Globally, mental health disorders have become a public health concern as they are the leading source of disability. Therefore, mental health needs a new approach to intervention and treatment. However, it has been hard to prevent or treat mental health when the healthcare practitioner does not know its primary cause. The psychiatric diagnostic manuals on mental health have changed over time, preventing the understanding of what the condition constitutes. In the contemporary world, neuro-explanation of mental illness has dominated research, with the issue being re-cast as brain or neuro conditions which have resulted in more studies on the gut-brain axis. The human gastrointestinal tract shields numerous microorganisms referred to as gut microbiota. Gut microbiota constitutes primarily bacterial but can also include fungi, viruses, archaea, and protozoa. Recent studies have proven that in the human gut, the number of bacteria exceeds that of human cells. Therefore, given its adverse genetic perspective, microbiota plays a significant role in almost all mental processes in the human body. When humans are exposed to stress, their bodies undergo a series of energy modifications, and multiple signals are diverted to the brain and muscles. Also, pressure can release cortisol, and all these components impact the gut microbiome. Correspondingly, the gut microbiota imbalance can lead to overall human mood alterations. The rationale is that gut bacteria activity imbalance affects anxiety, depression, and stress leading to mental health disorders.
The Gut infection
Bacteria in the human gut can either help prevent mental health such as depression, stress, and anxiety or they can make them worse. Similarly, according to Wallace and Milev (2017), mental disorders connect to the gut microbiome. Microbiomes are all the microorganisms in the human gut. Wallace and Milev (2017) posit that there are about one hundred trillion microorganisms in the human gut that establishes and maintains the intestinal lining. The colon, which essentially contains these microorganisms, directly connects to the brain and is also responsible for letting nutrients into the human body. The microbiome is influenced by numerous factors like age, diet, genetics, sex, and stress (Wallace & Milev, 2017). Recent studies have connected colon bacteria to depression and anxiety (Wallace & Milev, 2017). According to Wallace and Milev (2017), there is enough data to suggest that mental stress increases gastrointestinal lining permeability, meaning the microbiome can modulate and affect emotional behavior. In this regard, the colon wall is predominantly pertinent, emphasizing microbiota, intestinal permeability, and the immune response. Ait-Belgnaoui et al. (2012) allude that healthcare practitioners and researchers have reported inflammatory bowel and irritable bowel syndrome in colon epithelial barrier damage due to adverse intestinal permeability.
The aforementioned permeability can also lead to anxiety and depression. According to Ait-Belgnaoui et al. (2012), stressful life events can contribute to brain-gut cross-talk in diseases caused by digestion, leading to anxiety disorders. When the human body experiences stress, it shuts down unimportant activities and directs its energy and resources to the brain, thus causing microbiome imbalance (Wallace & Milev, 2017). Even if the brain and the microbiota cross-talk are weak, bacteria produce butyrate or benzodiazepine ligands with antidepressant influence (Ait-Belgnaoui et al., 2012). However, adverse conditions of inflammation and chronic stress lead to imbalanced microbiota. According to Ait-Belgnaoui et al. (2012), the bacteria imbalance leads to bacteria-derived substance manufacturing which alters the colon wall function. The imbalance also alters brain function, which leads to more anxiety. Research by Ait-Belgnaouri et al. (2012) found that gut bacteria can interact with the CNS or the central nervous system, resulting in brain neurochemistry and behavioral modifications. Further, the study subjected mice to campylobacter jejuni and citrobacterium rodentium and found that it increased anxiety-like behavior. Ait-Belgnaouri et al. (2012) allude that the rationale is that since mice not subjected to any sicknesses were anxiety free, there is a brain and bacteria cross-talk that can be extended over pathogens.
Another connection to gut infection lies in the gut-brain axis or the CNS since the two have extensive bidirectional communication. Bonaz et al. (2018) articulate that this bidirectional communication between the gut, the brain, and the microbiota involves the autonomic nervous system. However, researchers have found that bacteria convey messages to the brain through the vagus nerve or the VN. According to Bonaz et al. (2018), VN, which is the main element of the parasympathetic CNS, has 80% and 20% mixed nerves composed of afferent and efferent fibers, respectively. Thus, due to its interceptive awareness role, through its afferents, it can sense the microbiota metabolites and transfer data from the gut to the CNS, generating either an adaptive or a lousy response through the central automatic network. According to Bonaz et al. (2018), an inflammatory pathway inhibits peripheral tenderness through the VN’s fiber and reduces the colon’s permeability. Additionally, stress also inhibits the VN. Bonaz et al. (2018) posit that this inhibition involves the pathophysiology of gastrointestinal illnesses and has deleterious impacts on the microbiota and the gastrointestinal tract. The sympathetic NS is stimulated by stress which dampens VN.
