Gut microbiota profiles may correlate with cognitive performance in middle-aged and older adults, according to study results published in Clinical Nutrition.

Healthy middle-aged and older adults (N=169) were enrolled in this randomized, placebo-controlled, double-blind study at Kent State University in the United States. Participants were randomly assigned to receive Lactobacillus (L) rhamnosus GG (LGG) supplementation (n=86) or placebo (n=83). The LGG supplement consisted of 2 capsules containing 10 billion colony forming units of L rhamnosus GG and 100 mg prebiotic chicory root extract insulin. Cognitive performance was evaluated using the National Institute of Health (NIH) Toolbox for the Assessment of Neurological and Behavioral Function-Cognition and a battery of interactive tests. Gut microbiota was assessed in stool samples collected at baseline, after approximately 12 weeks of treatment, and at the follow-up.

The LGG and placebo groups included individuals with a mean age of 64.4±5.5 and 64.2±5.4 years; the male:female ratios were 38:48 and 28:55; BMI was 27.8±6.7 and 28.1±6.8 kg/m2; and they had 15.2±2.6 and 15.3±2.4 years of education, respectively.

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A total of 21 from the LGG and 23 from the placebo group were found to have cognitive impairment.

Overall, gut microbiota was dominated by Bacteroidetes (48%) and Firmicutes (46%).

Stratified by impaired and nonimpaired cognitive status, at baseline individuals with cognitive impairment had a greater abundance of Prevotella (P =.0136), specifically ANCOM-BC (P =.0004) and ALDEx2 (P =.0017).

Among the subset of individuals with the highest abundance of Prevotella among both cognitively impaired and intact groups, cognitive impairment associated with a lower evenness at the genus level (P =.0372) and significant clusters at the family (P =.03) and genus (P =.049) level compared with the cognitively intact group.

In a random set of 88 samples from 44 individuals, the individuals who received LGG supplementation had 11.5 times more Lactobacillus (P <.0001) compared with those who received placebo. The probiotic had an effect on paired beta diversity (P =.018), indicating a change in relative abundance but not in taxa overall.

The LGG supplementation had an effect among the subset of individuals with cognitive impairment, in which Dehalobacterium (P =2.07×10-9) and non-zero relative abundance of Prevotella genus subjects (P =2.33×10-5) were decreased compared with cognitively intact LGG recipients.

The study was limited by not evaluating metabolic activities, inflammation, and dietary patterns, which may have had significant interactions with the findings.

“Our results indicate that LGG had a marginal impact on overall microbiota composition and points to a specific response based on the host cognitive status,” the study authors noted. “Contrarily to most studies, which reported on the microbiome composition of MCI patients compared to other forms of cognitive dysfunction like AD, we compared MCI to healthy individuals aiming to provide information that could help in the early detection of cognitive aging. Finally, our analysis identified Prevotella ruminicola and Bacteroides thetaiotaomicron as taxa that could be modulated with pre, pro, or synbiotics to prevent or slow the progression of cognitive impairment.”

Disclosure: One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of the author’s disclosures.


Aljumaah MR, Bhatia U, Roach J, Gunstad J, Andrea M, Peril A. The gut microbiome, mild cognitive impairment, and probiotics: a randomized clinical trial in middle-aged and older adultsNutrients. 2019;11(2):305. doi:10.3390/nu11020305

This article originally appeared on Gastroenterology Advisor