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Abstract
Chronic insomnia may involve a complex interaction between immune pathways, circadian rhythms, and the melatonin system.
- Chronic insomnia has been linked to central hyperarousal and sleep-wake rhythm misalignment, though these ideas lack strong clinical backing.
- Mast cells are identified as key immune cells involved in the interactions among immune-inflammatory pathways, circadian timing, and melatonin.
- Hydrogen's potential sleep-improving effects may arise from its antioxidant, anti-inflammatory, and mitochondrial protective properties.
- Direct evidence that hydrogen targets the mast cell-sleep-wake rhythm-melatonin triad is currently lacking.
- Existing studies on hydrogen's effects on sleep are inconsistent, context-dependent, and often limited by methodological issues.
- The review outlines the need for further research to clarify the indirect pathways through which hydrogen may influence sleep disorders.
Simplified
The pathogenesis of sleep disorders, particularly chronic insomnia, obstructive sleep apnea (OSA), and sleep fragmentation (a symptom within the spectrum of chronic sleep deprivation-related sleep disturbances, rather than an independent diagnostic sleep disorder entity; e.g., as seen comorbidly with restless legs syndrome (RLS))-defined as a prolonged reduction in total sleep time (< 6 h per night) or sleep efficiency (< 85%) for ≥ 3 months, consistent with the International Classification of Sleep Disorders, 3rd Edition (ICSD-3) diagnostic criteria-is closely associated with the dysregulated crosstalk among immune-inflammatory pathways, the circadian timing system, and the melatonin system, with mast cells serving as one of the key immune cell types involved in this network. Notably, chronic insomnia has been linked in conceptual models to central hyperarousal and sleep-wake rhythm misalignment, yet these constructs remain debated in contemporary sleep science and lack definitive, universal support from high-level clinical evidence and systematic reviews. As a narrative review, this article focuses on the interactions among these three, summarizes the current understanding of the sleep-wake rhythm-dependent dual-pathway regulation of mast cell activation, the oscillatory coupling between sleep-wake rhythm genes and mast cell functions, as well as the mediating role of the melatonin system. Additionally, by integrating the associations between inflammatory mediators and related pathological processes (such as iron metabolism disorders and mitochondrial dysfunction) with sleep disorders, it explores the potential indirect and non-specific mechanisms underlying hydrogen-induced sleep improvement. Notably, direct experimental evidence that hydrogen specifically targets the mast cell-sleep-wake rhythm-melatonin triad remains critically lacking. Its sleep-improving effects are currently hypothesized to be mediated by antioxidant, anti-inflammatory, and mitochondrial protective properties, which may permissively support the function of the circadian timing system and sleep homeostatic/arousal systems rather than directly engaging the core transcriptional-translational feedback loop (TTFL) of the circadian clock system. Although hydrogen does not act as a canonical chronobiotic that directly targets the TTFL, it may exert indirect chronobiotic properties by optimizing intracellular redox balance and reducing oxidative stress-conditions that are essential for maintaining the robustness, amplitude, and stability of circadian clock function. However, this indirect chronobiotic potential remains largely theoretical and is supported only by limited indirect evidence, with no definitive data confirming that hydrogen can directly reset, phase-shift, or entrain the core circadian clock machinery. Notably, these indirect effects are hypothesized to be context-dependent: hydrogen may alleviate sleep disturbances linked to oxidative stress and inflammation (e.g., insomnia secondary to chronic stress, OSA-associated sleep fragmentation (a symptom secondary to multiple sleep disorders rather than an independent sleep disorder, e.g., RLS)) but is unlikely to target the distinct pathophysiological drivers of other sleep disorders (e.g., sensory-motor dysfunction in RLS, ventilatory control defects in OSA). Therefore, any causal claim that hydrogen directly regulates this triad must be regarded as speculative and not yet supported by empirical data. This distinguishes hydrogen from classic chronobiotics (e.g., melatonin, CK1ε/δ inhibitors) that directly target the TTFL machinery. We conducted literature retrieval from PubMed and CNKI, incorporating relevant Chinese and English studies published in the past decade for logical integration and evidence analysis. Existing evidence suggests that hydrogen may exert potential sleep-related effects in certain contexts, but these findings are inconsistent, context-dependent, and limited by methodological shortcomings-including small sample sizes, short intervention durations, lack of objective sleep metrics, and unaddressed placebo effects. Given the heterogeneous pathophysiology of sleep disorders (e.g., subjective hyperarousal in insomnia, breathing abnormalities in OSA, leg motor sensations in RLS), hydrogen's non-specific antioxidant/anti-inflammatory actions cannot explain the full spectrum of these conditions, nor does current evidence support that hydrogen-based interventions are superior to established therapies (e.g., cognitive behavioral therapy for insomnia, nasal continuous positive airway pressure for OSA). Nevertheless, this narrative review provides a novel theoretical framework integrating hydrogen with the mast cell‑sleep‑wake rhythm‑melatonin axis, identifies shared pathological targets (oxidative stress, mitochondrial dysfunction, neuroinflammation) across inflammation‑related sleep disturbances, and highlights testable mechanistic hypotheses and translational directions that fill current knowledge gaps in adjuvant sleep disorder research, thereby constituting meaningful scientific impact complementary to first‑line therapies. Moreover, these findings are primarily downstream, integrative phenomena and do not establish a causal link to specific cellular targets (e.g., mast cells) or sleep-wake rhythm biological mechanisms. There are gaps in clinical trials, along with theoretical limitations including multi-target effects, species differences, and placebo effects, and the absence of direct molecular/cellular evidence for hydrogen targeting the mast cell-sleep-wake rhythm-melatonin system. Future studies with large samples and technological innovations are needed to clarify its potential efficacy and the indirect regulatory pathways linking hydrogen to the mast cell-sleep-wake rhythm-melatonin network, thereby providing a scientific basis for the potential clinical application of hydrogen in the intervention of sleep disorders.