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Probiotics for athletes: what’s the latest thinking?
Just how beneficial are probiotics for athlete health and performance, and should athletes be using them? SPB reports on brand new and definitive evidence
If you’re a regular subscriber, you’ll be well aware that immunity, and how to improve it, is a topic we have discussed on many occasions here at SPB. But why does immunity matter so much to athletes? Well firstly, there’s incontrovertible evidence that immunity and vigorous exercise are linked - with something of a double-edged sword relationship. If you exercise regularly, you will likely have improved immune function compared to your sedentary counterparts. Indeed, regular vigorous exercise may even prevent or reverse the age-related decline in immunity observed in the population at large(1).
On the flipside, heavy or prolonged bouts of exercise – eg running a marathon - generates a type of post-exercise immune depression sometimes referred to as ‘open window’ following the strenuous effort(2). This immune dip creates favorable conditions for upper respiratory tract infections (URTIs – coughs, colds, sore throats etc) to take hold in the days following a hard effort(3,4). Research shows that such an immune dip can lead to a 2- to 6-fold increase in the risk of upper respiratory tract infections, ultimately hurting an athlete’s performance(5).
Immunity matters
However, beyond the inconvenience and unpleasantness of being unwell, there’s a more profound link between immunity and athletic performance, which is lost training time. When you’re unwell, you either cannot train at all, or at the very best, cannot train properly. That 5-day cold and sore throat preventing you from training might also require 2-3 of days of easy training afterwards in order to ensure proper recovery. That’s a week of high-quality training missed. A couple of colds per year results in at least two weeks of missed training. Meanwhile, a bad bout of influenza can easily knock you out for a month.
Seasoned athletes seeking a new PB are often happy to improve their race times by just 1% over a season - eg runners dropping half a minute off a 40-minute 10km run time or cyclists slicing three quarters of a minute from a previous best of 70 minutes in a 25-mile time trial. Imagine how much easier it might be to achieve that new PB if you weren’t regularly losing 5-10% of your annual high-quality training time? This is why strategies aimed at improving immune function and reducing lost training time should be considered an integral and crucial part of successful training programs!
Nutrition and post-exercise immunity
There’s now good evidence that certain nutritional strategies can mitigate the stress in the immune system generated by exercise. These strategies have long included the use of such nutrients such as protein, carbohydrate, amino acids and vitamins/minerals during and after exercise (for a more in-depth discussion, readers are advised to see this article)(6,7). In more recent years however, there’s been an increasing interest in the use of probiotic supplements for enhancing athlete immunity.
As we have discussed in previous SPB articles, a growing body of research has demonstrated that the use of probiotic supplementation produces immune and gastrointestinal system benefits. These include:
· An increase in circulating leucocytes (key cellular components of the immune system)(8).
· Stimulation of the maturation of immune cells present in the gut, such as lymphocytes, macrophages, and dendritic cells(9).
· With certain strains of probiotics (eg Lactobacillus casei and Lactobacillus fermentium), a reduced risk of URTIs and flu-like symptoms, and an increase in the concentration of a key immune antibody known as ‘sIgA’ (the body’s first line of defence against pathogens) in gut mucosal tissues(10).
Just to recap, ‘probiotics’ is a generic term for a range of friendly bacteria that reside in the gut and enhance gut health. These bacteria are believed to work by balancing the bacteria in the gut (ie keeping harmful bacteria at bay), synthesizing key nutrients, strengthening the intestinal lining, and helping the immune system respond more effectively to stress(11). However, despite the evidence for the benefits of probiotics in human health (and particularly) immune function, data from studies on their effectiveness is rather variable.
Probiotic uncertainties
While many individual studies have shown that probiotics can reduce inflammation and boost immunity, the overall evidence has been somewhat confusing. Some studies show great benefits, while others show none at all(12). This variability is most likely due to fact that different studies have used different probiotic strains and combinations at different doses, in different athlete populations, for different durations, and sometimes with additional nutrients(13). A good example of this is that the probiotics Lactobacillus casei Shirota and Lactobacillus fermentum PCC are both believed to help boost immune activity, but the exact immune system elements (eg macrophages, T-cells, interferon, B-cells etc) they stimulate differ greatly from one another(14). You can think of different breeds of dogs as an analogy; yes they’re all dogs but the different breeds have different behaviour and temperament traits, which is why dog owners tend to get on better with some breeds than others!
