A Practitioner's Guide to Probiotics: Neurological Conditions

Probiotic supplements contain beneficial microorganisms, similar to those found in the human gastrointestinal tract (79). When ingested, these live microorganisms confer a number of health benefits to the host (22). Particular strains of probiotics can provide neuroactive properties that may induce effects on the human brain, mind, and behavior. These kinds of probiotics are often referred to as psychobiotics (52).

Imbalances in the intestinal microbiota are believed to be involved in the development of certain neurological disorders and may modulate other affective and behavioral responses from the central nervous system (CNS). The signalling that takes place between the GI system and the CNS, the neuroendocrine system, the neuroimmune system, the sympathetic and parasympathetic autonomic nervous systems, and the enteric nervous system is commonly referred to as the gut-brain axis (9, 68). 

Probiotic supplements may support a healthy composition of bacteria in the gastrointestinal tract and improve cognitive and behavioral function by a number of mechanisms, including:

  • Modulation of neurotransmitters, such as norepinephrine, serotonin, acetylcholine, and corticotropin releasing factor, involved in the gut-brain axis
  • Metabolite conversion in regulation of the immune and nervous systems
  • Modulation of microbial metabolites and inflammatory cytokines that stimulate the vagus nerve
  • Downregulation of proinflammatory cytokines through anti-inflammatory modulation
  • Modulation of the HPA axis, hormones, and receptors (eg. GABA, opioid-μ, cannabinoid)
  • Prevention of dendritic atrophy, promotion of synaptic connections, and neurogenesis
  • Production of short-chain fatty acids (SCFAs) that can cross the blood-brain barrier and induce neuroprotective, cognitive, and antidepressant effects (9)

While probiotics are now commonly prescribed therapeutically and clinical research examining the relationship between the gut microbiome and neurological disorders is becoming increasingly available (55), clear guidelines for clinical application have yet to be established. This is particularly important as the effectiveness of probiotic supplementation may be dependent on the condition, strain, dosing, and duration of therapy (79). 

This guide provides an overview of the available research for the clinical application of probiotics in neurological conditions, including dosing and administration for single-strain and multi-strain probiotics.

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Safety Considerations & Contraindications

While probiotics are considered safe, rare short term side effects, such as gas and bloating, may occur (15). Isolated cases of bacteremia or fungemia have been associated with probiotics, though population data also indicates that there is no widespread risk of these complications (66). 

There is some limited evidence that probiotics should not be administered in critically ill patients, as demonstrated by an increased risk of mesenteric ischemia and mortality in a trial of patients with predicted severe acute pancreatitis (8).

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