Exploring the Influence of Gut–Brain Axis Modulation on Cognitive Health: A Comprehensive Review of Prebiotics, Probiotics, and Symbiotics

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Exploring the Influence of Gut–Brain Axis Modulation on Cognitive Health: A Comprehensive Review of Prebiotics, Probiotics, and Symbiotics

^1,3,4,5,

Zoltán Csizmadia

⁶ and

János Tamás Varga

^7,*

¹

Department of Public Health, Faculty of Medicine, Semmelweis University, 1089 Budapest, Hungary

²

National Institute for Haematology and Infectious Diseases, Department of Haematology and Stem Cell Transplantation, South Pest Central Hospital, 1097 Budapest, Hungary

³

Department of Neurosurgery, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA

⁴

Department of Health Promotion Sciences, College of Public Health, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA

⁵

Peggy and Charles Stephenson Oklahoma Cancer Center, Oklahoma City, OK 73104, USA

⁶

Faculty of Health Sciences, University of Pécs, 7621 Pécs, Hungary

⁷

Department of Pulmonology, Semmelweis University, 1083 Budapest, Hungary

^*

Author to whom correspondence should be addressed.

Nutrients 2024, 16(6), 789; https://doi.org/10.3390/nu16060789

Submission received: 8 February 2024 / Revised: 6 March 2024 / Accepted: 8 March 2024 / Published: 10 March 2024

(This article belongs to the Section Nutrition and Public Health)

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Abstract

Recent research exploring the relationship between the gut and the brain suggests that the condition of the gut microbiota can influence cognitive health. A well-balanced gut microbiota may help reduce inflammation, which is linked to neurodegenerative conditions. Prebiotics, probiotics, and symbiotics are nutritional supplements and functional food components associated with gastrointestinal well-being. The bidirectional communication of the gut–brain axis is essential for maintaining homeostasis, with pre-, pro-, and symbiotics potentially affecting various cognitive functions such as attention, perception, and memory. Numerous studies have consistently shown that incorporating pre-, pro-, and symbiotics into a healthy diet can lead to improvements in cognitive functions and mood. Maintaining a healthy gut microbiota can support optimal cognitive function, which is crucial for disease prevention in our fast-paced, Westernized society. Our results indicate cognitive benefits in healthy older individuals with probiotic supplementation but not in healthy older individuals who have good and adequate levels of physical activity. Additionally, it appears that there are cognitive benefits in patients with mild cognitive impairment and Alzheimer’s disease, while mixed results seem to arise in younger and healthier individuals. However, it is important to acknowledge that individual responses may vary, and the use of these dietary supplements should be tailored to each individual’s unique health circumstances and needs.

Keywords:

cognitive function; prebiotic; probiotic; symbiotic; dementia; randomized controlled trial

1. Introduction

The dietary habits and lifestyle of the Western civilized world have a significant impact on the gut microbiota, influencing cognitive functions [1,2,3]. Diets rich in added sugars and refined carbohydrates, with low fiber content and limited probiotic intake, can adversely affect the gut microbiota, potentially correlating with cognitive issues [1,4]. The prevalence of artificial additives, the consumption of pre-packaged, ultra-processed foods, and high-saturated fat diets can negatively influence both the gut microbiota and cognitive health and may be linked to cardiovascular problems as well [2]. The excessive use of antibiotics and other medications can harm beneficial gut bacteria, leading to long-term negative effects on cognitive functions [3]. Sedentary lifestyles, low levels of physical activity, and chronic stress can also detrimentally impact cognitive performance [5]. Therefore, maintaining and supporting a healthy gut microbiota can contribute to optimizing cognitive functions and play a crucial role in maintaining the balance between the brain and the gut.

As the aging of society poses significant challenges to healthcare systems and societies, it becomes increasingly important to recognize the interplay between gut health and cognitive well-being, especially in older populations. Estimates suggest that by 2030, one in six members of the global population will be aged 60 or older [6]. Furthermore, the number of individuals aged 60 and above is expected to double by 2050, potentially reaching 2.1 billion. Notably, the age group over 80 years old may triple between 2020 and 2050, reaching up to 426 million [6]. The World Health Organization (WHO) emphasizes several factors to preserve cognitive functions and support health in the elderly, including maintaining a balanced diet rich in vitamins, antioxidants, and nutrients; sustaining regular physical activity; avoiding smoking; limiting alcohol consumption; preventing social isolation; and maintaining social connections. All these factors are crucial for emotional and cognitive well-being [7].

The nourishment of the gut microbiota has long involved the use of probiotic products containing various beneficial strains, as well as fermented foods and strains that specifically stimulate proper brain function through gut–brain axis stimulation [8]. According to the WHO’s definition, probiotics are “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host” [9]. Probiotic dairy products contain beneficial bacteria (mainly lactobacilli and bifidobacteria) in sufficient quantities, which can potentially create a less hospitable environment for pathogens in the colon lumen, thereby hypothetically supporting the integrity of the gut flora and the immune system [10]. Another nutritional factor is dietary fibers acting as prebiotics (food for probiotic bacterial strains), as the diverse consumption of dietary fibers also promotes microbiome diversity [11]. They stimulate the growth and activity of beneficial bacteria, promote a healthy balance of the gut flora, and support digestion. Concurrently intaking probiotics and prebiotics (symbiotics) can promote a healthy gut flora balance and have strengthening effects on the immune and digestive systems [12]. Increasing research results confirm that supporting the gut flora with probiotics and strengthening the gut–brain axis can offer a new treatment alternative for those with mental health issues such as major depression, anxiety disorders, chronic fatigue syndrome, attention deficit hyperactivity disorder (ADHD), depression caused by irritable bowel syndrome (IBS), mood disorders, and stress-induced harm [13,14]. Moreover, even in healthy individuals exposed to increased stress, their positive effects on the brain and psychological well-being are evident, suggesting that their use is safe and necessary for everyone, especially in the context of Western nutrition and modern urban lifestyles [15,16]. Therefore, the aim of our comprehensive review is to examine the publications of the last 5 years, with a particular focus on the administration of probiotics, prebiotics, and symbiotics and the cognitive outcomes derived from their use.

 

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