Acupuncture treatment for insomnia based on the microbiome–gut–brain axis theory: A review

Insomnia is a prevalent sleep disorder affecting between 19% and 50% of the global population, characterized by difficulty falling asleep or maintaining sleep, resulting in poor sleep quality and significant impacts on social functioning and patients' quality of life. This narrative review explores the mechanisms by which acupuncture, a therapeutic modality of traditional Chinese medicine, improves insomnia through modulation of the microbiota–gut–brain (MGB) axis.

The MGB axis represents a bidirectional communication system between the gut microbiome and the brain, operating through four main pathways: gut microbiota metabolites (especially short-chain fatty acids), the immune system, the neuroendocrine pathway, and the vagus nerve. The human gut microbiota contains between 10¹³ and 10¹⁸ microorganisms, with Firmicutes and Bacteroidetes representing approximately 92% of the human microbiome.

Research demonstrates that acupuncture can effectively regulate the ecological stability of the gut microbiota, balancing the proportion of probiotics and pathogens. Studies show that electroacupuncture increases the abundance of beneficial bacteria such as Lactobacillus and Bifidobacterium while reducing opportunistic pathogens. Acupuncture also modulates the levels of short-chain fatty acids (SCFAs), which play a vital role in sleep regulation by influencing neurotransmitters and circadian rhythms.

An important mechanism is acupuncture's ability to regulate the intestinal mucosal barrier and immune-mediated inflammation. When the balance of the gut microbiota is disturbed, intestinal barrier function is compromised, allowing bacterial metabolites to enter the systemic circulation and trigger inflammatory responses. Acupuncture has been shown to restore microbiota balance, increase the abundance of anti-inflammatory bacteria, and improve the integrity of the intestinal barrier.

Regulation of brain–gut peptides represents another crucial mechanism. Acupuncture influences the production of serotonin (5-HT), an essential neurotransmitter for sleep preparation, onset, and maintenance. Studies show that electroacupuncture can increase the abundance of probiotics that facilitate the conversion of tryptophan to 5-HT. Simultaneously, acupuncture can reduce levels of ghrelin, a peptide that promotes wakefulness and inhibits sleep.

The hypothalamic–pituitary–adrenal (HPA) axis is also modulated by acupuncture. Hyperactivity of this axis impairs sleep quality through sleep fragmentation and reduction of slow-wave sleep. Acupuncture has demonstrated the ability to regulate factors related to the HPA axis, reducing cortisol release and normalizing levels of corticotropin-releasing hormone.

Finally, acupuncture modulates the vagus nerve pathway, which serves as a communication channel between the central and enteric nervous systems. Acupuncture can increase vagus nerve activity and the expression of GABA type A receptors, thereby enhancing neurosuppressive effects and sleep quality.

From the perspective of traditional Chinese medicine, the theory that 'stomach disharmony leads to restless sleep' aligns with the modern theory of the MGB axis. The TCM concept of 'stomach' encompasses the entire digestive system and the Yangming meridians, which connect to the brain via the meridian network.

Despite significant advances, limitations persist in the current research, including a disproportionate focus on preclinical animal models, translational gaps between mechanistic insights and clinical applications, and a lack of long-term follow-up data on the durable therapeutic effects of acupuncture.