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In a recently published journal article International Journal of Molecular Sciencesscientists have described the importance of the gut-brain-microbiota axis in establishing optimal mental health during adulthood (ages 18–25).

Study: Study: Drugs, guts, brains, but not rock and roll: the need to consider the role of the gut microbiota in today’s mental health and well-being of young people. Image Credit: Alpha Tauri 3D Graphics

Background

The onset of adulthood is a critical period for neuronal development, neuroplasticity, and maturation of the hypothalamic-pituitary-adrenal axis. During this period, stress reactions, including hormonal fluctuations and diverse activation of the hypothalamic-pituitary-adrenal axis, significantly affect the development of mental health. Studies have shown that mental illness often occurs in young people during this period.

The gut microbiota is a collection of diverse microorganisms, including bacteria that live in the gastrointestinal tract. Various factors, including genetic factors, early age factors (maternal infection, use of antibiotics, etc.) and environmental/lifestyle factors (diet, physical activity, stress, etc.), can seriously alter the composition and diversity of the intestinal microbiota.

Recent evidence indicates that aging is associated with a unique vulnerability of the gut microbiota. In young adults, the gut microbiota is less diverse, simpler, and more unstable than in children, adolescents, and the elderly. In the present article, scientists hypothesize that the gut-brain-microbiota axis may play a role in determining the mental health problems that are on the rise in Western countries, most likely due to unfavorable lifestyles.

The link between the gut microbiota and mental health likely depends on several factors.  (A) First, it is the intestinal tract entrances that shape the microbiota accordingly (diet, drugs, antimicrobials, etc.).  (B) Periods when the microbiota undergoes changes in diversity (alpha) occur in healthy individuals, especially between late teens and early twenties, likely leading to differences in metabolic emissions that affect brain health.  (C) Intersection of the adolescent brain coupled with typically fluctuating age group microbiota, promoting desired microbiota through physical activity/exercise and circadian rhythm and less desirable microbiota using various substances.  Part (C) adapted from Bian et al., 2017. Figure created with Biorender (accessed April 29, 2022).The link between the gut microbiota and mental health likely depends on several factors. (BUT) Firstly, these are the entrances to the intestinal tract, which shape the microbiota accordingly (diet, drugs, antimicrobials, etc.). (B) Periods when the microbiota undergoes changes in diversity (alpha) occur in healthy individuals, especially between the late teens and early 20s, likely leading to differences in metabolic emissions that affect brain health. (FROM) Intersecting the adolescent brain in conjunction with the typically fluctuating age group microbiota, promoting desirable microbiota through physical activity/exercise and circadian rhythm and less desirable microbiota through the use of various substances. Part (FROM) adapted from Bian et al., 2017. Figure created with Biorender (accessed 29 April 2022).

Gut-brain-microbiota axis

The micro-organisms that live in the gut produce several vital components such as short-chain fatty acids, brain-derived neurotrophic factors, and neurotransmitters that provide communication between the gut and the brain. An imbalance in the gut microbiota can lead to microbial lipopolysaccharide (LPS)-mediated production of inflammatory cytokines, which subsequently affect the hypothalamic-pituitary-adrenal axis by stimulating the afferent vagus nerve.

Impact of the gut microbiota on mental health

According to the available literature, there is a link between the gut microbiota and mental health. In this context, studies have shown that antibiotic-induced alteration of the gut microbiota is associated with altered emotional behavior. The gut-brain-microbiota axis is known to play an important role in the development of various neurological and psychiatric diseases, including Alzheimer’s disease, Parkinson’s disease, and autism spectrum disorder. Any imbalance in the gut microbiota during adolescence can trigger a cascade of events that have long-term negative effects on both physical and mental health.

Impact of Environmental/Lifestyle Factors on the Gut Microbiota and Mental Health

Environmental factors that have the greatest influence on the formation of the gut microbiota include diet, medications, and antimicrobial agents. In addition, physical activity, sleep patterns, and substance use significantly affect the gut microbiota as well as mental health.

