Effects of a strain-specific probiotic formulation on subjective sleep quality: a randomized, double-blind study

The intestinal microbiota has been implicated in neurological function through the gut–brain axis, and specific probiotic strains have been proposed to influence neuroactive pathways relevant to sleep. This randomized, double-blind, study enrolled 60 otherwise healthy adults reporting poor subjective sleep quality. Sixty participants (mean age 22.0 ± 3.0 years) were randomized to receive either a probiotic formulation (Lactobacillus rhamnosus HN001, L. rhamnosus SP1, L. acidophilus LA1, L. reuteri LR92; total daily dose 6×10⁹ CFU) or a matched non-bacterial comparator for six weeks, followed by three-week washout period. Sleep quality was evaluated using the Pittsburgh Sleep Quality Index (PSQI) and the Insomnia Severity Index (ISI) at baseline (T0), 3 weeks (T1), 6 weeks (T2), and after a 3-week washout (T3). Compared with the matched non-bacterial formulation, participants receiving the probiotic formulation showed a significant improvement in subjective sleep quality at T2 and T3, as assessed by between-group non-parametric analyses. PSQI scores in the probiotic group decreased from 19.2 ± 3.1 at baseline to 7.5 ± 3.9 at week 6, with improvements exceeding the minimal clinically important difference. Similar temporal patterns were observed for ISI scores. Benefits persisted through washout; however, the mechanisms underlying this persistence remain speculative. These findings suggest that supplementation with a targeted multi-strain Lactobacillus spp. formulation may provide additional benefits on perceived sleep quality when added to a matched non-bacterial formulation. Given the use of subjective sleep measures and the absence of microbiome or objective sleep assessments, further studies integrating polysomnography or actigraphy and microbiota profiling are required to confirm these results and clarify the underlying mechanisms.