As aforementioned, numerous bacteria are found in the colon. Healthy individuals have two bacterial phyla, the firmicutes, and the Bacteroides, which take over the composition (Bonaz et al., 2018). However, the bacteria release compounds like γ-aminobutyric acid, which can fundamentally act on the NS locally. When these released elements through the circumventricular organs and the blood reach the big brain via the vagus nerve, according to Bonaz et al. (2018), vagal afferent fibers do not have direct interactions with the gut luminal microbiota, but they can sense signals. When these signals are sent to the brain, humans can alter their behavior leading to stress depending on the kind of communication received. According to Bonaz et al. (2018), stress influence on the GI tract is eminent. When stress moves through its related peptide urocortin and corticotrophin-releasing factor, CRF, into the brain, it increases modified gut microbiota and colon permeability. Bonaz et al. (2018) allude that CRF proliferates colonic permeability through mast cell discharge of tumor necrosis factor. Further, chronic early stress leads to anxiety and depression. A study by Ait-Belgnaoui et al. (2012) found that mice infected by citrobacterium rodentium, an immunological stimulus stronger than stress, had anxiety behavior in the first exposure phase. The rationale is that if the human brain is experiencing stress or a powerful stimulus, the human is bound to be anxious.
Similarly, dysbiosis through alteration of colonic permeability due to chronic early stress in rats results in visceral hypersensitivity. According to Bonaz et al. (2018), naturally, stress constraints VN, and through the autonomic neurons, it kindles the sympathetic nervous system. However, as well-known, VN has afferent and efferent fibers; thus, it contains anti-inflammatory properties. In this regard, stress has pro-inflammatory properties, and so is depression and anxiety (Bonaz et al., 2018). A long-term pro-inflammatory cytokine is exposed through severe stress exposure. Thus, according to Bonaz et al. (2018), during the recovery time, it agrees with the parasympathetic rebound. Further, stress could counter the vagus nerve’s widespread impact on the epithelial wall and disrupt epithelial homeostasis, thus favoring dysbiosis (Bonaz et al., 2018). Nonetheless, according to Lew et al. (2019), stress is an event trigger, while anxiety results from that stress; thus, if not treated, it can lead to psychotic conditions like depression. In the world, three hundred million individuals with depression, out of which 800000 die due to suicide in a year (Lew et al., 2019). The article further articulates that long-term prolonged glucocorticoid levels caused by stress negatively influence immunological conditions (Lew et al., 2019). Additionally, it modifies the hippocampal structure, resulting in neuronal morphology variations, neurogenesis, and sometimes cell demise.
Notably, aside from anxiety, gut health can also lead to depression. According to Wallace and Milev (2017), psychiatric disorders of unknown etiology are major depressive disorder, MDD. At some point in life, MDD affects 20% of the population; thus, it is the leading disability globally (Wallace & Milev, 2017). MDD is featured as loss of interest, sleep and appetite alterations, low mood, hopelessness, and feeling of guilt. Wallace and Milev (2017) allude that MDD disrupts human’s daily functioning, employment, relationships, and school performance. However, MDD is connected to gut health. According to Wallace and Milev (2017), individuals with depression have amplified manifestations of interferon, pro-inflammatory cytokines, and CRP. Overall, there is an intensification in swelling, which results in depression by stimulating the HPA axis. According to Wallace and Milev (2017), the activation also triggers and alters metabolism and the availability of neurotransmitter precursors. However, the inflammation which results in depression is due to increased colonic permeability, commonly known as leaky gut in humans. Toxins are allowed into the human body when the intestinal is permeable. According to Wallace and Milev (2017), the gastrointestinal lining’s tight junction gets damaged, or the permeability worsens, and waste and toxins leak into the bloodstream.
The Gut and the Brain
Individuals suffering from depression have significant anxiety, mood, and cognitive symptoms. However, in recent years, the gut and brain connection has been associated with aforestated mental health conditions. According to Wallace and Milev (2017), there is a bidirectional way of conveying messages between the GI tract and the CNS, commonly known as the gut-brain axis. The article further suggests that the realm of psychological disorder treatment is like the gut-brain axis due to its connection to the GI tract (Wallace & Milev, 2017). For instance, irritable bowel syndrome and inflammatory bowel diseases are due to increased gut permeability. Due to the gut-brain axis interaction, these diseases can cause an individual to have anxiety and depression. According to Wallace and Milev (2017), psychologists have associated mental disorders with microbiome modification. Researchers have revealed a direct and extensive biochemical signaling of the GIT and the CNS in the last decade. According to Barbaro et al. (2018), this is why the gut-brain axis or the CNS has been connected to psychotic conditions.
