The role of probiotics in mental health
Probiotics are microorganisms in the gastrointestinal tract, such as beneficial bacteria and yeasts, that have a positive health benefit for their host. The main probiotic genera are Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus. Prebiotics are complex carbohydrates, such as inulin and various oligosaccharides, that provide metabolic fuel for the probiotics. Products containing both prebiotics and probiotics are often referred to as synbiotics and can have powerful antioxidant properties due to their complementary and synergistic effects. The term psychobiotics has been introduced to designate probiotics that can influence central nervous system functions and brain networks involved in emotional and cognitive response.
Probiotics and prebiotics can help support mental health and may be clinically beneficial to those with depression, anxiety, attention deficit hyperactivity disorder (ADHD), Alzheimer’s, and autism spectrum disorder by promoting beneficial microbiota while helping to attenuate the proliferation of harmful ones. Probiotics can have a direct impact on the CNS by affecting brain-derived neurotrophic factor (BDNF), gamma-aminobutyric acid (GABA), dopamine, and serotonin. They have also been shown to decrease corticosteroid levels and mitigate the hypothalamic–pituitary–adrenal (HPA) stress response, thus regulating mood and emotions.
Alzheimer’s disease is the most common manifestation of progressive dementia and affects nearly 50 million people worldwide. It is believed to be caused by the formation of insoluble amyloid deposits in the brain. Changes in the microbiome and elevated biomarkers of inflammation and oxidative stress are reported to take part in the pathogenesis of neurodegenerative diseases of the CNS, including Alzheimer’s. Probiotics have the potential to decrease inflammation and increase acetylcholine levels in the CNS and have the potential to play a supportive role in alleviating the progression of neurodegenerative conditions.
Depression and anxiety are mental disorders of increasing concern. According to the World Health Organization, approximately 280 million people worldwide suffer from depression and more than 300 million people have an anxiety disorder. Microbiome dysbiosis can increase the release of lipopolysaccharides (LPS) which can activate a gastrointestinal inflammatory response. Pro-inflammatory cytokines can in turn impact the HPA axis inducing symptoms associated with anxiety and depression. Probiotics can produce metabolites from the fermentation of prebiotics that can affect brain processes and immune responses. These metabolites include certain fatty acids, tryptophan mediators, neurotransmitters, and neuropeptides, which are clinically relevant to those with anxiety and depression. A systematic review and meta-analysis of five randomized controlled trials (n = 458) observed that individuals receiving probiotic supplements displayed significant reductions in the incidence of depression.
Autism spectrum disorder is a complex neurodevelopmental condition with a wide range of symptoms expressed by challenges with social abilities and behavior, speech, and nonverbal communication. According to the Centers for Disease Control and Prevention, 1 in 36 children has been identified with ASD in the United States. Gastrointestinal dysfunction and permeability have been identified as the most prevalent physiological symptoms of ASD, suggesting a potential role for probiotics to influence the pathogenesis and severity of ASD. In a randomized controlled trial (n=37), children with ASD were randomly selected for treatment with six grams per day of a probiotic powder containing six strains of bacteria with one billion colony-forming units (CFUs) per gram. After four weeks, ASD-related symptoms and gastrointestinal symptoms decreased more in the treatment group compared to the control.
Which probiotic strains are associated with improved mental health?
There are several strains that have been shown to promote CNS function, balanced mood, normal stress responses, and support memory capabilities. These include L. acidophilus, L. rhamnosus, L. plantarum, L. casei, B. infantis, B. longum, and B. breve. Probiotic bacteria from the genera Lactobacillus and Bifidobacterium can have neuroprotective properties due to the production of neurotransmitters and neuropeptides, including GABA, serotonin, BDNF, and acetylcholine, which can influence brain physiology, emotional status, and mood. Multiple studies have demonstrated that Bifidobacterium and Lactobacillus strains can play a supportive role for individuals with anxiety, depression, obsessive-compulsive disorder (OCD), and autism spectrum disorder (ASD). A systematic review of fifteen clinical studies (n = 1,209) reported that subjects taking B. longum, B. breve, B. infantis, L. helveticus, and L. rhamnosus with doses between 108 and 1010 CFUs showed efficacy in improving psychiatric symptoms associated with anxiety, depression, ASD, OCD, and memory abilities.
Certain probiotic strains, alone or in combination with prebiotics, have shown positive implications for mental health:
Currently available research provides compelling evidence that there may be a role for probiotics in supporting mental health. Further research in the form of human randomized controlled trials may be warranted to elucidate the effect of probiotics on the pathogenesis and severity of mental health disorders and the corresponding mechanisms of action.
Learn more about probiotics:
Recent Meta-analysis Investigates Relationship Between Probiotics and Prediabetes
New Review Investigates the Efficacy of Different Probiotics in IBS
The Latest on Probiotics and Periodontal Health
Recent Randomized Controlled Trial Explores Efficacy of Probiotics on Chronic Urticaria
By Antonia Toupet, PhD
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