THE ARISING · Longevity & Healthspan
Probiotics Linked to Better Mood and Sleep; Anxiety Benefits Remain Unclear
Pooled results from 20 placebo-controlled trials show that probiotic supplements lowered depression scores and improved sleep quality in healthy adults, but did not significantly change anxiety.
The findings come from a systematic review and meta-analysis published in Pharmacological Research online on October 29, 2026 by Liu Q and colleagues at Southwest Medical University in China. A meta-analysis combines results from separate trials into a pooled estimate. Its reliability depends on the quality and comparability of the included studies. This one covered 1,508 participants. Each trial was a randomized controlled trial that compared probiotics with placebo for at least four weeks.
For depression, probiotics reduced scores by a standardized mean difference of −0.23 (95% confidence interval −0.36 to −0.10). That is a small effect. The trials agreed closely with each other, with very little variation between them (I² of 4.67%).
For sleep quality, the effect was larger. The standardized mean difference was −0.37 (95% confidence interval −0.52 to −0.22), with moderate variation between trials (I² of 41.67%). The authors report that probiotics improved sleep quality.
Anxiety told a different story. The overall effect was not significant (standardized mean difference −0.11, 95% confidence interval −0.31 to 0.09, P = 0.27). The trials also disagreed more on this outcome (I² of 61.41%).
The researchers used the GRADE system to rate how far the evidence can be trusted. Certainty was moderate for depression and for sleep quality. It was very low for anxiety. The authors conclude that probiotics may alleviate depressive symptoms and improve sleep in healthy adults, while the effect on anxiety remains inconclusive.
The participants were healthy adults, so the results speak to everyday mood and sleep, not to treating diagnosed illness. The authors say no firm conclusion can be drawn about how long supplements should be taken or which strains work best. Those questions were explored in subgroup analyses that were not adjusted for multiple comparisons.
The authors call for larger, standardized randomized trials to confirm the findings and to sort out which strains drive any effect.
Source: Liu and colleagues, Pharmacological Research, October 29, 2026.