Positive Health Online

Probiotics are live microorganisms that are beneficial for human health when consumed in adequate amounts. They are commonly found in fermented foods such as yogurt, kefir, and sauerkraut, as well as in dietary supplements. While probiotics have been primarily studied for their benefits on digestive health, recent research suggests that they may also have a positive effect on emotions. The gut-brain axis, which connects the gut and the brain, plays a key role in regulating emotions and has been found to be influenced by the composition of the gut microbiome. This essay will review the current research on the effects of probiotics on emotions, including their potential to reduce stress, anxiety, and depression.

https://en.wikipedia.org/wiki/File:Gut-Brain_Axis.png

Schematic diagram showing the communication between the gut and brain

Picture Credit: Suganya, Kanmani, and Byung-Soo Koo on Wikipedia

Effects of Probiotics on the Gut-Brain Axis

The gut-brain axis is a complex network of communication between the gut and the brain that influences various physiological processes, including emotions. The gut is home to trillions of microorganisms that make up the gut microbiome. These microorganisms play an essential role in maintaining the health of the gut and regulating the gut-brain axis. Recent research has shown that the gut microbiome can influence brain function and behavior by producing neurotransmitters and other signaling molecules that communicate with the brain.

Probiotics can alter the composition of the gut microbiome, leading to changes in the production of neurotransmitters and signaling molecules that can affect emotions. For example, certain strains of probiotics have been shown to increase the production of gamma-aminobutyric acid (GABA), a neurotransmitter that has a calming effect on the brain. GABA helps to reduce anxiety and promote relaxation. Lactobacillus rhamnosus, a strain of probiotic, has been found to increase GABA production and reduce anxiety-like behavior in mice.

Another way that probiotics can affect emotions is by modulating the immune system. The gut microbiome plays an important role in regulating the immune system, and probiotics have been shown to influence immune function in a variety of ways. For example, certain strains of probiotics can reduce inflammation in the gut and throughout the body. Chronic inflammation has been linked to a range of mood disorders, including depression and anxiety.

Effects of Probiotics on Stress

Stress is a common experience that can have negative effects on physical and emotional health. Chronic stress has been linked to a range of health problems, including heart disease, obesity, and depression. The gut-brain axis plays a key role in regulating the stress response, and research suggests that probiotics may be effective in reducing stress levels.

Animal studies have shown that certain strains of probiotics can reduce stress levels by regulating the hypothalamic-pituitary-adrenal (HPA) axis, which controls the body's stress response. The HPA axis is activated in response to stress and leads to the release of cortisol, a stress hormone. Chronic activation of the HPA axis can lead to dysregulation of cortisol levels and contribute to the development of mood disorders. Probiotics have been shown to reduce cortisol levels and improve the HPA axis response in both animals and humans.

Evidence from Human Studies on Probiotics and Cortisol

Several human studies have explored the effects of probiotic supplementation on cortisol levels, with many demonstrating promising results. A study conducted by Messaoudi et al. (2011)[6] tested the effects of Lactobacillus helveticus and Bifidobacterium longum in healthy volunteers. The results indicated a significant reduction in cortisol levels among participants taking the probiotic formulation compared to those in the placebo group. Additionally, participants reported improvements in psychological wellbeing, suggesting that these probiotics could help alleviate stress by modulating cortisol levels.

Another study by Takada et al. (2016) investigated the effects of a probiotic strain of Lactobacillus casei on cortisol levels in medical students during an exam period, a time of increased stress. Results showed that students who consumed the probiotic had lower salivary cortisol levels compared to the placebo group, indicating a potential buffering effect of probiotics against stress-induced cortisol elevation.

A systematic review conducted by Cryan et al. (2019) examined multiple clinical trials assessing the influence of various probiotics on cortisol and stress-related outcomes. The analysis concluded that probiotics, particularly those from the Lactobacillus and Bifidobacterium genera, appear effective in reducing cortisol levels in humans, though the efficacy may vary depending on the specific strain and dosage used.

Mechanisms by Which Probiotics Influence Cortisol

The exact mechanisms by which probiotics may lower cortisol levels remain a subject of ongoing research. However, several plausible pathways have been proposed:

• Modulation of the HPA Axis: Probiotics have been shown to regulate the HPA axis, thereby impacting cortisol production. Studies suggest that certain probiotic strains can lower corticotropin-releasing hormone (CRH) levels, which in turn reduces adrenocorticotropic hormone (ACTH) release and subsequently lowers cortisol secretion;
• Production of Neurotransmitters and Metabolites: Some probiotic strains produce neurotransmitters like gamma-aminobutyric acid (GABA) and short-chain fatty acids (SCFAs), which may positively impact mood and stress responses. GABA, an inhibitory neurotransmitter, has calming effects on the CNS and may reduce the HPA axis activation.
• Reduction of Systemic Inflammation: Chronic inflammation can stimulate the HPA axis; and contribute to elevated cortisol levels. Probiotics help reduce systemic inflammation by enhancing gut barrier integrity, reducing endotoxemia, and promoting anti-inflammatory cytokine production, which may alleviate HPA axis stimulation;
• Influence on Vagus Nerve Activity: The vagus nerve is a critical component of the gut-brain axis, transmitting signals from the gut microbiota to the brain. Some probiotics have been shown to stimulate the vagus nerve, promoting relaxation responses and potentially reducing cortisol production by downregulating the HPA axis.

