Probiotics as a strategy to reduce the risk of cognitive decline. A topic that is finding a growing interest in the scientific community, to the point that a group of scientists from the University of Reading, England, decided to carry out a systematic review of the literature on the subject to give an account of what is now known about the neurocognitive effects of an intervention on the gut microbiota. The results of their analysis were recently published in Neuroscience & Biobehavioral Reviews.
Thirty papers were selected, all conducted in humans, with at least one live probiotic strain and with the evaluation of at least one indicator of cognitive abilities among memory, attention/concentration capacity and executive function, the latter understood as the ability to plan and implement projects aimed at achieving a goal. The results were grouped by age group.
Pediatric age
Three studies have examined children born prematurely, with very low birth weight, who were administered the probiotic until hospital discharge. Followed for variable periods, from 18 months to 5 years, the supplementation did not show any impact on cognitive development. Strains used in the different trials: L. reuteri, L. acidophilus and B. infantis, S. thermophilus and B. lactis. Same results in two studies on term infants, with L. rhamnosus/B. animalis and B.longum/L.rhamonos.
Adults
Four studies evaluated the effect of probiotic supplementation on hepatic encephalopathy, a complication of cirrhosis that can cause impaired memory and cognitive function.
In one case, participants with encephalopathy received probiotics for two months, showing a significant improvement already after 30 days of the various indicators examined, as, on the other hand, occurred in the control group. Finally, two studies of the remaining three, conducted on patients with cirrhosis but without overt hepatic encephalopathy, showed benefits on cognitive performance after 8-12 weeks of treatment.
Interesting results of a pilot study followed by a larger non-randomized placebo-controlled trial on HIV-positive patients treated with a multi-strain probiotic (L. plantarum, S. thermophilus, B. breve, L. paracasei, L. delbrueckii subsp. bulgaricus, L. acidophilus, B. longum and B. infantis) for six months. In both cases, there was significant improvement in mnemonic and verbal fluency tests.
Finally, three studies included people with fibromyalgia, chronic fatigue syndrome and depression. In the first case, an eight-week treatment with a multiseed consisting of L. rhamnosus GG, L. casei, L. acidophilus, and B. bifidus was shown to improve impulsivity-based behaviors. In the second, a four-week course of probiotics (L. rhamnosus, B. lactis, B. breve, and B. longum) plus antibiotic (erythromycin) resulted in better performance on memory, attention, speed of thought processing, and verbal fluency. In the third, eight weeks of treatment with probiotic (L. plantarum) and antidepressant demonstrated improvements in short-term memory and visual search in subjects with major depression compared with controls treated with the drug alone.
In healthy adult subjects, however, the studies reviewed showed no benefit with probiotic use.
Seniors
Three research studies have evaluated the effects of probiotic supplementation in older adults with mild cognitive impairment. In one pilot, single-arm study, 24 weeks of treatment with probiotics (B. breve) improved Mini-mental state examination (Mmse) scores. Subsequently, however, the same study, enlarged and with a placebo control group, showed no differences at 12 weeks in the two arms.
Three other studies on Alzheimer’s patients treated with probiotics for 12 weeks gave mixed results. Two (the first with L. acidophilus, L. casei, Lactobacillus fermentum and Bifidobacterium bifidum, the other with L. acidophilus, B. bifidum and B. longum), showed an improvement in Mmse scores, while the third, which used a different assessment test, found no significant effects.
Finally, two trials, controlled vs placebo, of 12 weeks in healthy elderly: one, with L. helveticus, showed a significant improvement in some cognitive functions, the other, with B. longum, B. infantis and B. breve, did not.
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