How gut infection affects digestion
Good digestion is a very crucial aspect when it comes to gut health. To digest, we need to be in a parasympathetic, or “rest and digest” state (Bonaz et al., 2018). The primary element of the parasympathetic NS is the vagus nerve, which as aforestated, is a mixture of the efferent and afferent nerves (Bonaz et al., 2018). According to Bonaz et al. (2018), the VN is considered the sixth sense. Thus, in the case of microbiota in the digestive tract, the VN senses then and transfers this gut data from the tract to the central nervous system. According to Bonaz et al. (2018), this gut information is integrated to give a response, which could result in neurodegenerative disorders or disseminate an uncontrolled digestive tract disorder. Bonaz et al. (2018) articulate that if the human body is not relaxed, it cannot make up that gastric juice that destroys everything you ingest.
When this happens, the body cannot absorb food that might help, such as nutrients, vitamins, and minerals that humans need to support a healthy body and brain. Without a healthy mind, the body gets stressed, which leads to mental issues like anxiety and depression. According to Barbaro et al. (2018), patients with GI symptoms and non-celiac gluten sensitivity, NCGS, who cannot concentrate, have reduced mnemonic capabilities, anxiety, numbness, and drowsiness. NCGS is a disorder that has an extra-colonic and intestinal connection to gluten-containing food ingestion (Barbaro et al., 2018). After an individual ingests gluten, it is hydrolyzed by gastrointestinal tract proteases, which leads to inadequate digestion of gluten due to the abundance of proline and glutamine (Barbaro et al., 2018). Studies have indicated gut permeability due to the aforementioned gluten problem (Barbaro et al., 2018). As discussed earlier, gut permeability makes the body stressed, which leads to anxiety and depression. For instance, Lew et al. (2019), alleviating stress leads to depression, anxiety, and cognitive and memory disorders.
Treatment
Although gut infections lead to depression and anxiety, treating gut infections can improve these mental health symptoms. Thus, co-occurring mental illnesses must be treated directly using specific treatments. For instance, using probiotics, nutrition, and increasing serotonin has been a significant help in alleviating. According to Lew et al. (2019), probiotics are living microorganisms that help maintain the host’s health if utilized by the body. One commonly administered probiotic is Lactobacillus, which exerts homeostasis and gut health (Lew et al., 2019). Probiotics function by modulating human activities and behaviors that are stressed. Lew et al. (2019) posit that probiotics-based products put more emphasis on brain health due to the gut-brain axis relationship and the fact that it is what gets affected by mental health disorders. During research by the same article, researchers utilized L. Plantarum P8 probiotic strain with gut exert effects against mental health diseases like depression. According to Lew et al. (2019), currently, depression is being treated by focusing on neurotransmitter brain activity, but the side effects are serious such as headaches, sedation, nausea, and agitation.
Another alternative treatment for these mental disorders is nutritional psychiatry. The nutritional psychiatry field explores mental health disorders and dietary patterns (Wallace& Milev, 2019). Wallace and Milev (2019) further articulate that the brain’s function and organization depend on nutrient intakes such as minerals, fats, amino acids, and minerals. Thus, healthcare practitioners must check and change their patients’ diets to regulate mental health.
Admittedly, toxins in the bloodstream are commonly known as gut-derived endotoxins or LPS lipopolysaccharides. Wallace and Milev (2017), LPS are fragments in the gram-negative bacteria’s external membrane and can cause depression. On the other hand, serotonin is a monoamine neurotransmitter associated with MDD’s pathogenesis and pathophysiology. According to Wallace and Milev (2017), the connection’s main target is SSRIs. Serotonin biosynthesized from the vital amino acid tryptophan in GIT and the CNS. In the CNS, serotonin regulates emotions, appetite, sleep, and stress (Wallace & Milev, 2017). However, Wallace and Milev (2017) posit that serotonin in the GIT helps in intestinal secretions and motility. Modifications in the microbiome overwhelmingly stimulate serotonin’s neurotransmission in CNS and the peripheral. Notably, research has hypothesized that if probiotics were to be used in the treatment of depression in the GIT, it would improve the CNS-associated symptoms by boosting the free manufacturing of tryptophan, which in turn increases the availability of serotonin (Wallace & Milev, 2017). According to Wallace and Milev (201), serotonin availability facilitates the regulation of the HPA axis and decreases symptoms of depression caused by neurotransmitter depletion.