Effects of Probiotics on Anxiety

Anxiety is a common mental health disorder characterized by feelings of worry, nervousness, and fear. It can have a significant impact on daily life and can contribute to a range of physical and emotional health problems. Research suggests that probiotics may be effective in reducing symptoms of anxiety.

Several clinical trials have investigated the effects of probiotics on anxiety in humans. A study published in the Journal of Clinical Psychiatry found that a probiotic supplement containing Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum significantly reduced symptoms of anxiety and depression in patients with irritable bowel syndrome. Another study published in the Journal of Psychiatric Research found that a probiotic supplement containing Lactobacillus helveticus and Bifidobacterium longum reduced symptoms of anxiety and improved cognitive function in healthy volunteers.

The mechanisms by which probiotics reduce anxiety are not yet fully understood, but it is thought that they may work by regulating the production of neurotransmitters and inflammatory cytokines in the gut. A study published in Brain, Behavior, and Immunity found that a probiotic supplement containing Lactobacillus casei reduced anxiety-like behavior in mice by reducing levels of inflammatory cytokines in the gut.

Effects of Probiotics on Depression

Depression is a common mental health disorder characterized by persistent feelings of sadness, hopelessness, and loss of interest in daily activities. It can have a significant impact on quality of life and is a leading cause of disability worldwide. Research suggests that probiotics may be effective in reducing symptoms of depression.

Several clinical trials have investigated the effects of probiotics on depression in humans. A study published in the British Journal of Nutrition found that a probiotic supplement containing Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum significantly reduced symptoms of depression and anxiety in patients with major depressive disorder. Another study published in the Journal of the American Medical Association found that a probiotic supplement containing Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum reduced symptoms of depression in patients with irritable bowel syndrome.

The mechanisms by which probiotics reduce symptoms of depression are not yet fully understood, but it is thought that they may work by modulating the gut microbiome and reducing inflammation in the gut and throughout the body. A study published in the Journal of Affective Disorders found that a probiotic supplement containing Lactobacillus acidophilus, Bifidobacterium bifidum, and Streptococcus thermophilus reduced symptoms of depression in patients with major depressive disorder by reducing inflammation.

Research suggests that probiotics may have a positive effect on emotions, including reducing stress, anxiety, and depression. The gut-brain axis plays a key role in regulating emotions, and the composition of the gut microbiome can influence brain function and behavior. Probiotics can alter the composition of the gut microbiome, leading to changes in the production of neurotransmitters and signaling molecules that can affect emotions. Additionally, probiotics can modulate the immune system, reducing inflammation and stress levels.

Several clinical trials have investigated the effects of probiotics on emotions in humans, and the results are promising. However, more research is needed to fully understand the mechanisms by which probiotics exert their effects on emotions and to identify the most effective strains and doses of probiotics for specific emotional disorders.

These studies provide evidence that probiotics can have a positive effect on emotional well-being and mental health. Some of the mechanisms proposed for these effects include the modulation of the HPA axis, regulation of neurotransmitters such as GABA, and the improvement of gut-brain communication through the microbiota-gut-brain axis. While more research is needed to fully understand the complex relationship between probiotics and emotions, the existing evidence suggests that probiotic supplementation may be a promising approach for managing symptoms of anxiety, depression, and stress.

Probiotics present a promising, natural approach to reducing cortisol levels and managing stress, with potential benefits for mental health and overall wellbeing. By influencing the gut-brain axis and modulating the HPA axis, probiotics can play a role in balancing cortisol production, enhancing resilience to stress, and potentially alleviating symptoms associated with anxiety and depression. However, the effects of probiotics on cortisol are complex and appear to be strain-specific, dosage-dependent, and subject to individual variation.

Further research is necessary to fully understand the therapeutic potential of probiotics in cortisol regulation and to establish evidence-based guidelines for their use in stress management. The growing body of evidence suggests that probiotics may one day serve as an important tool in the holistic management of stress and its physiological effects, offering a promising avenue for individuals seeking to improve their health naturally.