Overall results for different diet types on the gut-brain-microbiome axis.  (A) A diet rich in vegetables, fiber, micronutrients such as vitamins D and C, probiotics and prebiotics, fermented foods, anti-inflammatory foods rich in omega-3s, low fat and low carbohydrates promotes positive mental health and an increase in Bacteroidetes, Prevotella, short chain fatty acids, Bifodobacteria, Akkermansia, Roseburia, Lactilobacillus and interleukin (IL)-10, decrease in Firmicutes, Escherichia coli, Ruminococcus, Coprococcus, vascular endothelial growth factor, monocyte chemoattractant protein-1, interferon gamma-induced protein 10, IL-17 , IL-12, c-reactive protein, IL-2, tumor necrosis factor and lipopolysaccharide.  (B) Foods high in fat, sugar, and ultra-processed foods increase Bacteroides, bile acids, Bilophila wadsworth, Enterobacteriaceae, Firmicutes, Enterobacteriaceae, Escherichia, Klebsiella, and Shigella.  Drawing created with Biorender (as of April 29, 2022).Overall results for different diet types on the gut-brain-microbiome axis. (A) A diet rich in vegetables, fiber, micronutrients such as vitamins D and C, probiotics and prebiotics, fermented foods, anti-inflammatory foods rich in omega-3s, low fat and low carbohydrates promotes positive mental health and an increase in Bacteroidetes, Prevotella, short chain fatty acids, Bifodobacteria, Akkermansia, Roseburia, Lactilobacillus and interleukin (IL)-10, decrease in Firmicutes, Escherichia coli, Ruminococcus, Coprococcus, vascular endothelial growth factor, monocyte chemoattractant protein-1, interferon gamma-induced protein 10, IL-17 , IL-12, c-reactive protein, IL-2, tumor necrosis factor and lipopolysaccharide. (B) Foods high in fat, sugar, and ultra-processed foods increase Bacteroides, bile acids, Bilophila wadsworth, Enterobacteriaceae, Firmicutes, Enterobacteriaceae, Escherichia, Klebsiella, and Shigella. Drawing created with Biorender (as of April 29, 2022).

Diet

Dietary components significantly influence the composition and diversity of the intestinal microbiota. Excessive intake of unhealthy foods (saturated fats, refined sugars, red meat, and low fiber foods) and reduced intake of healthy foods (fruits and vegetables) can cause microbial dysbiosis characterized by altered functional composition, diversity, and local distribution. and metabolic activity of the intestinal microbiota.

Compelling evidence indicates that a diet rich in vegetables, fruits, fiber, fermented foods, vitamins, probiotics, and polyunsaturated fatty acids helps maintain gut microbiota homeostasis and promotes positive mental health. In contrast, foods high in fat, carbohydrates, and ultra-processed foods are associated with gut dysbiosis, inflammation, and poor mental health.

Physical activity

It is well known that regular physical activity is vital for maintaining metabolic and cardiovascular health, as well as improving mental health. In addition, with regard to gut microbial diversity, physical activity is known to increase the levels of beneficial microbes and metabolites in the gut.

The impact of physical activity can vary from person to person depending on age, gender, genetic makeup, body mass index (BMI) and dietary habits. Notably, intense physical activity can cause dysbiosis and inflammation of the gut microbiota and cause adverse health outcomes. Thus, the optimal level of physical activity must be individualized.

Substance use

Excessive consumption of nicotine, alcohol, cannabis, and illegal substances is often seen in young people, especially those living in Western countries. These substances are known to have negative effects on both physical and mental health.

Neuronal nicotinic acetylcholine receptors are vital for the development and maturation of the central nervous system. Early nicotine use can lead to addiction, cognitive decline, and psychiatric disorders. In addition, nicotine consumption may cause an imbalance in the gut microbiota by increasing intestinal mucosal permeability and disrupting mucosal immune responses.

Alcohol abuse early in life can cause changes in the frontal and temporal lobes of the brain and impair neural networks associated with learning, memory, psychomotor speed, attention, executive function, and impulsivity. In the gut, alcohol alters metabolite levels, increases inflammation, and damages the integrity of the intestinal epithelium.

Cannabis consumption increases the activity of cannabinoid receptors and causes various health effects, including induction of gastric acid secretion, decreased intestinal motility, and induction of intestinal permeability and inflammation. What’s more, research has shown that early cannabis use is associated with cognitive decline.

Sleeping mode

Certain factors can affect regular sleep patterns, including shift work, exposure to light at night, inconsistent meal times, unhealthy diets, and jet lag. Adolescents typically experience shifts in the timing and patterns of sleep associated with psychiatric disorders such as depression and anxiety.

Sleep disruption can also disrupt gut microbiome homeostasis by increasing harmful microbes and decreasing beneficial microbes and metabolites.

Link to the journal:

  • Lee J.E. 2022. Drugs, guts, brains, but not rock and roll: the need to consider the role of the gut microbiota in modern youth mental health and well-being. International Journal of Molecular Sciences. https://www.mdpi.com/1422-0067/23/12/6643

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