New research
In science, when there is uncertainty about research findings, a common approach is to carry out a ‘meta-analysis’, which brings together all the previous research on a topic or aspect of a topic, pools all the findings then uses statistical analysis to reach a more scientifically robust overall conclusion. When it comes to probiotics however, the huge numbers of probiotic variants tested in different studies has resulted in different meta-analyses reaching different conclusions(15). What’s needed in this case is something called an ‘umbrella review’ This is an even higher-level study that doesn’t just look at individual meta-analyses (which are already summaries of multiple trials); it combines them into one giant overview, thereby helping to overcome the uncertainties caused by previous study variations. And now thanks to new research by a team of Chinese researchers, we can turn to new research - an umbrella review of probiotic use in athletes for some definitive answers(16).
What they did
Published in the journal ‘PeerJ’, this study set out to comprehensively identify all the relevant previous meta-analyses and recent individual studies published up until December 2025, and which focussed on the populations of athletes undergoing an intervention of probiotic ingestion. To do this, the researchers searched five major medical databases for all the relevant meta-analyses and standalone studies using the following criteria:
· Participants - included both amateur and professional athletes in good health, with no chronic immunological disorders or acute infections, and who were engaged in systematic training and organized competitions. Studies containing occasional participants or individuals without regular training were excluded.
· Probiotic supplementation - in any form (e.g., capsules, powder, fortified food) regardless of strain, dosage, or duration. No minimum dosage threshold was applied; however, all strain types, dosages (CFU – colony-forming units), and intervention periods were extracted and reported.
· Comparison – must have compared probiotic use to a placebo or no intervention.
· Outcomes- must have measured changes in immune and inflammatory biomarkers, including:
• Pro-inflammatory cytokines: TNF-α, IL-6, IL-8 (immune signalling molecules that are used to control inflammation).
• Anti-inflammatory cytokine: IL-10 (an immune signalling molecule that dampens down inflammation).
• Immunoglobulin: salivary IgA (an antibody found in saliva that acts as the first line of defense.
• Interferon: IFN-γ (a protein that helps the body fight off viruses).
• Acute-phase protein: CRP (a marker of general inflammation).
· Study design – must have been published in English or Chinese and provided enough data for a meaningful statistical analysis
In summary, this umbrella analysis incorporated five meta-analyses (encompassing 69 individual randomized controlled trials) and one additional recent trial, totalling 3,413 participants.
What they found
Once the (massive amount!) of data was sifted and statistically analyzed, a number of clear findings emerged, which revealed that probiotics do have a significant impact on an athlete’s body, but only on specific aspects of immunity:
• TNF- α - Firstly, and very relevant for athletes in training, was that probiotic ingestion significantly reduced levels of TNF-α. High levels of TNF-α serve as the body’s ‘general inflammation alarm’, indicating increased stress and inflammation; Reduced TNF-α levels from probiotic supplementation suggests reduced stress and inflammation, thereby allowing athletes to recover faster, and with less chronic inflammation-related wear and tear associating with serious training.
• IL-6/8 - By contrast, probiotic ingestion seemed to have no significant effect on two other inflammatory markers, IL-6 and IL-8. This was surprising because it contradicted some previous on probiotics and inflammation. The researchers therefore concluded that while probiotics can reduce inflammation overall, they might not change every specific signal in the inflammatory process.
• IgA - Another important finding was that probiotic use enhanced levels of salivary IgA. IgA is one of the body’s first lines of defences against viruses and bacteria entering the mouth and throat, helping to kill them before they have a chance to infect you generally. Since intensive exercise is known to reduce immunity (contributing to the open window period of infection risk), the ability of probiotics to boost IgA is a major plus for athletes trying to stay healthy during a season!
• IFN-γ – probiotic use significantly increased levels of IFN-γ, which is an immune protein that activates the immune cells that kill viruses. Higher levels of suggests that probiotics actively help the body stay ready to fight off infections that might evade the first lines of defense.
