A systematic review has been published nutrients, Researchers have described gut microbiota and metabolic changes common to metabolic syndrome (MetS) and sleep disorders.
Study: The microbiota-gut-brain axis in metabolic syndrome and sleep disorders: a systematic review.. Image Credit: Kmpzzz/Shutterstock.com
One of the main mediators of the association between sleep disorders and MetS is diet. Yet, scientific evidence about its effects on human metabolism and sleep is scarce.
Moreover, studies have not uncovered the biological mechanisms that regulate the complex crosstalk between neuroendocrine, immune, and metabolic pathways that link sleep disorders with MetS.
Furthermore, several factors such as smoking, alcohol consumption and poor diet can lead to gut dysbiosis, which adversely affects the gut-brain axis. However, the precise extent to which the gut microbiota influences sleep homeostasis and MetS remains unclear.
The researchers conducted two separate thorough literature searches in the Medline-PubMed database to review observational studies and randomized clinical trials (RCTs) investigating microbial composition in adults with MetS and sleep disorders over the past ten years.
The database search returned 117 articles, of which they selected 59 articles for the comprehensive full-text search. The final sample set consisted of 36 articles, 11 for sleep disorders and 25 for MetS.
The gut-brain axis
Communication between the gut and the brain is facilitated by multiple pathways. One such pathway includes the afferent vagus nerve, which enters the gut and sends signals to the central nervous system (CNS).
This nerve is responsive to various substances, such as microbial neurotransmitters, hormones, fatty acids, and cytokines.
Among the various neuromodulators, acetylcholine (ACh), norepinephrine (NE), and γ-aminobutyric acid (GABA) are particularly notable.
They are produced and metabolized by gut microbes, which play an important role in directly and indirectly stimulating connections between gut afferent neurons and the CNS.
Specifically, studies have identified that Lactobacillus and Bifidobacterium spp. strains can synthesize GABA. This synthesis affects neurological function including sleep disorders and memory modulation.
Additionally, the gut bacterium Clostridium sporogen converts tryptophan (Trp) to 5-hydroxy-tryptophan, a precursor to serotonin.
This conversion enhances the inhibitory neuroregulatory effects of L-tryptophan (TRP) by interacting with trace amine-related receptors.
Furthermore, the gut microbiome is involved in the neuroprotective effects of melatonin against cognitive impairment caused by sleep deprivation (SD), as demonstrated in mouse studies.
The gut microbiome influences immune cell activity both directly and indirectly, which contributes to circadian clock regulation.
For example, Lactobacillus rhamnosum can stimulate regulatory T-cells both indirectly through microbial cell wall components such as lipopolysaccharides (LPS) and directly through modulation of immune signaling through pattern-recognition receptors (PRRs).
Finally, gut microbes are known to modulate the expression of genes that regulate circadian rhythms, such as Rev-ERBA.
Host-microbial mechanisms influencing sleep disorders and MetS
Studies included in this review have shown how the internal biological clock (or circadian rhythm) alters metabolic homeostasis and that any changes in nutritional and metabolic status affect circadian rhythms; So, this link was reciprocal.
Furthermore, any disruption of the fine circadian pattern leads to internal dyssynchrony and organ failure, as commonly seen in sleep disorders, such as sleep apnea, narcolepsy, insomnia, and circadian rhythm sleep disorders, classified based on their clinical manifestations.
Several controlled trials have addressed the need to establish a cause-and-effect relationship between sleep duration and gastrointestinal (GI) disorders.
They found that gut microbial neurometabolites and amino acids, such as Trp and alpha-lactalbumin (A-LAC), influence the gut-brain axis of sleep.
Thus, many studies have shown that consuming Trp-rich foods, such as milk, is associated with improved sleep quality.
In an RCT, Schaafsma et al. found that three weeks of supplementing with a dairy-based product in subjects with sleep disorders effectively improved their Pittsburgh Sleep Quality Index (PSQI) scores and lowered their cholesterol levels.
Surprisingly, stool samples collected at the end of the study showed abundance Bifidobacteraceae. These gut microbes produce an active form of GABA; Thus, it is an important player in the stress/anxiety/sleep axis.
MetS is a well-recognized marker of dyslipidemia, hypertension, central obesity, impaired insulin sensitivity, and low-grade systemic inflammation and microbial dysbiosis in MetS.
In addition, MetS patients exhibit a deficiency in short-chain fatty acids (SCFA) that make up the gut microbiome.
Some of the studies included in this review suggested that the metabolic abnormalities observed in MetS were due to decreased bacterial deconjugation activity of primary bile acids.
Other studies have shown that microbial-derived metabolites called branched-chain aromatic amino acids (BCAAs), such as leucine, were involved in obesity-related insulin resistance through an mTOR-dependent mechanism.
More and more studies have noted the importance of timing and rhythm of feeding in shaping the gut microbiota communities that it can achieve.
Thus, only long-term dietary intervention can permanently alter the gut microbial composition to improve MetS.
Furthermore, multiple animal studies and studies with human subjects have demonstrated that higher intake of dietary fiber leads to a higher prevalence of SCFA producers in the gut bacteria, which is beneficial for glucose homeostasis and improves metabolic parameters in MetS.
Importantly, this effect correlates with its richness Bifidobacterium Improvement in sleep is observed.
Overall, this review highlights the importance of fiber-rich foods in modulating beneficial bacteria in the gut microbiota composition of individuals with MetS and sleep disorders.
In sleep disorders, a potentially common microbial signature is reduced abundance of butyrate (an SCFA) producers, especially Faecalibacterium prasnitzii, Along with this some members have been reduced Lachnospiraceae family, like Roseburiaand a prosperity Bacteridates phylum
This pattern is similar to the observed reduction of SCFA producers in MetS. Because the MetS cohorts examined in this review were larger, more controlled, and better taxonomically defined, their microbial patterns are more consistent for further investigation.