Study finds age-dependent cognitive benefits from probiotic consumption

A new meta-analysis suggests that the consumption of probiotics may offer cognitive benefits, particularly for middle-aged and older adults. The research indicates that supplementing with these live bacteria can improve memory, processing speed, and spatial reasoning in aging populations. These findings regarding the relationship between gut health and brain function were published in the European Journal of Clinical Nutrition.

Cognitive abilities encompass the mental processes required for learning, problem-solving, and daily functioning. As individuals age, it is common to experience a gradual decline in these faculties. This can manifest as increased difficulty with memory, lower attention spans, or reduced executive function.

When this decline exceeds normal age-related patterns, it may signal the onset of neurodegenerative conditions. Current projections estimate that the number of people living with dementia could reach 152 million by the year 2050. This looming public health challenge has prompted researchers to identify accessible strategies to support brain health throughout the lifespan.

One area of intense scientific focus is the connection between the gastrointestinal tract and the brain. This biological pathway is often referred to as the gut-brain axis. It proposes that the trillions of microorganisms living in the human digestive system can influence neurological activity.

Previous studies have shown that the composition of gut bacteria often changes in people with neurological disorders. For instance, specific alterations in the microbiome have been observed in patients with Parkinson’s disease. Animal studies have further suggested that modifying gut bacteria can encourage the growth of new neurons.

Probiotics are supplements containing live beneficial bacteria intended to restore or enhance this internal ecosystem. Past reviews have attempted to summarize the effects of these supplements on the brain. However, those reviews typically focused on specific subgroups, such as people with Alzheimer’s disease or mild cognitive impairment.

Less was known about how these effects might differ across the entire human life cycle. HanQing Guo and a team of researchers from Ningxia Medical University in China aimed to address this gap. They sought to determine if the impact of probiotics on brain function varies depending on the age of the individual.

To investigate this, the research team conducted a meta-analysis. This statistical approach involves pooling data from multiple independent studies to identify broader trends and stronger evidence. The investigators searched major medical databases for randomized controlled trials published up to December 2023.

They established strict criteria for which studies to include. Eligible trials had to involve human participants who received at least one strain of live probiotic bacteria. There also had to be a control group for comparison.

The researchers excluded animal studies and observational reports. They also removed studies involving patients with gastrointestinal disorders to isolate the cognitive effects. Ultimately, the team selected 21 randomized controlled trials for their final quantitative analysis.

These 21 studies included a diverse range of participants. The subjects ranged from premature infants to adults over the age of 90. The trials utilized various standardized neuropsychological tests to measure mental performance.

The researchers categorized the data into specific cognitive domains. These domains included global cognition, executive function, processing speed, memory, attention, spatial ability, and verbal language skills. This categorization allowed for a nuanced view of exactly which mental skills were affected.

The analysis revealed that the effects of probiotics are indeed age-dependent. The most significant and broad benefits were observed in the middle-aged and elderly population. In this group, probiotic supplementation was associated with a statistically significant improvement in overall cognitive function.

Specific improvements were noted in delayed memory, which is the ability to recall information after a period of time. Older adults taking probiotics also showed faster processing speeds. This refers to the time it takes to perceive information and formulate a response.

Spatial ability also improved in the older demographic. This cognitive skill involves understanding the relationship between objects in physical space. The researchers found that the most effective interventions for this age group typically lasted about 12 weeks.

The effective dosage in these successful trials was often around 20 billion colony-forming units per day. This suggests that a sustained and sufficient intake is necessary to observe benefits in aging brains. The findings support the potential of probiotics as a supportive therapy for age-related cognitive decline.

The results were different for infants and children. The analysis showed no significant improvement in overall cognitive development for the youngest participants. However, there was a specific positive effect on executive function.

Executive function includes high-level skills such as planning, focusing attention, and managing multiple tasks. The researchers noted that these benefits in children appeared to require longer intervention periods. Trials showing positive results in children often involved supplementation lasting six months to three years.

For young adults, defined as those between 18 and 60 years old, the benefits were also narrow in scope. Probiotics did not lead to improvements in global cognition or memory for this group. The only significant change observed was an improvement in verbal ability.

This suggests that a healthy, fully developed brain in its prime may be less sensitive to the cognitive-enhancing effects of probiotics than an aging brain. The ceiling for improvement is likely lower in healthy young adults.

Across all age groups, the study found one consistent non-finding. Probiotic supplementation did not lead to significant improvements in attention span. This suggests that the biological pathways influenced by gut bacteria may not heavily impact the neural networks responsible for sustained attention.

The researchers proposed several biological mechanisms to explain the positive results. One primary theory involves the reduction of inflammation. Chronic inflammation is a known factor in neuronal damage and cognitive decline.

Probiotics may help modulate the immune system and reduce the production of inflammatory markers. This creates a healthier environment for brain cells to function. Another mechanism involves the direct production of neurotransmitters.

Certain strains of gut bacteria can produce chemicals like gamma-aminobutyric acid, dopamine, and serotonin. These chemical messengers are essential for mood regulation and signal transmission in the brain. By increasing the availability of these neurotransmitters, probiotics may support smoother neural communication.

The authors also highlighted the role of brain-derived neurotrophic factor. This is a protein that supports the survival of existing neurons and encourages the growth of new synapses. Some studies included in the analysis suggested that probiotics could increase serum levels of this vital protein.

Despite the positive findings, the authors acknowledge several limitations in their work. The number of high-quality trials available for analysis is still relatively small. Only 21 studies met the inclusion criteria, and some of those had small sample sizes.

There was also considerable variation in the types of probiotics used. The trials employed different strains of bacteria, such as Lactobacillus and Bifidobacterium, as well as different dosages. This heterogeneity makes it difficult to recommend a specific “brain health” formulation.

The definition of cognitive health also varied across the studies. Some participants were healthy, while others had mild cognitive impairment or Alzheimer’s disease. This mixture complicates the ability to apply the findings to the general population universally.

Some of the included studies had potential biases. For example, a few trials did not fully blind the participants or personnel to who was receiving the placebo. This could potentially influence the reported outcomes.

The researchers emphasize that probiotics should not be viewed as a cure-all. They are likely most effective when used as part of a broader strategy for health. This strategy should include a balanced diet and regular physical activity.

Future research is needed to validate these findings over longer periods. Longitudinal studies could help determine if the cognitive benefits persist after supplementation stops. Researchers also need to investigate how individual differences in genetics and existing gut flora influence the response to probiotics.

Personalized approaches may be the future of this field. It is possible that different individuals require different bacterial strains to achieve optimal cognitive support. Until then, this study provides promising evidence that caring for the gut may be a viable way to care for the aging brain.

The study, “Effects of probiotics on cognitive function across the human lifespan: a meta-analysis,” was authored by HanQing Guo, YanHua Liang, XueMei Qin, Qing Luo, XiuMei Gong, and Qinghan Gao.