With almost all supplements that athletes take, the goal is for them to directly translate towards them being some variation on bigger, leaner, stronger and/or faster. And while there is debate about whether probiotics can contribute to those aspects, there is emerging research that is relatively compelling that probiotics can help improve immunity.
Improved immunity does not directly improve any of those characteristics. But if you are able to train more consistently, and also have less of your sessions impacted negatively by lingering illnesses, it is likely going to translate into improved performance.
Why Is This Relevant?
Upper respiratory tract infections (URTIs) appear to be the most relevant area where probiotics help improve outcomes.
Probiotics also have solid evidence when it comes to gastrointestinal concerns. But for this article, I want to keep a pretty narrow focus since I think the impact on URTIs is less well known.
A three-year study on >300 Olympic athletes highlighted that 70% of illnesses resulted in absences from training or competition. Other illnesses that didn’t result in missed time still impacted training negatively.
Illness impacting training/performance is a no-brainer. We don’t exactly need a study to prove that. But it is something that is important to pay attention to, since minimising the frequency and duration of illness is important if you are looking to optimise your outcomes.
Athletes who are training particularly hard can suffer from reduced immunity and a significantly increased risk of URTIs.
Small amounts of exercise typically improve immunity. Really pushing the envelope though can have the opposite effect. This is most commonly seen in endurance athletes. Particularly when the volume and intensity of training is at its highest.
The mucosal lining of the GI tract is the bodies first line of defence against pathogens and is therefore important for immunity.
Since high volumes of intense training negatively impacts immunity by reducing the number and function of immune cells, this becomes even more important.
Probiotic supplementation appears to offset this issue and improve the function of the immune system.
Probiotics also appear to have benefits beyond just the gut by improving interactions between gut bacteria and the host immune system in general.
What Does the Research Show?
At the time of writing, there is a total of 22 relevant studies on probiotic supplementation and immune related outcomes.
Of these studies, 14 reported a significant improvement, whereas 8 showed no noticeable difference.
This alone is typically enough to be of interest to most athletes. If there is a decent chance of improved outcomes, with no noticeable downside (outside of cost and inconvenience of taking a supplement), most athletes will go for it. Most athletes take supplements with less of an evidence base behind them.
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.
The theoretical reasoning behind this improvement was due to enhanced T-Lymphocyte function.
Another study using Lactobacillus casei Shirota showed significant reductions in frequency and duration of URTIs as well.
Most of the research has highlighted reductions in duration and frequency, but some research using also using Lactobacillus casei Shirota reported reductions in severity of symptoms.
Most of the research has been focused on endurance athletes since they appear to be most at risk of URTIs. But there is research on other sports.
A multi-strain probiotic was used in elite rugby union players and was shown to reduce the frequency and duration of infections.
In a study covering a wide variety of sports during winter, there was a reduction in duration and frequency as well when L. Helveticus was used.
Digging into the details it looks as though the majority of the research that did not have positive results was conducted outside of winter.
That makes things a bit more interesting. Almost all of the positive research appeared to be done during winter, which is when URTIs are typically more common.
The overall body of evidence is in favour of probiotics and immunity. If you wanted to only use them during specific times though, it makes more sense to use them for these purposes during winter than summer.
Beyond that, it also makes sense to time it so that it lines up with intense training loads. The impact is likely less significant during periods of time with lower training loads.
To borrow from The International Society of Sports Nutrition’s position stand:
The following strains/species have been shown to improve immune health in athletes, reducing the episodes, severity or duration of exercise-induced infections:
- 1.2 × 1010 CFU L. fermentum VRI-003 (PCC) at 1.2 × 1010 CFU and at 1 × 109 CFU in males;
- L. casei Shirota (LcS) at 6.5 × 109 CFU twice daily;
- L. delbrueckii bulgaricus, B. bifidum, and S. salivarus thermophilus at 4 × 1010 CFU administered in the form of a yogurt drink;
- B. animalis subsp. lactis BI-04 2 × 1010 CFU;
- L. gasseri 2.6 × 109 CFU, B. bifidum 0.2 × 109, and B. longum 0.2 × 109 CFU;
- B. bifidum W23, B. lactis W51, E. faecium W54, L. acidophilus W22, L. brevis W63, L. lactis W58 at 1 × 1010 CFU;
- L. helveticus Lafti L10 at 2 × 1010 CFU.
Therefore, I would use any of the above as a starting point. If you are purchasing a probiotic, I’d try to make sure it features at least one of these species in a sufficient amount.
There are readers of this blog from around the world, so it is hard to give a specific recommendation. Personally, I live in Australia and my current recommendation that fits the criteria above is Lifespace Immune Support, but there are a lot of options out there that work well.
As always, I think a food first approach is important. Do not take a probiotic and think of it as an excuse to not focus on your diet.
Having an overall nutritious diet is incredibly important for immune function and performance.
It is probably a good idea to have probiotic foods within your diet too. It is probably a good idea to consume some form of fermented foods such as:
The reason why I think it is worth discussing these supplements though is just because the evidence is starting to look so positive. Ignoring probiotic supplementation could mean you are unnecessarily missing training days or underperforming due to more frequent/prolonged illnesses.