Comment letter on ‘gut microbiota, circadian rhythms and their interactions: implications for the pathogenesis and treatment of depression’

The emerging field of microbiome-circadian-psychiatry research has generated considerable interest, yet the translation of laboratory findings into clinical practice remains challenging. The study conducted by Du et al. provides a comprehensive overview of gut microbiota and circadian rhythm interactions in depression, synthesizing complex biological pathways into potential therapeutic frameworks. While the authors present a valuable integration of diverse research streams, we respectfully highlight critical areas that warrant refinement to enhance the manuscript’s scientific rigour.

Firstly, the manuscript presents an overly optimistic portrayal of probiotic interventions for depression that contradicts recent high-quality evidence. The authors describe probiotics as having ‘significant antidepressant effects’ without adequate acknowledgment of substantial research limitations. Recent meta-analyses [1,2] demonstrate that probiotics are effective in reducing depressive symptoms when administered in addition to antidepressants (SMD = 0.83, 95%CI 0.49–1.17), however, they do not seem to offer significant benefits when used as stand-alone treatment (SMD = −0.02, 95%CI −0.34 to 0.30). Additionally, meta-analysis of five studies demonstrated no significant improvement in depressive symptoms in subjects receiving probiotics in paediatric populations (SMD = 0.04, 95% CI: −0.33 to 0.41, p = 0.84).

This evidence contradicts the manuscript’s broadly optimistic claims and highlights critical gaps in standardization including optimal bacterial strains, dosing protocols, and treatment duration. The authors should provide balanced reporting of effect sizes with confidence intervals and acknowledge the preliminary nature of current evidence.

Secondly, this study discusses FMT as a promising therapeutic intervention without adequate consideration of safety, regulatory, and ethical complexities specific to psychiatric applications. Current FMT protocols remain primarily validated for recurrent C. difficile infections, with limited safety data for psychiatric indications [3,4].

Professional standards require clear distinction between established clinical applications and investigational uses. The manuscript overlooks critical implementation challenges including donor screening protocols for neuropsychiatric applications, cost-effectiveness considerations, and regulatory approval pathways for psychiatric indications.

Thirdly, attributing therapeutic effects of circadian interventions (light therapy, melatonin) primarily to gut microbiota modulation, representing a reductionist interpretation that may mislead readers about these treatments’ complex, multi-system nature.

Contemporary research demonstrates that light therapy’s antidepressant effects primarily involve direct neuroendocrine pathways, with microbiota changes likely representing secondary phenomena rather than primary mechanisms. This mechanistic oversimplification could impact treatment selection and patient counselling, necessitating more nuanced understanding of multiple parallel therapeutic pathways.

In summary, while this manuscript addresses an important evolving field, these revisions would enhance scientific rigour while maintaining its valuable contribution to understanding gut-brain-circadian interactions in depression.

Funding Statement

Both authors reported that this work received no financial support.

Disclosure statement

Shuya Tang and Lei Liu declare no conflict of interest to disclose.

Data availability statement

Data sharing is not applicable to this article as no datasets were generated during current study.