In a recently published article in International Journal of Molecular SciencesScientists describe the importance of the gut-brain-microbiota axis in establishing optimal mental health in adulthood (18-25 years).
Research: Drugs, guts, brains, but not rock’n’roll: The need to consider the role of the intestinal microbiota in modern mental health and well-being of emerging adults. Image Credit: Alpha Tauri 3D Graphics
Adulthood is a critical period for the development of neurons, neuroplasticity and maturation of the hypothalamic-pituitary-adrenal axis. During this period, stress reactions, including fluctuations in hormone levels and varied activation of the hypothalamic-pituitary-adrenal axis, have a significant impact on the development of mental health. Studies show that mental illness often occurs in new adults during this period.
The intestinal microbiota is a collection of different microorganisms, including bacteria that reside in the gastrointestinal tract. Various factors, including genetic factors, early life factors (maternal infection, antibiotic use, etc.) and environmental / lifestyle factors (diet, physical activity, stress, etc.), can significantly change the composition and the diversity of the intestinal microbiota.
Recent evidence suggests that emerging adulthood is associated with a unique vulnerability in the intestinal microbiota. In emerging adults, the intestinal microbiota is less diverse, simple, and more unstable than in children, adolescents, and the elderly. In the present article, researchers have suggested that the gut-brain-microbiota axis may play a role in identifying mental health problems that are significantly increasing in Western countries, most likely due to unfavorable lifestyle behaviors.
The interface between intestinal microbiota and mental health probably depends on several factors. (A) The first is the entrances to the intestinal tract, which form the microbiota (diet, drugs, antimicrobials, etc.). (B) Periods in which the microbiota undergoes changes in diversity (alpha) occur in healthy people, especially between late teens and early twenties, which probably leads to differences in metabolic production that affect brain health. (° C) The intersection of the adolescent’s brain combined with the normally variable age microbiota, the promotion of the desired microbiota through physical activity / exercise and circadian rhythm, and the less desirable microbiota using different substances. part (° C) adapted by Bian et al., 2017. Figure created with Biorender (available April 29, 2022).
The gut-brain-microbiota axis
Intestinal microorganisms produce several vital components, such as short-chain fatty acids, neurotrophic factors derived from the brain, and neurotransmitters that mediate gut-brain communication. Imbalance in the intestinal 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.
Influence of the intestinal microbiota on mental health
According to the available literature, there is a link between the intestinal microbiota and mental health. In this context, studies have shown that antibiotic-induced changes in the intestinal microbiota are associated with altered emotional behavior. The gut-brain-microbiota axis is known to play a significant 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 intestinal microbiota during adulthood can cause a cascade of events that have a lasting negative impact on both physical and mental health.
Impact of environmental / lifestyle factors on intestinal microbiota and mental health
Environmental factors that have the greatest impact on the formation of the intestinal microbiota include diet, drugs and antimicrobials. In addition, physical activity, sleep patterns and substance use significantly affect the intestinal microbiota as well as mental health.
General findings on different types of diet on the gut-brain-microbiome axis. (A) Diets rich in vegetables, fiber, trace elements such as vitamins D and C, probiotics and prebiotics, fermented foods, anti-inflammatory rich in omega-3, low-fat and low-carbohydrate foods promote positive mental health and increase Bacteroidetes, Prevotella, Bifodobacteria, Akkermansia, Roseburia, Lactilobacillus, and interleukin (IL) -10, and decreased in Firmicutes, Escherichia coli, Ruminococcus, Coprococcus, vascular endothelial protein growth factor-1, international endothelial growth factor gamma-induced protein 10 17, IL-12, c-reactive protein, IL-2, tumor necrosis factor and lipopolysaccharide. (B) Foods high in fat, high in sugar and over-processed foods increase the amount of bacteria, bile acids, Bilophila wadsworth, Enterobacteriaceae, Firmicutes, Enterobacteriaceae, Escherichia, Klebsiella and Shigella. Figure created with Biorender (available April 29, 2022).
Dietary components significantly affect the composition and diversity of the intestinal microbiota. Excessive consumption of unhealthy foods (saturated fats, refined sugar, red meat and low-fiber foods) and lower consumption of healthy foods (fruits and vegetables) can cause microbial dysbiosis, which is characterized by changes in functional composition, the diversity, local distribution and metabolic activities of the intestinal microbiota.
Strong evidence suggests that a diet rich in vegetables, fruits, fiber, fermented foods, vitamins, probiotics and polyunsaturated fatty acids helps maintain homeostasis of the intestinal microbiota and promotes positive mental health. In contrast, foods high in fat, high in carbohydrates and over-processed are associated with intestinal dysbiosis, inflammation and poor mental health.
It is well known that regular physical activity is vital for maintaining metabolic and cardiovascular fitness and improving mental health. In addition, with regard to intestinal microbial diversity, it is known that physical activity increases 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 eating habits. In particular, intense physical activity can cause dysbiosis and inflammation of the intestinal microbiosis and cause adverse health effects. Therefore, the optimal level of physical activity must be individualized.
Use of substances
Excessive consumption of nicotine, alcohol, cannabis and illicit substances is often observed in emerging adults, especially those living in Western countries. These substances are known to have negative effects on both physical and mental health.
Neurotic nicotinic acetylcholine receptors are vital for the development and maturation of the central nervous system. Nicotine consumption at an early age can lead to addiction, cognitive decline and psychiatric disorders. In addition, nicotine consumption can cause an imbalance of the intestinal microbiota by increasing the permeability of the intestinal mucosa and disrupting the immune responses of the mucosa.
Excessive alcohol consumption at an early age can cause changes in the frontal and temporal lobes of the brain and disrupt neural networks related to learning, memory, psychomotor speed, attention, performance and impulsivity. In the gut, alcohol alters metabolic levels, increases inflammation and disrupts the integrity of the intestinal epithelium.
Cannabis consumption increases cannabinoid receptor activity and causes a variety of health outcomes, including induction of gastric acid secretion, decreased intestinal motility, and induction of intestinal permeability and inflammation. In addition, studies show that cannabis use in early life is associated with reduced cognitive abilities.
Regular sleep patterns can be affected by certain factors, including shift work, exposure to light at night, inconsistent mealtimes, unhealthy eating, and aircraft delays. Changes in the timing and pattern of sleep are commonly seen among adolescents associated with mental disorders such as depression and anxiety.
Disruption of sleep patterns can also disrupt the homeostasis of the intestinal microbiome by increasing harmful microbes and reducing beneficial microbes and metabolites.
Reference in the magazine:
- Lee JE. 2022. Drugs, guts, brains, but not rock’n’roll: The need to consider the role of the intestinal microbiota in modern mental health and well-being of emerging adults. International Journal of Molecular Sciences. https://www.mdpi.com/1422-0067/23/12/6643