This randomized double-blind, placebo-controlled trial investigated the effects of BLa80 on sleep quality, employing both subjective measures (PSQI and ISI scores) and objective analyses of gut microbiota and in vitro GABA production. This approach provides a framework for assessing the therapeutic potential of BLa80 as a safer alternative to conventional sleep aids, which are often associated with significant side effects and dependency risks [4].
In our study, the Pittsburgh Sleep Quality Index (PSQI) and the Insomnia Severity Index (ISI) served as primary tools for measuring subjective sleep quality. The reliability of these questionnaires in assessing sleep disorders has been well recognised and verified within clinical research [16]. However, it is crucial to acknowledge the inherent limitations associated with self-reported data, which can be influenced by various factors, including cognitive biases, current emotional state, and societal perceptions of health interventions. Currently, the widespread popularity of probiotics and the public's strong belief in their health benefits could potentially influence participants' subjective responses in studies evaluating their effects [17]. Interestingly, a previous study employing magnetic resonance imaging to explore the influence of probiotics on mood demonstrated significant changes even within the placebo group [18]. This suggests that the placebo effect was not only reflected in subjective scores, but also in objective data. Self-reports are susceptible to interference from a variety of factors such as current situations, nonverbal cues, and memory biases. This finding underscores the complexity of the placebo effect, which not only impacts subjective assessments but can also manifest in objective measurements, suggesting a psychophysiological response to the placebo intervention. In this trial, both the BLa80 and placebo groups exhibited notable reductions in PSQI and ISI scores, indicative of improved sleep quality. Although these advancements show potential, it is important to approach them with caution because there is a possibility of a placebo effect, which is a frequently observed occurrence in experiments that involve subjective outcomes [19]. Despite the reported improvements in clinical outcomes, this effect was still apparent, emphasising the importance of implementing strict controls and objective metrics in future research to distinguish genuine therapeutic advantages from placebo reactions.
Given the inherent limitations of self-report measures, which have long been scrutinized by psychologists and psychiatrists for their accuracy, this study also incorporated objective analyses of gut microbiota and GABA production. BLa80 intervention notably increased beta diversity and reduced the Proteobacteria population at the phylum level, aligning with evidence that dysbiosis in the gut microbiome may be linked to psychiatric disorders. This suggests potential therapeutic and preventative applications for gut microbiome modulation. For instance, Jiang et al. reported elevated levels of Proteobacteria and Enterobacteriaceae in patients with depressive disorders compared to healthy controls [20], highlighting the association between microbial imbalances and mental health. The instability often seen in the Proteobacteria phylum can indicate an imbalance or structural instability within the gut microbial community, necessitating further investigation into the causes of these fluctuations to develop effective interventions [21].
At the genus level, BLa80 notably enhanced pathways related to purine metabolism, glycolysis/gluconeogenesis, and arginine biosynthesis, which are crucial metabolic pathways implicated in mental health [22]. Literature demonstrates a strong association between abnormalities in purine and pyrimidine metabolism and various psychiatric conditions including anxiety, depression, and sleep disorders [23]. Previous studies have also connected the dysregulation of these metabolic pathways with depressive symptoms and sleep disturbances [24–26], and even broader cognitive dysfunctions, such as those seen in neurodegenerative diseases and Alzheimer's disease. Our findings suggest that the modulation of these metabolic pathways by BLa80 could contribute to the observed improvements in sleep quality. This hypothesis is supported by the intervention's impact on purine and pyrimidine metabolism, providing a potential mechanism for its effects on both gut health and sleep quality, underscoring the integrated role of metabolic pathways in neuropsychiatric health. Arginine biosynthesis has been identified as significantly linked with stress management, which is crucial considering stress's role as a predominant factor in the onset of insomnia episodes [27]. This connection underscores how BLa80 may influence sleep quality through the modulation of neurotransmitters involved in stress responses.
On another note, gamma-aminobutyric acid (GABA) serves as the central nervous system's primary inhibitory neurotransmitter, regulating key physiological processes including the sleep-wake cycle, motor functions, and vascular tone. GABA contributes to brain homeostasis and function by binding to its receptors and reducing neuronal excitability. In the realm of probiotics, Bifidobacterium bifidum is renowned for its potent GABA-producing capabilities. Research indicates that Bifidobacteria can generate up to 6 g/L of GABA during growth, positioning it as a promising probiotic for boosting GABA levels through dietary intake or supplements, thus offering substantial health benefits. To explore the GABA-producing capability of BLa80, an in vitro experiment was conducted using a liquid chromatography method that confirmed BLa80's capacity to produce GABA. Based on these findings, there is potential to optimize the fermentation medium or employ fecal co-culture techniques to further assess GABA production. The ability of BLa80 to synthesize GABA is not only pertinent to its impact on host health but also opens new avenues for treating neuropsychiatric disorders. Consequently, the GABA synthesizing ability of BLa80 may be a significant aspect of its probiotic potential, offering insights into innovative strategies for managing sleep disorders and enhancing mental health.
Our study has identified key limitations that need to be addressed in subsequent research. The demographic restriction to young and middle-aged Chinese participants and potential gender disparities in the treatment group suggest that our findings may not be universally applicable. Besides, as our previous research supported the assumption, the fecal sample at T0 were not collected [28]. The absence of initial fecal samples limited the scope for pre- and post-intervention comparisons. Furthermore, future studies should consider a more diverse demographic and increase the number of sampling points to accurately reflect the dynamic nature of gut microbiota changes. Additionally, the influence of dietary variations on gut microbiota underscores the necessity for stricter dietary controls in future trials to better isolate and understand the specific effects of probiotic interventions on gut health.