat the temporary immune dip that invariably occurs following a bout of highintensity exercise.

Twenty elite athletes took either beta-glucan or placebo supplements once a day for two months; the placebo group typically showed a 28 percent reduction in NK cell number activity during the recovery period, whereas no such reduction was found in the beta-glucan group indicating superior immunity during the all-important recovery period.

Summary and Practical Recommendations

Keeping your immunity in tip-top condition requires a multi-faceted approach, which means attending to lifestyle factors (getting enough good sleep, managing stress, eating a high-quality diet and so on) and ensuring you allow sufficient recovery in your training programme, especially when the intensity increases.

However, recent science suggests that certain nutrients may confer additional immune protection and these may be useful, particularly over the winter months or during periods of high workloads.

Practical Implications

  • Ensure your day-to-day diet contains plenty of vitamin D and is high in carbohydrate. Training while consuming insufficient carbohydrate is stressful for your body and can impair immune function.
  • Consider using carbohydrate drinks during and carbohydrate/protein recovery drinks immediately after training to minimise the post-exercise dip surge in stress hormones (which suppresses immunity).
  • If you suffer from frequent winter URTIs, consider taking a daily vitamin D supplement of 1000-2000IUs throughout the winter months.
  • Probiotics can help support immunity but stick to those strains proven in scientific studies – e.g. Lactobacillus fermentum.
  • If you’re particularly vulnerable to URTIs, you can consider trying cysteine/theanine and/or beta glucan supplements.
  • Don’t forget good hand hygiene, which can significantly reduce your exposure to the viruses responsible for URTIs.