Probiotics

Summary

What is it? Probiotics are live microorganisms, mostly bacteria, sold as supplements. A synbiotic combines them with a prebiotic, a substance such as inulin that feeds the bacteria ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

Why would I need it? Many people want to know whether probiotics can improve sleep. The idea is that gut bacteria send signals to the brain, a link known as the gut-brain axis. Athletes are of particular interest, because hard training and competition often disturb their sleep ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

Is it useful? For sleep, the evidence is weak. So far this page covers one review of six small trials in athletes and other trained people. It found a hint of better self-rated sleep, and little data from sleep measured by devices. The authors call the evidence limited and ask for larger trials ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}. In the general population, a 2024 meta-analysis also found better self-rated sleep with probiotics ^{[2]Effects of probiotics on sleep parameters: A systematic review and meta-analysis. Ito H, Tomura Y, Kitagawa Y, et al. Clin Nutr ESPEN, 2024}.

FAQ

Do probiotics improve sleep? Perhaps slightly, as people rate it themselves. A meta-analysis of 15 trials in the general population found better scores on the Pittsburgh Sleep Quality Index (PSQI), a standard sleep questionnaire, after 4-6 weeks and after 8-16 weeks ^{[2]Effects of probiotics on sleep parameters: A systematic review and meta-analysis. Ito H, Tomura Y, Kitagawa Y, et al. Clin Nutr ESPEN, 2024}. In athletes, a review of six trials found that 9 of 12 sleep outcomes favoured the supplement, though not all of these results hold up ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

Do they work for athletes? This has not been shown yet. The six trials in athletes were small, and the review rated five of them "some concerns" and one "high risk" of bias ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}. See Probiotics for sleep in athletes: what the evidence says.

Do probiotics help you fall asleep faster? It is unclear. One probiotic trial in 15 dancers measured this and found no effect. One synbiotic trial found that soccer players fell asleep faster ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

How is a synbiotic different from a probiotic? A synbiotic also contains a prebiotic. The review included four probiotic trials and two synbiotic trials, too few to compare the two ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

Article

What it is

Probiotics are live microorganisms taken by mouth. Products differ widely in the strains they contain, and the effect may depend on the strain. So the result for one product does not necessarily apply to another ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

What the evidence says about sleep

A 2026 systematic review searched for randomised trials that gave probiotics or synbiotics to trained people and measured sleep. It found six trials, lasting 4 to 17 weeks ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}. Because the trials differed so much, the authors did not pool the data. Instead, they counted how many results pointed in a favourable direction ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

In the general population, a 2024 meta-analysis found lower (better) PSQI scores with probiotics than with placebo at 4-6 weeks and at 8-16 weeks, and some improvement on a second sleep questionnaire. It noted some risk of bias ^{[2]Effects of probiotics on sleep parameters: A systematic review and meta-analysis. Ito H, Tomura Y, Kitagawa Y, et al. Clin Nutr ESPEN, 2024}.

The athlete trials are described in detail on Probiotics for sleep in athletes: what the evidence says.

Products used in the athlete trials

CFU (colony-forming units) is a count of live bacteria. The review's table reports doses in different ways; the rugby figure is the total for the product ^{[1 Table 1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

Safety

The review reports no safety problems, but it does not list side effects trial by trial, and no other source was checked for this ^{[1]The effect of probiotic and synbiotic supplementation on sleep parameters in exercised population: a systematic review and synthesis without meta-analysis (SWiM) of randomized controlled trials. Salehi Asl M, Ahmadi F, Ershadmanesh M, et al. J Int Soc Sports Nutr, 2026}.

Talk to a doctor before you start a supplement, especially if you take medicines or are pregnant.

Verification

Checked on 2026-11-10.

See also

• Probiotics for sleep in athletes: what the evidence says