Optimising immune function in athletes can help in numerous ways. By reducing the frequency and duration of illnesses, it allows more time for training while at peak function. It can also mean that fewer competitions, events, or games are impacted by illness too. While we cannot prevent getting sick 100% of the time, there are certain things we can do with nutrition to help still.
Why This Matters
Getting sick not only leads to missed training sessions or games/events, but it also exerts a lingering negative impact on performance for quite some time after the occurrence. Training intensity is typically reduced for a period of time after returning from the illness.
Minimising the frequency and duration of illness can help improve progress over the long term.
In addition to this, it is athletes can be more likely to get sick during high training phases. This is even more so if it is an intentional overtraining phase.
This theory has been challenged. But there is also not really strong evidence against the idea either.
At a minimum, if illness rates are unaffected by high training loads, minimising the frequency/duration of illness is still a good thing. But if these rates ARE affected by high training loads, this topic becomes even more important.
Probiotics
Probiotic supplementation is an underrated way to improve your immune function.
A large portion (~70%) of the immune system is located in the gut. Intense, prolonged exercise, particularly in the heat, can increase gut permeability. This could make it easier for pathogens to pass through.
Specific probiotic strains can improve gut-barrier function, reducing this issue.
In terms of research, there are around 22 relevant studies on this topic.
Of these studies, 14 reported a significant improvement, whereas 8 showed no noticeable difference.
One study involving participants training ~6hrs per week (so not elite athletes) found a 27% reduction in URTIs over 150 days.
Using a more relevant study on the topic, endurance athletes with high training loads were found to miss half as many training days due to URTIs over the course of 16 weeks. L. fermentum was the supplement used in this one.
More information, including dosages, can be found in our comprehensive blog post on the topic.
It is highly likely that probiotic supplementation, particularly during high-risk phases (travel, intense training or winter, for example) could reduce the likelihood of illness as well as the duration and severity.
Vitamin C
The clear consensus based on the research is that vitamin C can reduce the duration and severity of the common cold a bit.
Meta-analysis data has found reductions in the duration of symptoms of around 8% on average.
One thing that was not found in this data was a reduction in the incidence of getting sick on average.
In the research specifically on athletes within that meta-analysis (rather than the general population), there was a reduction of about 50% in the frequency of upper respiratory tract infections. This research used dosages of 0.25-1g/day.
So even based on general data, there is potential that vitamin C supplementation can help. Although we do not have much research on this, there are some other interesting ideas that can make this more effective:
- Increasing the dosage.
- Supplementing multiple times per day.
Dosage:
With the dosage, some studies use quite low dosages. Increasing higher could help. The main limiting factor for how much vitamin C we can consume orally is that people often get GI symptoms when the dosage gets quite high (e.g. >2g in a single sitting).
Absorption also hits a point of diminishing returns with higher dosages. For example, if you have 2g of vitamin C, you absorb more TOTAL amount of vitamin C, but it is only a small amount more than if you just had 1g.
Timing
Due to the relatively short half-life of vitamin C, it is possible to maintain higher blood levels if you supplement it multiple times per day instead of just once.
Because of this, it could theoretically have more of an impact if you had 1g of vitamin C 3x per day instead of just having it once.
If we are seeing small improvements with slightly lower dosages and single frequency timing, potentially we could see larger improvements with a slightly altered protocol.
Vitamin D
Sub-optimal vitamin D status is common in the general population and among athletes.
In athletes, the prevalence of deficiency depends on a variety of factors. Since a large portion of our vitamin D comes from sun exposure, the main variable determining this is how much sunlight somebody gets. Other variables also matter too such as the time of year, dietary intake and also skin colour.
Although there is a cut-off category for deficient and not-deficient, I think it is better to think of vitamin D through the ranges listed below.
There are many reasons why vitamin D can help with immune function. For example, it can stimulate antimicrobial peptides and help defend against pathogenic bacteria, fungi and viruses.
Lower vitamin D levels are associated with an increased risk of upper respiratory illness in athletes. In the research just linked, further reductions in these illnesses continued to occur up to as high as 95nmol/L.