However, when utilizing probiotics to treat anxiety and depression, the healthcare practitioner must understand that there are numerous strains. According to Wallace and Milev (2017), probiotics are of different species strains found in different food supplements; thus, their health benefit effect is species- and strain-specific. Wallace and Milev (2017) articulate that the most beneficial ones are Bifidobacterium and Lactobacillus, as they have been studied concerning psychological disorders. Other species, like Bacillus and Streptococcus, can be utilized for mental health but do not show any effects. Nevertheless, the most effective combination or strain has not been identified. According to Wallace and Milev (2017), B. longum and L. helveticusimpact the gut-brain axis in treating mental health. However, none of the studies have used a single strain to illustrate their effectiveness. The study recommends further research on the strains to determine the most efficacious one in treating mental health, especially anxiety and depression disorders. The research should be an RCT to give the cause-effect outcome on the intervention of depression and anxiety disorders.
Conclusion
The brain, microbiome, and gut have a bidirectional connection which researchers have studied in the contemporary world due to increasing mental health cases. The study has demonstrated the link between the three brings about depression and anxiety. Similarly, the research has demonstrated the significance of a healthy microbiome, especially the gut microbiota, for individuals with depression and anxiety. Additionally, the study has evaluated that dysbiosis and inflammation are linked to mental health disorders in the CNS. Also, due to gut permeability, a human can experience pain which triggers the brain to be stressed, leading to anxiety and depression. Poor digestion is another issue that has been linked to mental health disorders. However, probiotics, nutrition, and increasing serotonin can help treat the aforementioned mental disorders. For instance, improving diet, increasing serotonin, and ingesting the microorganisms called probiotics can exert gut health. However, when a physician chooses the probiotics intervention technique, they should be vigilant as not all strains work. So far, the only combination of strains that work is Bifidobacterium and Lactobacillus. Thus, further research is needed to determine the most influential single probiotic strain.
References
Ait-Belgnaoui, A., Durand, H., Cartier, C., Chaumaz, G., Eutamene, H., Ferrier, L., Theodorou, V. (2012). Prevention of gut leakiness by a probiotic treatment leads to attenuated HPA response to acute psychological stress in rats. Psychoneuroendocrinology,37(11), 1885-1895. doi:10.1016/j.psyneuen.2012.03.024
The study will use the above source to discuss the microbiome and its effect on numerous Central Nervous System disorders such as anxiety, depressive disorders, schizophrenia, and autism. The article will also help discuss the human gut and the brain and how they may cause anxiety and depressive disorders.
For instance, the study will focus on the impression of the function of the gut microbiome, from its development to its relationship with the emotional and cognitive centers of the brain.
Barbaro, M. R., Cremon, C., Stanghellini, V., & Barbara, G. (2018). Recent advances in understanding non-celiac gluten sensitivity. F1000Research,7, 1631. doi:10.12688/f1000research.15849.1
The research will rely on the above source to obtain data on digestion and gut health. In order to digest, we need to be in a parasympathetic, or “rest and digest,” state.
Bonaz, B., Bazin, T., & Pellissier, S. (2018). The vagus nerve is at the interface of the microbiota-gut-brain axis. Frontiers in Neuroscience,12. doi:10.3389/fnins.2018.00049.
The research will utilize the above article to retrieve data on the brain, the microbiota, and the gut, to understand how the three communicate through the microbiota-gut-brain axis. The source will provide information on gut and mental health disorders like depression and anxiety. The source will also provide information on the vegas nerve and the digestive tract. Additionally, it will provide data on the parasympathetic nervous system.
Lew, L., Hor, Y., Yusoff, N. A., Choi, S., Yusoff, M. S., Roslan, N. S., Liong, M. (2019). Probiotic lactobacillus Plantarum p8 alleviated stress and anxiety while enhancing memory and cognition in stressed adults: A randomized, double-blind, placebo-controlled study. Clinical Nutrition,38(5), 2053-2064. doi:10.1016/j.clnu.2018.09.010.
The study will use the above article to gain data on mental health treatment, especially the effects of probiotics on the targeted population.
Wallace, C. J., & Milev, R. (2017). The effects of probiotics on depressive symptoms in humans: A systematic review. Annals of General Psychiatry,16(1). doi:10.1186/s12991-017-0138-2
The study will utilize the above article to articulate the relationship between bacteria and health in the colon. For instance, depending on the relationship, there is a negative or positive effect on mood, anxiety levels, stress resilience, and depression.
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