Art: N.S. Harsha, Detail from We Come, We Eat, We Sleep, 1999-2001
Healthy gut, healthy sleep
STUDY: Ren T et al, Front Nutr 2026;13:1795450
STUDY TYPE: Systematic review and meta-analysis
FUNDING: Independent
Background
Probiotics improve the healthy balance of bacteria in the gut. They affect the brain in many ways, influencing neurotransmitters, stress hormones, inflammation, vagal nerve signalling, and circadian rhythms… which brings us to this analysis of their effects on sleep.
The Study
Fourteen randomized trials involving 946 adults compared probiotic supplementation to placebo on sleep outcomes. Trials ranged from 4 to 52 weeks, used a variety of Bifidobacterium and Lactobacillus strains, and enrolled both healthy adults and those with poor sleep at baseline. The primary outcome was the Sleep Quality scale (PSQI); secondary outcomes included the Insomnia Severity Index (ISI), Epworth Sleepiness Scale (ESS), and serum cortisol.
Probiotics improved sleep quality (reduced PSQI scores by 0.59 points) compared to placebo. That’s a statistically significant effect but below the minimum clinically important difference of 1.5–3.0 points. Insomnia also improved modestly. Daytime sleepiness (ESS) and cortisol didn’t change.
Younger participants (under 30) showed larger effects than older ones. Strain, dosage, and duration varied widely across trials.
Practice Implications
- Probiotics have a small benefit on sleep, but small benefits can build, improving mental health over time.
- In other studies, they improve depression, anxiety, and cognition.
- Here are lab-tested products with the strains used in psychiatric studies, and a diet for gut health.
— Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