Although there is this association between low vitamin D and illness, the obvious question is: Would supplementing help this?
The short answer is very likely yes.
A 2017 meta-analysis including 10,933 study participants concluded that vitamin D supplementation did reduce the risk of acute respiratory tract infection.
This effect was more pronounced in those who had low levels (<25nmol/L) before supplementation and in those who had not been undergoing regular supplementation.
Avoiding LEA
Low energy availability (LEA) is a state in which the body does not have enough calories left to support all physiological functions needed to maintain optimal health.
This is often due to a higher exercise/training volume, combined with an insufficient intake of calories to match that exercise.
Low energy availability can have both short-term and long-term outcomes.
There is evidence that low-energy availability contributes to an increased risk of illness.
The simple explanation for this is that if the body does not have enough calories/resources to support basic functions, less energy will be directed towards immune function.
This could also be combined with a bunch of other explanations too, related to diet or exercise factors that could contribute.
For context, some research has linked LEA with a 4-8x increased risk of upper respiratory tract infections in high level athletes.
Zinc
The research on zinc and immunity has been quite mixed.
Normally, systematic reviews and meta-analyses are considered the gold standard of research.
A 2017 meta-analysis of all the research on zinc lozenges had very positive findings. If these lozenges containing 75mg/day of elemental zinc were taken daily within 24 hours of symptom onset, upper respiratory tract symptom duration was reduced by 33% (~3 days).
The proposed mechanism was that zinc can act as an antiviral agent, as well as also having some anti-inflammatory and antioxidant properties.
Making it a bit more complex though is that a 2020 randomised controlled trial containing 88 participants undergoing a similar intervention found no difference.
And just to chuck a bit of a curveball out there too, there is an interesting study from 1987 where a zinc group had an INCREASED symptom duration of 5 days.
That study kind of highlights how sometimes random chance plays a role, particularly with small sample sizes.
If we see a reduction in symptom duration of 1-2 days, was that zinc? Or was it unrelated? Vice versa, if there is an increased duration, do we pinpoint that down to zinc? Or was it unrelated?
The key takeaway is that while some research looks promising for zinc and immunity, it is not consistently confirmed to be beneficial.
Avoiding Iron Deficiency Anaemia
While iron is typically not a nutrient that comes to mind when people are thinking of nutrition for immunity, it can still play a role.
There are certain aspects of immunity that require iron. T-lymphocytes in particular need large amounts of iron. If iron levels are low, they are less able to carry out their role in fighting viral infections.
Backing this claim up, there is evidence that when people have iron deficiency anaemia, it can impact immune function negatively.
Garlic
Garlic contains some compounds that can help the immune system.
The most well-known of these is alliin, which turns into allicin when chewed/crushed.
Individual studies have found that garlic can reduce both the frequency of illness and the duration/severity.
It is likely that garlic helps more with prevention than recovery from illness though.
The most well-designed study on this topic had 146 participants who received either a garlic supplement or placebo for 3 months. In this study, they found a 63% reduced likelihood of getting sick. Recovery time was relatively similar between groups.
Dosage and How to Take:
A common recommendation that has worked well in the research is 2 cloves of garlic, consumed two 2x per day (so 4 cloves total).
If using aged garlic extract instead, dosages used in research have ranged from 240–2560mg.
Echinacea
Cell studies have found that echinacea can destroy influenza viruses. This sounds promising, but cell studies are obviously less relevant than human studies.
There are some individual studies that have found that echinacea might reduce the risk of catching a cold, while also improving the recovery rate.
While individual studies have found that, it is not really a fair reflection of the research to say that echinacea is consistently effective.
Other researchers have concluded that a lot of the research on echinacea has been poorly designed. A review on this topic found that there is slightly positive evidence that echinacea outperforms placebo for treating and preventing colds.
Practical Summary
As you can tell, even with a perfect strategy, complete immunity to illness is unattainable. There are certain steps that can help with prevention and treatment though.
Including some of the things mentioned in this post could mean that you can spend more time training and competing effectively.
