- Alzheimer’s disease, which affects more than 6 million individuals in the United States, is the most common type of dementia.
- Probiotic supplementation may improve cognitive performance in patients with mild cognitive impairment, according to the findings of a meta-analysis.
- The analysis includes more evidence on the links between gut and brain health.
Probiotics and prebiotics may help to reduce the progression of several neurodegenerative illnesses, according to some research.
However, there are limited data on their effects in humans with Alzheimer’s disease or mild cognitive impairment (MCI).
Scientists from China’s Jiangnan University collaborated to examine the evidence so far. The results of their systematic review and meta-analysis have been published in the journal Foods.
“Our findings imply that probiotic intervention at early stages of Alzheimer’s disease, such as MCI, could improve cognitive performance and prevent disease development,” the authors conclude.
Probiotics, prebiotics, and synbiotics
ISAPP (International Scientific Association for Probiotics and Prebiotics) is a non-profit organization founded in 2002. It aims to advance probiotic, prebiotic, and synbiotic scientific research.
Probiotics are living bacteria that “provide a health benefit to the host when provided in suitable concentrations,” according to the ISAPP.
Prebiotics are a class of nutrients, sometimes known as substrates, that promote the growth of gut bacteria. Synbiotics are probiotics and prebiotics together.
Identifying relevant studies
The researchers searched numerous databases for studies involving Alzheimer’s or MCI individuals that were published between 1984 and early 2021.
After sifting through 294 research, Zhu and colleagues chose only eight for the systematic review and seven for the meta-analysis.
The major outcome of all of the investigations was cognitive function, which was assessed using the Mini-Mental State Examination (MMSE). Nutritional status, inflammatory biomarkers, metabolic profiles, and oxidative stress were all secondary outcomes.
Probiotic probiotics improved cognitive performance in people with MCI, according to the review’s authors. Participants with Alzheimer’s disease, on the other hand, saw less impressive gains. Overall, the writers come to the following conclusion:
“Compared with placebo or control interventions, probiotic supplementation considerably improved cognitive function in the participants with MCI, but it only caused a modest cognitive improvement in those with Alzheimer’s disease.”
The amount of probiotic strains given, their dosage, and the time of treatment all played a factor in how much cognitive improvement was achieved.
In persons with Alzheimer’s disease, probiotic treatment changed the structure and composition of their feces microbiota.
The co-authors mention research that suggest a decrease in fecal microbial diversity in Alzheimer’s patients. Only one study in the evaluation found that probiotic administration changed the structure and makeup of the fecal microbiota in Alzheimer’s patients.
A significant contribution to the research
Dr. David A. Merrill, Ph.D., is the director of the Pacific Neuroscience Institute’s Pacific Brain Health Center at Providence Saint John’s Health Center in Santa Monica, CA. He is an adult and geriatric psychiatrist. He was not a part of the evaluation process.
Dr. Merrill explained in an interview with Medical News Today:
“This meta-analysis — a study of studies — provides an important update about recent evidence showing that gut health may help brain function in older adults, especially those with mild cognitive impairment […] This is an important update on a topic which shows that our gut health impacts not only our systemic health but our emotional and cognitive well-being, as well.”
The review’s discovery that prebiotics may boost the production of brain-derived neurotrophic factor (BDNF) piqued Dr. Merrill’s interest:
“We know that BDNF levels drop in Alzheimer’s patients’ brains, and that this loss of BDNF is considered to contribute to the increased death of neurons in the brain. As a result, prebiotics may indirectly promote circulating levels of BDNF in the body, resulting in increased cell survival in the brain.”
The study’s limitations
The meta-analysis conducted by Zhu and colleagues had significant flaws, according to the researchers. To begin with, some of the studies had small sample sizes.
Furthermore, the studies studied did not take into account how other dietary supplements or lifestyles might have influenced the gut flora and metabolic profiles.
Different rating measures for cognitive impairment were also employed to measure cognitive function in the research included in the study. Only four of the research included in the review employed the widely used NINCDS-ADRDA dementia criteria.
In four of the investigations, no negative effects of probiotic supplementation were found. While probiotics have generally been found to be safe, older persons are more likely to experience major gastrointestinal, cutaneous, and systemic side effects.
Zhu and his colleagues are particularly concerned that errors in study design and commercial sponsorship may have skewed some outcomes.
Recommendations for future research
The authors of the paper expect that future studies will look into the negative effects of probiotic supplementation. Clinical trials that group and analyze persons with Alzheimer’s disease and MCI according to disease severity are also desired.
“Knowing the best effective dose of specific probiotic strains for varied illness states like memory loss remains a challenge,” Dr. Merrill added.
This meta-analysis does not indicate that probiotics will assist everyone with MCI, according to the psychiatrist. He did, however, say:
“If you’ve had a health stress to your gut, such as surgery or antibiotics, you might want to consider taking probiotics for a while to boost the diversity of beneficial bacteria in your gut and get it back to its best form.”