Further Reading

1. Bravo, J. A., Forsythe, P., Chew, M. V., Escaravage, E., Savignac, H. M., Dinan, T. G., ... & Cryan, J. F. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences, 108(38), 16050-16055. 2011.
2. Berk, M., Williams, L. J., Jacka, F. N., O'Neil, A., Pasco, J. A., Moylan, S., & Maes, M. So depression is an inflammatory disease, but where does the inflammation come from? BMC medicine. 2013.
3. Mohammadi, A. A., Jazayeri, S., Khosravi-Darani, K., Solati, Z., Mohammadpour, N., Asemi, Z., ... & Adab, Z. The effects of probiotics on mental health and hypothalamic-pituitary-adrenal axis: A randomized, double-blind, placebo-controlled trial in petrochemical workers. Nutritional neuroscience, 19(9), 387-395. 2016.
4. Allen, A. P., Hutch, W., Borre, Y. E., Kennedy, P. J., Temko, A., Boylan, G., ... & Clarke, G. Bifidobacterium longum 1714 as a translational psychobiotic: modulation of stress, electrophysiology and neurocognition in healthy volunteers. Translational psychiatry, 6(11), e939-e939. 2016.
5. Pinto-Sanchez, M. I., Hall, G. B., Ghajar, K., Nardelli, A., Bolino, C., Lau, J. T., ... & Bercik, P. Probiotic Bifidobacterium longum NCC3001 reduces depression scores and alters brain activity: a pilot study in patients with irritable bowel syndrome. Gastroenterology, 153(2), 448-459. 2017.
6. Messaoudi, M., Violle, N., Bisson, J. F., Desor, D., Javelot, H., & Rougeot, C. Beneficial psychological effects of a probiotic formulation (Lactobacillus helveticus and Bifidobacterium longum) in healthy human volunteers. Gut microbes, 2(4), 256-261. 2011.
7. Bravo, J. A., Forsythe, P., Chew, M. V., Escaravage, E., Savignac, H. M., Dinan, T. G., ... & Cryan, J. F. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences, 108(38), 16050-16055. 2011.
8. Kazemi, A., Noorbala, A. A., Azam, K., Eskandari, M. H., Djafarian, K., & Shab-Bidar, S. The effect of probiotic and/or prebiotic on markers of psychological stress in adults with major depressive disorder: A systematic review and meta-analysis of randomized controlled trials. Nutritional neuroscience, 21(7), 455-465. 2018.
9. Pinto-Sanchez, M. I., Hall, G. B., Ghajar, K., Nardelli, A., Bolino, C., Lau, J. T., ... & Bercik, P. Probiotic Bifidobacterium longum reduces depression scores and alters brain activity: a pilot study in patients with irritable bowel syndrome. Gastroenterology, 153(2), 448-459. 2017.
10. Akkasheh, G., Kashani-Poor, Z., Tajabadi-Ebrahimi, M., Jafari, P., Akbari, H., Taghizadeh, M., ... & Esmaillzadeh, A. Clinical and metabolic response to probiotic supplementation in patients with major depressive disorder: A randomized, double-blind, placebo-controlled trial. Nutrition, 32(3), 315-320. 2016.
11. Davari, S., Talaei, S. A., Alaei, H., & Salami, M. Probiotics treatment improves diabetes-induced impairment of synaptic activity and cognitive function: behavioral and electrophysiological proofs for microbiome-gut-brain axis. Neuroscience, 240, 287-296.
12. Huang, R., Wang, K., & Hu, J. Effect of probiotics on depression: a systematic review and meta-analysis of randomized controlled trials. Nutrients, 8(8), 483. 2013. 2016.
13. Pirbaglou, M., Katz, J., de Souza, R. J., Stearns, J. C., Motamed, M., Ritvo, P., & Brown, K. Probiotic supplementation can positively affect anxiety and depressive symptoms: a systematic review of randomized controlled trials. Nutrition research, 36(9), 889-898. 2016.
14. Wang, H. X., & Wang, Y. P. (2016). Gut microbiota-brain axis. Chinese medical journal, 129(19), 2373. 2016.
15. Lee, H. J., & Lee, K. E. Probiotics in human health and disease: from nutribiotics to pharmabiotics. Journal of microbial and biochemical technology, 10(2), 1-5. 2018.
16. Naseribafrouei, A., Hestad, K., Avershina, E., Sekelja, M., Linløkken, A., Wilson, R., ... & Rudi, K. Correlation between the human fecal microbiota and depression. Neurogastroenterology & Motility, 26(8), 1155-1162. 2014.
17. Dinan, T. G., Stanton, C., Cryan, J. F. Psychobiotics: A novel class of psychotropic. Biological Psychiatry, 74(10), 720-726. 2013.