Today's research materials are a selection of recent studies on the gut microbiome and its relationship to the aging process. The scientific community has in recent years uncovered a great deal of new information regarding the way in which the gut microbiome both influences health and exhibits detrimental changes with age. Some of the microbes of the digestive tract are responsible for the generation of beneficial metabolites such as butyrate, indoles, and propionate. Unfortunately these populations decline in number with advancing age, and this negatively impacts tissue function throughout the body. Additionally, harmful inflammatory species increase in number. This contributes to the state of chronic inflammation that characterizes old age and accelerates the progression of all of the common age-related conditions.
The causes of age-related shifts in these microbial populations are not well understood, particular recently discovered changes that take place in earlier life. There is evidence for dietary changes to be involved, as well as the decline of the immune system's ability to suppress harmful microbes, and the loss of integrity of intestinal barrier tissue. Which of these are more significant or less significant is an open question, however. It is also an open question as to how great an influence this has on long-term health and longevity; it wouldn't be surprising to find it in the same ballpark as that of exercise.
This is an age-related change that is amenable to reversal in the near term. Animal studies show that fecal microbiota transplant from young animals to old animals resets the gut microbiome to a more youthful distribution of species, and results in improved health and extended life spans. This procedure is already carried out in human medicine for certain conditions, and could thus be expanded to other uses. Other potential approaches also exist, such as inoculation with bacterial proteins to encourage the immune systems to suppress harmful species, or sizable sustained dosage with a suitable mix of probiotics. We'll likely see many such initiatives in the years ahead.
The gastrointestinal tract is colonized by a set of microorganisms that include not only bacteria but also viruses, fungi, and protozoa. Unlike other microorganisms, these are not identified as pathogens by our immune system, but rather coexist symbiotically with the enterocytes. So far, it is known that its composition contains a total of 52 different phyla and up to 35,000 different bacterial species, the large majority being Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria.
As we age, progressive changes are produced in the morphology and function of the microbiota - a decrease in Firmicutes and Bifidobacterium, with diversity in the patterns of abundance for Clostridium. The mechanism by which the microbiota changes with age is not yet fully understood. Lifestyle changes, and particularly diet, play an important role. As aging is often accompanied by a reduction in quantity and variety of aliments containing fiber, it often leads to a risk of malnourishment. This could alter its diversity and provoke inflammatory and metabolic disruption, causing inflammatory diseases in the intestine, such as irritable bowel, obesity, etc. Additionally, the microbiota can modulate changes in aging related to innate immunity, sarcopenia, and cognitive function, which are essential components of the frailty syndrome.
Gut microbiota can crucially influence behavior and neurodevelopment. Dogs show unique similarities to humans in their physiology and may naturally develop dementia-like cognitive decline. We assessed 29 pet dogs' cognitive performance in a memory test and analyzed the bacterial 16S rRNA gene from fecal samples collected right after the behavioral tests. The major phyla identified in the dog microbiomes were Bacteroidetes, Firmicutes, and Fusobacteria, each represented by more than 20% of the total bacterial community. Fewer Fusobacteria were found in older dogs and better memory performance was associated with a lower proportion of Actinobacteria. Our preliminary findings support the existence of links between gut microbiota, age, and cognitive performance in pet dogs.
The study included 422,417 unrelated individuals in the UK Biobank who had undergone genotyping to identify their genetic make-up. Information was also collected on a wide range of diseases and other characteristics including BMI and blood pressure. The average age of participants was 57 years and 54% were women. The researchers found that higher levels of eleven bacteria (estimated from genetic data) were associated with a total of 28 health and disease outcomes. These included chronic obstructive pulmonary disease (COPD), atopy (a genetic tendency to develop allergic diseases like asthma and eczema), frequency of alcohol intake, high blood pressure, high blood lipids, and BMI. To take one example, higher levels of the genus Ruminococcus were linked with increased risk of high blood pressure.