Dysbiosis

The gut microbiota refers to the community of microorganisms – mostly bacteria – that live within our gastrointestinal tract, primarily in the large intestine. These microorganisms include bacteria, viruses, and fungi, essential in digestion, metabolism, and immune function.

The gut microbiota is incredibly diverse, with hundreds of different species of microorganisms living in our gut. Each person’s gut microbiome is unique, influenced by diet, genetics, environment, and lifestyle.

The gut microbiota strongly impacts the overall maintenance of our health[1] – with the breakdown and absorption of nutrients from food, protection against harmful pathogens, production of vitamins and other beneficial compounds (e.g., short-chain fatty acids), and even mood influence.

“Gut microbiome” and “gut microbiota” are often used interchangeably, but they refer to slightly different things. The gut microbiota refers to the microorganism living within our gastrointestinal tract. On the other hand, the gut microbiome refers to the collective genomes of all the microorganisms that make up the gut microbiota. This includes not only the genetic material of the microorganisms themselves but also the genes and metabolic pathways they express.

Imbalances in the gut microbiome – known as dysbiosis – can lead to a range of health problems.

Dysbiosis can occur when there has been a shift in the quantity or variety of microorganisms (e.g., following infection or dietary changes) or when the balance between beneficial and harmful microorganisms is disrupted.

Dysbiosis has been linked to pathological conditions, such as obesity, type 2 diabetes, ulcerative colitis, neurodegenerative diseases, cardiovascular diseases, cancer, autoimmune diseases, allergies, depression, and anxiety[2]. This led to an explosion of interest in microbiota alterations in ageing, resulting in dysbiosis becoming recognized as a potential contributor to the ageing process.

To help prevent dysbiosis, supporting a healthy and diverse gut microbiome is essential. This can be done by eating a balanced diet rich in fibre, prebiotics, and probiotics, reducing stress, and avoiding unnecessary antibiotics and other medications.

The diversity of bacteria in the gut is established during childhood and tends to remain stable during adulthood. However, as we age, the composition and diversity of the gut microbiota naturally change, with a decline in beneficial bacteria, an increase in potentially harmful ones, and a decline in overall ecological diversity.

This can lead to chronic inflammation – a hallmark of many age-related diseases, including cardiovascular disease, diabetes, and Alzheimer’s disease. In older adults, dysbiosis has been associated with a decline in immune function and an increased risk of infections and chronic diseases.

Researchers have identified a microbiome pattern that is indicative of healthy ageing. A depletion of core taxa characterizes this pattern- specifically Bacteroides (a type of bacteria.)

“Core taxa” refers to the microorganisms commonly in most healthy individuals’ gut microbiome.

Furthermore, among individuals who approach extreme age, those with retention of high levels of Bacteroides and a less distinct gut microbiome are more likely to have a reduced chance of survival[3].

Gut microbiota become increasingly more unique to each individual with age[4].

According to the ELDERMET study, there is an increased prevalence of the core genera Bacteroides, Alistipes, and Parabacteroides in older individuals compared to younger controls. The study also found that changes in the gut microbiome composition with age were associated with frailty, cognition, depression, and inflammation[5].

The probiotic Lactobacillus plantarum (strain GKM3) promotes longevity
and alleviates age-related cognitive impairment in mice[6].

Gut microbiota-induced inflammaging and the consequent increase in insulin resistance can also be reversed by restoring the abundance of beneficial bacteria, such as A. muciniphila, in aged mice[7].

In a study of volunteers who were overweight or obese (and insulin-resistant), it was found that oral administration of pasteurized A. muciniphila improved insulin sensitivity, reduced insulin levels, and lowered total cholesterol levels in the blood[8].

Diets that restrict calorie intake, also known as calorie-restricted diets, can cause changes in the gut microbiota that lead to an increase in beneficial bacteria such as Lactobacillus and other species that may contribute to healthy ageing [9].

Researchers have been able to manipulate the health span and lifespan in mice via fecal microbiota transplantation. Transfer of the gut microbiota from old mice to young triggered chronic systemic inflammation[10]. Transferring in the other direction, from young to old, improved the cognitive function, fertility, and immune effectiveness of the old mice[11].

Collectively, these results underscore the causal links between ageing and dysbiosis and suggest that interventions aimed at protecting or restoring a more youthful microbiome may extend health span and lifespan.