The Gut Brain Axis, or commonly referred to as the “GBX” is the most researched area after Gastrointestinal an Immune health within the probiotic category. Moreover, the pandemic has emphasized and brought ‘mental health’ into the mainstream and made it “top of mind” as a matter that must be dealt with both during the pandemic and post-pandemic.
The scientific research is expanding rapidly into areas of dietary supplements, and also investigating probiotic interventions in mental health conditions previously treated only with pharmaceutical drugs.
The gut has been referred to as “the second brain”, containing cells that are similar to those within the brain. The microbiota within the gut play a key role in our overall brain function, affecting hormones, neurotransmitters, cytokines and short chain fatty acids that act via immune, endocrine, vagal and other pathways. Research has shown that the intestinal microbiota produce compounds that cross into the blood brain barrier. These signalling molecules and pathways affect our physical, mental and emotional wellbeing. “Psychobiotics” are defined as microbiota-targeted interventions such as “beneficial bacteria (probiotics) or support for such bacteria (e.g., prebiotics) that influence bacteria-brain relationships” (1).
The concept of bidirectional communication between the gut and the brain is well accepted, and is referred to as the gut-brain-microbiota axis. Early-stage studies to investigate the relationship between the gut microbiota and the brain have included mode of action studies, animal studies, preclinical work, and clinical studies. Impacts of supplements and nutritional interventions on healthy subjects and investigational therapeutics on disease states have also been studied. Probiotics can support cognitive and mental health by beneficially modifying the microbial community within the gut and by producing metabolites and other compounds that affect signalling between the gut and the brain.
Studies of major depressive disorder have been correlated with reduced Lactobacillus and Bifidobacteria and symptom severity has been correlated to changes in Firmicutes, Actinobacteria, and Bacteriodes. Gut microbiota that contain more butyrate producers have been correlated with improved quality of life (1).
A study in healthy women providing probiotic yogurt for four weeks showed an improvement in emotional responses as measured by brain scans (2). A subsequent study by Mohammadi et al. (3) investigated the impacts of probiotic yogurt and probiotic capsules over 6 weeks and found a significant improvement in depression-anxiety-stress scores in subjects taking the specific strains of probiotics contained in the yogurt or capsules. Other studies with probiotics have indicated improvements in depression scores, anxiety, postpartum depression and mood rating in an elderly population (4-7).
Other studies have indicated a benefit of probiotic supplementation in alleviating symptoms of stress. In particular, researchers have looked at stress in students as they prepared for exams, while also evaluating other health indicators such as flu and cold symptoms (1). In healthy people, there is an indication that probiotic supplementation may help to maintain memory function under conditions of acute stress.
A 2022 study by Meyer et al. (8) noted a connection between cognition and the presence of Akkermansia, Barnsiella, Lactinospiracaeae and Verrucomicrobia within the digestive tract. This study also indicated that butyrate plays a role. Butyrate is a metabolite of several beneficial bacteria. Animal studies have shown that butyrate protects against cognitive impairment, vascular dementia and metabolic risk factors that contribute to cognitive decline and dementia. As noted above, butyrate production has also been linked to improvements in major depressive disorder symptoms (1).
A review was conducted by Eastwood et al. (9) to assess the impact of probiotic use on cognition. The review found a positive effect of probiotics on cognition in 21 of 25 studies when the specific probiotic strain was administered as a therapeutic adjunct to people with conditions leading to impaired cognitive function.
Species of specific probiotic strains that are most commonly connected with cognition, mental health and stress include Lactobacillus, Bifidobacterium, Lactococcus and Streptococcus. Prebiotics and postbiotics may also stimulate specific probiotics and beneficial bacteria that affect communications between the gut and the brain, and ultimately mental and emotional health.
Consumers are actively seeking probiotic products for their potential health benefits. Consumer interest in probiotics related to stress, mental health, emotional health and cognition has increased 3 to 4-fold over the last twenty years based on Google Trends reports. Interest in probiotics for cognition is even higher in sectors of the population where cognitive function is paramount, such as first-responders, health care professionals, students, and anyone that relies on learning, memory and accuracy of information retention and transfer.
Probiotics and the microbiota play a significant role in cognition, mental and emotional health and wellbeing. Future perspectives into probiotics and gut-brain research includes building on present research, understanding mechanisms of action and an investigation of applications into neurodegenerative and neuromuscular conditions, including Parkinson’s and Alzheimer’s disease. There will be fascinating opportunities to further our understanding of the connection between probiotics and the gut microbiome, the brain and physical and mental health.
REFERENCES AND NOTES
- Cryan, J.F. et al. Physiol. Review. 99:1877-2013, 2019.
- Tillisch, K. et al. Gastroent. 144(7):1394-1401, 2013.
- Mohammadi, A.A. et al., Nutr. Neurosci. Nov. 19 (9): 387-395, 2016.
- Chong, H.X. et al. Benef. Microbes. 10 (4):355-373, 2019.
- Kato-Kataoka, A. et al. Benef. Microbes 7 (2):153-156, 2015.
- Langkamp-Henken, B. et al. Brit. J. Nutr. 113(3): 426-434, 2015.
- Takada, M. et al. Neurogastro. & Motility. 28 (7):1027-1036, 2016.
- Meyer K., et al. JAMA Network Open. 2022; 5(2):e2143941.
- Eastwood, J. et al. Neuroscience & Biobehav. Reviews,128: 311-327, Sept. 2021.
ABOUT THE AUTHOR
George Paraskevakos, MBA, is executive director of the International Probiotics Association (IPA) whose mission it is to promote the safe and efficacious use of probiotics throughout the world while being “The Global Voice of Probiotics ®”. Involved in the probiotics industry since 2007, Paraskevakos has grown the association from 40 to 110 companies worldwide; hosted numerous international probiotics conferences; published extensive probiotic papers and articles; and collaborated with fellow probiotics associations to further knowledge on probiotics effectiveness and safety. George represents the International Probiotics Association in the media, all probiotic stakeholders including government agencies and at the Codex Alimentarius and also serves on the advisory council for the Southwest College of Naturopathic Medicine & Health Sciences.
About IPA: The International Probiotics Association (IPA) is a global non-profit organization bringing together through its membership the probiotic sector’s stakeholders including but not limited to academia, scientists, health care professionals, consumers, industry and regulators. The IPA’s mission is to promote the safe and efficacious use of probiotics throughout the world. Holding NGO status before Codex Alimentarius, the IPA is also recognized as the unified Global Voice of Probiotics® around the world. To learn more about IPA, visit https://internationalprobiotics.org/