Probiotics are supplements or fermented foods that contain potentially beneficial microorganisms, namely certain strains of bacteria, and some types of fungi. The microorganisms that make up the gut microbiome produce a variety of bioactive substances which influence the physiology of the host, particularly metabolism and the immune system. Disruptions to the microbiome are common in chronic disease. Probiotics are designed to modulate the microbiome toward a more healthful state. Probiotics show modest benefits in regulating some cognitive, immune, and metabolic parameters in clinical trials. Probiotics are safe for most people, but no optimal probiotic formulation has yet been identified for any condition.
Clinical trials show evidence for a protective effect of some probiotics for cognitive function in the context of stress and mild impairment, but variability in the probiotic formulation across studies prevents the identification of a specific probiotic with consistent cognitive benefit.
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Probiotic use is not associated with overall improved cognitive function in cognitively healthy people. Several clinical trials indicate that probiotics have the potential to mitigate some of the negative aspects of stress, with respect to cognitive function, sleep, and mood [1; 2; 3]. The cognitive effects are most apparent for emotional memory and decision-making tasks, and are accompanied by changes in brain activity patterns [2; 4]. The effects are likely mediated by the bioactive substances produced by the probiotic strains which have been shown to alter the activity of signaling chemicals in areas of the brain associated with emotional processing [5]. Since the functional effects of probiotic strains are highly dependent on an individual’s baseline microbiome and physiology, the efficacy of a given probiotic formulation can vary widely across individuals.
Clinical trials have shown modest benefits for probiotics in patients with mild cognitive impairment and early Alzheimer’s disease (AD) in improving cognitive scores on measures of memory and attention [6; 7]. The effects on cognition were accompanied by beneficial effects on immune system regulation and metabolism, such as blood lipid levels [7; 8]. A clinical trial in patients with severe AD found that probiotics had no effect on cognition or immune parameters in this population [9].
Probiotics have been safely used in the form of fermented foods for hundreds of years, and their use is not associated with increased risk for adverse events in clinical trials when tested in a wide variety of populations [10]. Due to the lower regulatory standards for supplements, foods may be a safer, more reliable option. The most common side effects are mild, temporary, and related to the gastrointestinal system, as the gut is the primary site of action for probiotics [11]. Probiotics can increase the risk for infection in severely immunocompromised patients under rare conditions when these microorganisms get into the bloodstream. Probiotics may interact with antibiotics and antifungal drugs [12].
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Probiotics are available as supplements and in the form of fermented foods, such as yogurt. The formulation, identity and quantity of the strains, and dosage vary widely across products [13]. No optimal probiotic preparation has yet been identified for any condition. In general, probiotics that contain strains of Lactobacillus or Bifidobacterium, at dosages of at least five to ten billion colony forming units, for at least 12 weeks were more likely to be associated with benefits in clinical trials [6]. Due to variability in the microbiome across individuals, different people will likely preferentially benefit from different probiotics.
More information on use and safety of probiotics at Drugs.com.
Full scientific report (PDF) on Cognitive Vitality Reports