• IL-10 – probiotic ingestion didn’t seem to affect levels of another marker called IL-10. Because IL-10 is an anti-inflammatory immune molecule, the researchers concluded that probiotics produce an overall anti-inflammatory effect by turning down pro-inflammatory signals rather than just turning up the anti-inflammatory ones.
Although the overall combined results above were positive well supported by the data, the researchers cautioned that the results varied quite a bit from person to person and from meta-study to meta-study. This is likely because (as mentioned earlier), different probiotics seem to produce different benefits, depending on which species/strain is used. Moreover, the doses used in these studies varied greatly, and on top of that, individuality almost certainly plays a role. In simple terms, all of us have a unique gut microbiome (ie the types, quantities and ratios of bacteria living in our gut), which is affected by sleep, exercise, diet and genetics(17). This means that even with the same probiotic at the same dose, different athletes will likely experience some variation in responses.
Practical implications for athletes
What this new research shows is that despite the considerable variations shown in previous probiotic studies, the evidence overall strongly points to real benefits for athletes taking probiotic supplements. These benefits involve improved mucosal immunity (ie higher levels of IgA), which helps prevent URTIs from gaining hold, and a better immune response courtesy of IFN-γ should an infection occur. This combined immune protection equates to fewer sickness episodes, and shorter and milder episodes if they do occur. On top of that, probiotic use seems able to tone down the overall level of body-wide inflammation (indicated by TNF-α), which can help lower metabolic stress, thereby aiding recovery.
Unlike a number of other sports supplements claiming to ‘improve athlete health and performance’, the growing body of data from probiotic studies provides compelling evidence for their routine use. Along with a high-quality multi-vitamin/mineral supplement to cover any dietary shortfalls, probiotics should be regarded as a wise investment for athletes seeking to keep well, especially during the winter months or when trying to avoid a dip in immunity/URTIs following a particularly strenuous event/training effort! Here then are some tips for athletes wishing to use probiotic supplementation:
· Use bacteria strains that have proven to be effective in various studies such as Lactobacillus acidophilus, Lactobacillus paracasei, Bifidobacterium bifidum, Lactobacillus fermentum, Lactobacillus rhamnosus, Lactiplantibacillus plantarum and Lactobacillus casei.
· Probiotics in liquid form are more likely to be effective than dried forms such as capsules.
· Take any probiotic on an empty tummy and at least 15 minutes before food. A good time is soon after rising in the morning, but before breakfast.
· Any probiotic supplement needs to be taken for 30 days or more before exerting a beneficial effect (bear this in mind if you have a particular event or period of heavy training in mind). Probiotics are not a ‘quick fix’ for boosting immunity!
· Use a probiotic containing a blend of strains rather than a single strain.
· Ensure the strength of the probiotic is standardized and adequate (at least 5 billion CFUs per day).
· Probiotics are definitely recommended following a course of antibiotic treatment.
References
1. Front Immunol. 2021 Apr 16;12:639308
2. Sports Med. 2007, 37, 412–415
3. J. Sci. Med. Sport 2010, 13, e85–e86
4. J. Sports Med. 1997, 18, 91–100
5. Guimarães TT, Coelho W, Rubini E. 2022. Excesso de exercício físico. In: Brazilian Journals Editora, volume 1
6. Nutr. Rev. 2008, 66, 310–320
7. Exerc. Immunol. Rev. 2017, 23, 8–50
8. Br. J. Sports Med. 2006, 40, 351–35
9. Exerc. Immunol. Rev. 2015, 21, 70–79
10. Synth. Syst. Biotechnol. 2018, 3, 113–120
11. Nutrients 2023. 15(9):2114
12. Journal of Sport and Health Science 2024. 13(1):61-71
13. Nutrients 2017, 9, 1021
14. Archives of Medical Research 2021. Vol52 6 P582-594
15. Applied Sciences 2023. 13(6):3448
16. PeerJ. 2026 Feb 26:14:e20809. doi: 10.7717/peerj.20809. eCollection 2026
17. Advances in Nutrition 2021. 12(6):2190-2215
Andrew Hamilton
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